ALDEHYDES, KETONES AND CARBOXYLIC ACIDS
Chapter Outline
10.1 Nomenclature and Structure of Carbonyl Group
10.2 Preparation of Aldehydes and Ketones
10.3 Physical Properties
10.4 Chemical Reactions
10.5 Benzaldehyde
10.6 Nomenclature and Structure of Carboxylic Group
10.7 Preparation of Carboxylic Acids
10.8 Properties of Carboxylic Acids
Carbon compounds containing carbon-oxygen double bond, C = O is called carbonyl group. This is a very important financial group in organic chemistry.
10.1 NOMENCLATURE AND STRUCTURE OF CARBONYL GROUP
Aldehydes and ketones, both have the general formula, CnH2nO, and the common feature of both is carbonyl ( C = O ) group. Therefore, they are called carbonyl compounds. Aldehydes and ketones are the first oxidation products of primary and secondary alcohols, respectively. Aldehyde group is chain terminating group whereas ketonic group is not.
In aldehydes, –CHO group may be attached to a hydrogen atom or alkyl group or aryl group.
Example: HCHO, CH3CHO, CHO
In ketones, ( C = O ) group may be attached to two alkyl groups, two aryl groups, or one alkyl and one aryl group. If both the groups are same, they are simple ketones, and if they are different, they are mixed ketones.
Simple ketones (or) symmetrical ketones:
R–CO–R
Example:
CH3–CO–CH3, C2H5–CO–C2H5, etc.
Mixed ketones or unsymmetrical ketones: R–CO–R'
Example:
CH3–CO–C2H5, CH3–CO–C3H7, etc.
Aromatic ketones : Ar–CO–R
Example: COCH3 , CO etc.
Aldehydes and ketones are widespread in the animal and plant kingdoms. Their role in biochemical processes of life is very important. They are used in many food products and pharmaceuticals. Some of them are used as solvents and as adhesives, paints, resins, perfumes, plastics, fabrics, etc. Some of them are given below:
10.1.1 Nomenclature
There are two systems of naming carbonyl compounds.
Common System
Aldehydes and ketones are often called by their common names. Common names of the aldehydes are derived from the names of the corresponding carboxylic acids by replacing the suffix –ic acid with aldehyde.
The location of the substituent in the carbon chain is indicated by Greek letters α, β, γ, δ, etc. The α–carbon is the one directly linked to the aldehyde group, β–carbon to the next, and so on.
HCOOH (Formic acid) () O ← HCHO (Formaldehyde)
CH3COOH (Acetic acid) () O ← CH3CHO (Acetaldehyde)
CH3CH2COOH () O ← CH3CH2CHO (Propionic acid) (Propionaldehyde)
The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group and adding the word ‘ketone’. In case of simple ketones, they are named dialkyl ketones. However, mixed ketones are named by naming the two alkyl groups attached to the ketonic group as separate words in alphabetical order and adding the word ‘ketone’. The locations of substituents are indicated by Greek letters, α, α', β, β', and so on, beginning with the carbon atoms next to the carbonyl group, indicated as α, α'. Alkyl
phenyl ketones are usually named by adding the acyl group as prefix to phenone.
CH3–CO–CH3
Dimethyl ketone (Historical name is acetone)
CH3–CO–C2H5
Ethyl methyl ketone
α, β' –dichlorodiethyl ketone
COCH3
Methyl phenyl ketone (or) acetophenone
CO
Diphenyl ketone (or) benzophenone
IUPAC System
Th e IUPAC names of open chain aliphatic aldehydes and ketones are derived from the names of the corresponding alkanes by replacing the ending ‘–e’ with ‘–al’ and ‘–one’, respectively. In case of aldehydes, the longest carbon chain is numbered starting from the carbon of the aldehyde group, while in the case of ketones, the numbering begins from the end nearer to the carbonyl group. The substituents are prefixed in alphabetical order along with numerals indicating their positions in the carbon chain. When the aldehyde group is attached to a ring, the suffix carbaldehyde is added after the full name of the cyclic compound.
The name of the simplest aromatic aldehyde carrying the aldehyde group on a benzene ring is benzene carbaldehyde. However, the common name benzaldehyde is also accepted by IUPAC and so, other aromatic aldehydes are named substituted benzaldehydes.
When three or more aldehyde groups are attached to the unbranched carbon chain, then carbons in the – CHO are not included in the parent carbon chain and carbaldehyde suffix is used for –CHO. All aldehydeic groups are to be given identical treatment.
ketones, cyclic ethers, and unsaturated alcohols. They exhibit tautomerism with unsaturated alcohols. Aldehydes with four or more carbon atoms and ketones with five or more carbon atoms show chain isomerism. Ketones may exhibit metamerism.
CH2–CHO
CH–CHO
CH2–CHO 1 2 3
Propan-1, 2, 3 – 1 – Phenylpropan –tricarbaldehyde 1 – one (Propiophenone)
The common and IUPAC names of some aldehydes and ketones are given in Table 10.1.
10.1.2 Isomerism
Aldehydes show chain isomerism among the mselves and functional isomerism with
Chain Isomerism
Example:
Table 10.1 Common and IUPAC names of some aldehydes and ketones
1 HCHO
Methanal 2 CH3CHO
Ethanal 3 (CH3)2CHCHO
Methylpropanal 4 CH3 CH3–CH2–CH–CH2–CHO β–Methyl valeraldehyde 3–Methylpentanal
5 CH2 = CH – CHO Acrolein Propenal 6 CH3–CH=CH–CHO
Benzenecarbaldehyde 8 CHO Cyclohexane carbaldehyde Cyclohexanecarbaldehyde
9 CHO Br m–Bromobenzaldehyde 3–Bromobenzenecarbaldehyde 10 CHO CHO
Benzene–1, 2–dicarbaldehyde
cyclopentanone
ketone
none
10.1.3 Structure of Carbonyl Group
Both aldehydes and ketones have carbonyl group as the functional group. The carbonyl carbon is sp2 hybridised and, thus, it has three sp2 hybrid orbitals and one unhybridised p–orbital. It uses sp 2 hybrid orbitals to form three sigma bonds, one with oxygen atom and remaining two with two other atoms or groups (R or H). The bond angles are approximately 120°, as expected of a trigonal coplanar structure.
The unhybridised p–orbital of carbonyl carbon forms pi bond with oxygen atom by sideway
overlapping with half filled p–orbital of oxygen atom. In formaldehyde, HCH bond angle is slightly less than that of HCO bond angle, because double bond single bond repulsion is stronger than single bond single bond repulsion. The carbon–oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Consequently, oxygen attains a partial negative charge and carbon attains a partial positive charge, making the bond polar. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. The higher values of dipole moments of carbonyl compounds than the corresponding ethers and the high polarity of the carbonyl group is explained on the basis of resonance, involving a neutral and a dipolar structure.
TEST YOURSELF
1. The hybridisation of carbon in the carbonyl group is
(1) sp3 (2) sp2
(3) sp (4) sp3d
2. 2-pentanone and 3-pentanone are
(1) positional isomers
(2) functional isomers
(3) metamers
(4) ring chain isomers
3. Vinyl alcohol and ethanal are (1) metamers
(2) tautomers
(3) position isomers
(4) chain isomers
4. Which type of isomerism is shown by pentanone?
A) Chain
B) Position
C) Functional (1) A only (2) B only
(3) C only (4) A, B and C
5. The most polar compound among the given carbonyl compounds is (1) propanone (2) formaldehyde (3) propanal (4) hexan-3-one
6. IUPAC name of 3 CClCHO is (1) chloral (2) trichloro acetaldehyde (3) 1, 1, 1-trichloroethanal (4) 2, 2, 2-trichloroethanal
7. The number of structurally isomeric ketones with formula C6H12O is (1) six (2) two (3) five (4) four
8. In aldehydes, – CHO may be attached to (1) alkyl group only (2) H atom only (3) aryl group only (4) alkyl /aryl /H-atom
Answer Key
(1) 2 (2) 3 (3) 2 (4) 4 (5) 2 (6) 4 (7) 1 (8) 4
10.2 PREPARATION OF ALDEHYDES AND KETONES
Carbonyl compounds can be prepared from various compounds, like alcohols, nitriles, esters, hydrocarbons, etc.
10.2.1 Preparation from Alcohols
Oxidation: Aldehydes can be prepared by the regulated oxidation of primary alcohols. Oxidation may be carried out by acidified solution of potassium dichromate, or potassium permanganate, or manganese dioxide. The reaction is controlled by distilling out aldehyde as soon as it is formed, as aldehydes are very susceptible to further oxidation to carboxylic acids.
RCH2OH + (O) →RCHO + H2O
CH3CH2OH + (O)→CH3CHO + H2O
Pyridinium chloro chromate (PCC):
55 3 (CH)NHCrOCl +− , or Collin’s reagent, is a good oxidising agent for converting primary alcohols to aldehydes and secondary alcohols to ketones. Collin’s reagent is used in nonaqueous medium, dichloromethane.
Tertiary alcohol gives alkene through E 2 pathway.
33 3 OH | CHCCH | CH 0 AgorCu 300C → 32 3 CHCCH | CH −=
From Nitriles and Esters
Pyridinium dichromate (PDC), (C 5 H 5NH) 2Cr 2O 7, can also be used in place of PCC.
Jones reagent: CrO3 + H2SO4 + H2O in acetone is called Jones reagent. It can oxidise 1° alcohol to acid and 2° alcohol to ketones.
An alkyl cyanide is dissolved in ether and reduced with stannous chloride and hydrochloric acid. The iminochloride thus formed gets hydrolysed to give aldehyde.
22 SnCl HO HCl RCNRCHNH −≡→−=→ RCHO + NH4Cl
This reaction is called Stephen reaction. This method is for preparing only aldehydes. Alternatively, nitriles are selectively reduced by di-isobutylaluminium hydride, (DIBAL–H) to imines, followed by hydrolysis to aldehydes.
CH3CN 2 (i)DIBALH (ii)HO → CH3CHO
Catalytic Dehydrogenation
When vapours of a primary or a secondary alcohol are passed over copper or silver catalyst at 300°C, dehydrogenation takes place and an aldehyde or a ketone is formed, respectively.
o Cu(or)Ag 22 300C RCHOH RCHOH−→−+
() 0 CuorAg 32 32 300C CHCHOH CHCHOH→+
() 0 CuorAg 2 300C RCHOHR RCORH′′ −−→−−+ () o CuorAg 33 332 300C CHCHOHCH CHCOCHH→+
In the presence of these catalysts, if air is present, water is formed along with carbonyl compound. The dehydrogenation reaction is a better method of preparation because there is no risk of further oxidation of aldehyde or ketone.
CH3CH2OH () AgorCu air → CH3CHO + H2O
CH3CHOHCH3 () AgorCu air → CH 3COCH3 + H2O
CH3–CH=CH–CH2–CH2–CN 2 (i)DIBALH (ii)HO →
CH3–CH=CHCH2CH2CHO
Similarly, esters are also reduced to aldehydes with DIBAL-H.
CH3COOC2H5 2 (i)DIBALH (ii)HO → CH3CHO
CH3(CH2)9COOC2H5 →CH3(CH2)9CHO
DIBAL-H shows the temperature dependency. Esters are reduced to aldehydes at lower temperature, but at normal temperature, reduction gives alcohol.
Reductive Ozonolysis of Alkenes
Alkenes add on ozone to form unstable ozonide which, when decomposed by passing hydrogen in the presence of zinc dust and water, aldehyde or ketone or both are formed, depending upon the structure of alkene. R – CH = CH – R + O3 2 Zn,HO → 2RCHO + H2O
In place of zinc, we can also use CH 3–S–CH3 (DMS) and PPh3
|| CHSCH +H2O
(DMS)
3 HO22 → 3 O || PPh +H2O
From Alkynes
Addition of water to alkynes in the presence of sulphuric acid and mercuric sulphate gives aldehydes or ketones.
Acetaldehyde is obtained by passing acetylene gas through an aqueous solution of 40% sulphuric acid and 1% mercuric sulphate at 60°C. An unstable enol, vinyl alcohol, is formed as intermediate.
HC ≡ CH + H 2 O →[CH 2 =CH(OH)] CH3CHO
Acetone is obtained by passing propyne into an aqueous solution of 40% sulphuric acid and 1% mercuric sulphate at 60°C. An unstable enol, propenol–2, is formed as intermediate.
CH3–C ≡ CH+H2O→[CH3–C(OH)=CH2]→ CH3–CO–CH3
From Gem-Dihalides
Aldehydes are obtained by alkaline hydrolysis of terminal gem–dihalides
CH3CHCl2 2KOH 2KCl → CH3CH(OH)2 2 HO → CH 3CHO
Ketones are formed by hydrolysis of non terminal gem–dihalides.
–2KCl –H2O
This method is not used much since aldehydes are affected by alkali and dihalides are usually prepared from the carbonyl compounds.
From Grignard Reagent
Grignard reagents give aldehydes with hydrogen cyanide and ketones with alkyl cyanides.
R–C ≡ N + RMgX→R– C | R =NMgX
2 2HO → R– C | R =O + NH3 + Mg(OH)X
CH3–C ≡ N + CH3MgI 2 2HO →
CH3–3 C=O | CH + NH3 + Mg(OH)I
Alkyl cyanides react with Grignard reagent in ether solvent to form an addition compound, which on acid hydrolysis, gives a ketone.
CH3CH2 – C ≡ N + C6H5 MgBr ether → NMgBr
3 HO 32 CHCHC + −→
65CH O
32 CHCHC
65CH Propiophenone
10: Aldehydes, Ketones and Carboxylic Acids
From Acid Chlorides
Acid chlorides can be reduced into aldehydes with hydrogen over catalyst palladium supported on barium sulphate. This reaction is called Rosenmund reduction. Ketones cannot be prepared by this method.
RCOCl + H2 4 Pd BaSO → RCHO + HCl
CH3COCl + H2 4 Pd BaSO → CH3CHO + HCl
Treatment of acyl chlorides with dialkyl cadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones.
2R MgX + CdCl2→R2Cd + 2Mg(X)Cl
2R'–CO–Cl + R2Cd→2R'–CO–R+CdCl2
2CH3COCl+(CH3)2Cd→ 2CH3COCH3 + CdCl2
R 2 Cd only react wi th acid halide due to less polarity of R–Cd bo nd and more
el ectrophilicity of carbonyl carbon in acid halide O || (RCCl).
From Carboxylic Acids
By heating a mixture of the calcium salts of formic acid and any one of its homologues, aldehyde is formed.
over manganous oxide as catalyst at 300°C, aldehyde is formed.
RCO2H + HCO2H MnO → RCHO + CO2 + H2O
R2CO is obtained as byproduct. The reaction proceeds via the manganous salt.
By heating the calcium salt of any monocarboxyllic acid other than formic acid, ketone is formed.
2R C H
+ 2CaCO3
By passing a mixture of the vapours of formic acid and any one of its homologues
If mixture of calcium salts is used, mixed ketones are obtained.
(R1CO2)2 Ca + (R2CO2)2 Ca →2R1COR2+2CaCO3
By passing the vapour of any monocarboxylic acid other than formic acid over managanous oxide at 300°C, ketone is formed. MnO 2 222 2RCOHRCOCOHO →++
Q. How is acetone obtained from isopropyl bromide?
Sol. Step - I: Isopropyl bromide is converted into isopropyl alcohol, by hydrolylis with aq. KOH.
Step - II: Isopropyl alcohol is converted into acetone by dehydrogenation, using copper.
KOH
Try yourself: () XY aq.KOH Cu,300C 25 CHCHBrCH25 ° →→
In this reaction, identify the organic compounds X and Y formed, giving their systematic names.
Ans: X is penta–3–ol and Y is pent–3–one
TEST YOURSELF
1. X 32 3 CHCHOHCHCHO → , here X is / are
(A) Cu/573K (B) Ag/573 K (C) PCC
(D) CrO3+H2SO4 (E) C6H5N2+Cl
(1) D only (2) A, D and E only (3) B and E only (4) A and E only
2. The most suitable reagent for the conversion of 2 RCHOHRCHO → is (1) K2Cr2O7 (2) CrO3 (3) KMO4 (4) PCC
3. In which of the following processes is acetone one of the final products?
(1) Ozonolysis of ethyne (2) Oxidation of 2-butene with KMnO4/H+
(3) Oxidation of 2, 3 -dimethyl -2-butene with KMnO4/H+;∆
(4) Dehydrogenation of 1-propanol
4. 2, 3 - dimethyl - 2 - butene, on reductive ozonolysis, gives (1) acetone
(2) acetaldehyde (3) butanone (4) formaldehyde
5. X 32 32 CHCHCNCHCHCHO. −≡→
The reagent X is (1) SnCl2/HCl/H2O, (2) H2/Pd−BaSO4 (3) LiAIH4/ether (4) NaBH4 /ether/H3O+
6. Which of the following, on heating with aqueous KOH, produces acetaldehyde?
(1) CH3COCl (2) CH3CH2Cl (3) CH2ClCH2Cl (4) CH3CHCl2
7. Rosenmund’s reduction is used for the preparation of (1) carboxylic acid (2) aldehydes (3) esters (4) carbohydrates
8. The first oxidation product of which of the following alcohols is a ketone with the same number of carbon atoms?
(1) CH3CH2CH2OH
(2) (CH3)2CHCH2OH
(3) CH3CH(OH)CH3
(4) (CH3)3C - OH
9. 2 3 1)SnClHCl 2HO RCN RCHO + + −→−
This reaction is known as (1) Rosenmund (2) Williamson (3) Stephen (4) Kolbe
10. Ketones cannot be prepared in one step from (1) Alcohols (2) Alkenes (3) Alkynes (4) Esters
Answer Key (1) 1 (2) 4 (3) 3 (4) 1 (5) 1 (6) 4 (7) 2 (8) 3 (9) 3 (10) 4
10.3 PHYSICAL PROPERTIES
At ordinary temperature, formaldehyde is a gas, while next ten members of the aldehyde series are colourless volatile liquids. Ketones up to eleven carbon atoms are also colourless volatile liquids. The higher members of both the series are solids.
The lower members of aldehydes and ketones, such as formaldehyde, acetaldehyde, and acetone are miscible with water in all proportions, because they form hydrogen bond with water.
The solubility of these compounds in water decreases with the increase in the size of the alkyl group. It is due to the hydrophobic nature of the alkyl group. All aldehydes and ketones are fairly soluble in organic solvents, like benzene, ether, chloroform, etc.
Lower aldehydes have unpleasant sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent and more fragrant. Many naturally occurring carbonyl compounds are used in the blending of perfumes and flavouring agents. Acetone is a highly inflammable liquid.
Aldehydes and ketones have relatively high boiling points, as compared to hydrocarbons or ethers of comparable molecular masses. It is due to appreciable intermolecular (dipole–dipole) attraction, as the aldehydes and ketones are polar molecules. These dipole–dipole interactions are, however, weaker than intermolecular hydrogen bonding in alcohols. Consequently, boiling points of aldehydes and ketones are relatively lower than those alcohols of comparable molecular masses. The following compounds have almost same molecular mass (58–60). Their boiling points order is: 1–propanol (alcohol, 370 K) > propanone (ketone, 329 K) > propanal (aldehyde, 322 K) > methoxy-ethane (ether, 281 K) > butane (alkane, 273 K).
TEST YOURSELF
1. Highest boiling point is observed for (1) methoxy ethane
(2) acetone
(3) propanal
(4) propan-1-ol
2. False statement among the following is (1) formaldehyde is soluble in water
(2) acetic acid exists as dimer in benzene
(3) acetone is a pleasant smelling liquid
(4) acetaldehyde is insoluble in water
3. Which of the following gives a crystalline compound with (1) HCN (2) NaHSO3
(3) RMgX (4) ROH
4. Identify the correct order of boiling points of the following compounds.
A) CH3CH2CH2CH2OH
B CH3CH2CH2CHO
C) CH3CH2CH2COOH
(1) A > B > C
(2) C > A > B
(3) A > C > B
(4) C > B > A
5. Choose the correct statements among the following.
A) Methanal is a gas at room temperature.
B) Ethanal is a volatile liquid.
C) Methanal, ethanol, and propanone are soluble in water.
D) Higher aldehydes are pungent smelling.
(1) All
(2) A, B, C only
(3) B, C, D only
(4) A, B, D only
Answer Key
(1) 4 (2) 4 (3) 2 (4) 2
(5) 2
10.4 CHEMICAL REACTIONS
Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons.
Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one substituent.
The reactivity of the carbonyl group towards the addition reactions depends upon the magnitude of the positive charge on the carbonyl carbon atom. Any substituent that increases the positive charge on the carbonyl carbon must increase its reactivity towards addition reactions. The introduction of electron withdrawing group (–I effect) increases the reactivity, while introduction of alkyl group decreases the reactivity, as +I effect and steric hindrance increase.
Reactivity order of carbonyl compounds:
Nucleophilic Addition Reactions
The carbonyl group is a highly polar group as the p–electrons of the double bond are shifted to the more electronegative oxygen ato m.
Chloral is more reactive than acetaldehyde as chlorine atoms increase the positive charge on the carbonyl carbon.
Th us, the carbonyl group has two active centres which can be easily attacked. The positively charged carbon is readily attacked by electron rich nucleophiles. The negatively charged oxygen is attacked by electron deficient electrophiles. However, during addition reaction, nucleophilic attack occurs because the anion produced is more stable than the cation.
In the first step, planar sp2 hybridised carbon changes to sp 3 and a tetrahedral alkoxide intermediate is produced. This intermediate captures a proton from the reaction medium to give the electrically neutral product. If nucleophile is weak, the reaction requires an acid catalyst.
Mechanism of nucleophilic addition under acidic conditions:
10.4.1 Nucleophilic Addition Reactions
A ldehydes and ketones are highly reactive compounds. Since both possess the same carbonyl functional group, they undergo similar chemical reactions. The characteristic reactions of aldehydes and ketones are nucleophilic addition reactions.
I n acidic conditions, the first step plays an important role. Specially, protonating the carbonyl group generates a very powerful electrophile.
It is true that the carbonyl group is already a fairly strong electrophile. However, a protonated carbonyl group bears a full positive charge, rendering the carbon atom even more electrophilic. This is especially important when weak nucleophiles, such as H2O or ROH, are employed.
Hydrate Formation
When an aldehyde or ketone is treated with water, the carbonyl group can be converted into a hydrate.
Addition of Sodium Bisulphite
The position of equilibrium generally favours the carbonyl group rather than the hydrate, except in the case of very simple aldehydes, such as formaldehyde.
Crystalline solid derivatives are formed when aldehydes or ketones are shaken with saturated aqueous solution of sodium bisulphite. This reaction is used in the separation of aldehydes and ketones from non-carbonyl compounds. Being a reversible reaction, the addition compounds can be decomposed by dilute mineral acids or aqueous alkalis to regenerate the original aldehyde or ketone. This reaction can be used for separation and purification of aldehydes and methyl ketones.
Addition of Hydrogen Cyanide
Both aldehydes and ketones react with hydrogen cyanide (sodium cyanide and dilute sulphuric acid) to form cyanohydrins. The reaction occurs very slowly with pure hydrogen cyanide. It is catalysed by a base and the generated cyanide ion, being a strong nucleophile, readily adds on to carbonyl compounds. Cyanohydrins are useful synthetic intermediates.
The position of the equilibrium lies largely to the right hand side for most aldehydes and to the left for most ketones, due to steric reasons. The hydrogen sulphite addition compound is water soluble and can be converted back to the original carbonyl compound by treating it with dilute mineral acid or alkali. Therefore, these are useful for separation and purification of aldehydes.
Addition of Grignard Reagent
Aldehydes and ketones react with Grignard reagent to from an adduct, which on hydrolysis, yields the corresponding alcohols.
(Tertiary alcohol)
The reaction of Grignard reagent with methanal produces a primary alcohol, with other aldehydes, a secondary alcohol, and with ketone, a tertiary alcohol.
Addition of Alcohols
Aldehydes react with alcohols in the presence of dry HCl gas to form acetals. In this reaction, the addition of one molecule of alcohol to one molecule of aldehyde results in the formation of a hemiacetal. A hemiacetal contains both an ether as well as alcohol functional groups. It is an unstable compound and cannot be isolated. It further reacts with alcohol to form stable acetal. Acetals are dialkoxy compounds (geminal diethers) and have properties similar to ethers.
Hemiacetal
Acetal
Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals. Dry HCl protonates oxygen of C=O and increases the electrophilicity of the carbonyl carbon, facilitating the nucleophilic attack of ethylene glycol.
Ethylene glycol ketal
Acetals and ketals are hydrolysed with aqueous mineral acids to yield corresponding aldehydes and ketones, respectively. Ketones do not ordinarily react with monohydric alcohols.
Addition of Ammonia
Ammonia reacts with aldehydes (except formaldehyde) and ketones to form the products called imines. Acetaldehyde reacts with ammonia to form acetaldiamine ammonia and loses a molecule of water to form ethanalimine.
Ketones form complex ketonic amines. Acetone reacts with ammonia to form acetone ammonia which loses a molecule of water to form propanonimine. Alkanamines are unstable. Imines on hydrogenation in the presence of Ni catalyst give alkanamines.
10.4.2 Nucleophilic Addition Elimination Reactions
Carbonyl carbon, being electrophilic can be attacked by nucleophile, then the resultant substance may undergo elemination. This reaction is found with derivatives of ammonia.
Reaction with Ammonia Derivatives
Aldehydes and ketones react with a number of ammonia derivatives to form compounds containing carbon nitrogen double bonds with elimination of water molecule. These reactions are called condensation reactions.
Important derivatives of ammonia:
■ Hydroxyl derivative of ammonia is hydroxylamine.
■ Amino derivative of ammonia is hydrazine.
■ Phenyl derivative of hydrazine is phenyl hydrazine.
■ 2, 4-dinitrophenyl derivative of hydrazine is 2, 4–dinitrophenyl hydrazine.
■ Amido derivative of hydrazine is semicarbazide.
In general, if we represent these derivatives by H2N–G, then their reaction with aldehydes and ketones can be represented as follows:
The condensation products of aldehydes or ketones,
■ with hydroxylamine are called oximes,
■ with hydrazine are called hydrazones,
■ with phenyl hydrazine are called phenyl hydrazones,
■ with 2, 4–dinitrophenyl hydrazine are called 2, 4–dinitrophenyl hydrazones, and
■ with semicarbazide are called semicarbazones.
The various ammonia derivatives and their reaction products with carbonyl compounds are summarised in Table 10.2. For carrying out these reactions, the medium should be slightly acidic. The optimum pH of the medium is around 3.5. It should not be strongly acidic. Reactions of the above type are basically addition reactions but pro ceed with the elimination of simple molecules, like water. Hence, they are called condensation reactions.
Table 10.2 Ammonia derivatives and their products with carbonyl compounds
Group, G
Name of the reagent
–R Amine, NH2R C NR
Substituted imine (Schiff’s base)
–OH Hydroxylamine, NH2OH C NOH Oxime
–NH2 Hydrazine, NH2NH2 C NNH2 Hydrazone
–NHC6H5 Phenylhydrazine, NH2NHC6H5 C NNHC6H5 Phenylhydrazone NO –2 NH
NO2 2, 4–Dinitrophenylhydrazine (DNP/DNPH), NO N2 H2NH NO2 (Brady’s reagent/ Bosche’s reagent)
–NHCONH2 Semicarbazide, NH2NHCOHN2
Q. Out of two –NH2 groups of semicarbazide, only one is involved in the formation of semicarbazone. Explain.
Sol. The lone pair of electrons of –NH 2 group
attached to O || C is involved in conjugation with the p –electrons of C=O. As a result, the electron pair of the –NH2 group is not available for nucleophilic attack on carbonyl carbon whereas other terminal –NH2 group is free to attack the carbonyl carbon.
Try yourself:
How-many C–N sigma bonds are found in acetaldehyde–2, 4–dinitrophenyl hydrazone?
Ans: Four
C=NNHNO2 NO2 2, 4–Dinitro–phenylhydrazone
C NNHCONH2 Semicarbazone
10.4.3 Reduction
Reduction to alcohols: Aldehydes and ketones, on mild reduction, give primary and secondary alcohols, respectively. This type of reduction is carried out either catalytically with hydrogen in the presence of Ni, Pt, or Pd, or chemically with lithium aluminium hydride, or sodium borohydride, or sodium in ethanol.
Ni 22 RCHOHRCHOH +→
CH3CHO + H2 Ni → CH3CH2OH () Ni 2 RCORHRCHOHR +→
CH3COCH3 + H2 Ni → CH3CH(OH)CH3
Reduction to hydrocarbons: The carbonyl group can be reduced to methylene group, resulting in the formation of alkanes by any one of the following reagents.
Clemmensen’s reduction: Carbonyl compounds are reduced to alkanes using zinc amalgam and concentrated hydrochloric acid.
R – CHO + 4(H)→ R – CH 3 + H2O
CH3CHO + 4(H) → CH3–CH3 + H2O
R – CO – R + 4(H) → R – CH2 – R + H2O
CH3COCH3 + 4(H) → CH3CH2CH3 + H2O
General features of the reaction:
■ Clemmensen reduction of acid-sensitive substrates and polyfunctional ketones is rarely successful in yielding the expected alkanes.
■ Selective reduction of aldehydes or keto groups is not possible by this method on compounds containing other functional groups, which can be reduced by metal and acids.
Wolff Kishner reduction: Carbonyl compounds are reduced to alkanes using hydrazine, followed by heating with sodium or potassium hydroxide in high boiling solvent, such as ethylene glycol.
R – CHO + NH2NH2→ R – CH3 + H2O + N2
CH3CHO + NH2NH2 KOH 180-200°C →
CH3 – CH3 + H2O + N2
R – CO – R + NH2NH2→ R – CH2 – R + H2O + N2
H3COCH3+NH2NH2 KOH boil →
CH3CH2CH3 + H2O + N2
General features of the reaction:
■ Esters, lactones, amides, and lactams are hydrolysed under the reaction conditions.
■ Sterically hindered carbonyl compounds are deoxygenated more slowly than unhindered ones, so higher reaction temperatures are required.
■ Can’t be used for a,b-unsaturated carbonyl compounds
Bimolecular reduction: Two molecules of ketones undergo reduction in the presence of Hg/Mg to form pinacol. Upon treatment with mineral acids, pinacol is converted into pinacolone.
This transformation involves dehydration and rearrangement is called pinacolpinacolone rearrangement. H3C 2 H3C Acetone H3C H3C O C C CH3 CH3 MgHg benzene heat CO=→
2, 3-Dimethylbutan -2,3-diol (pinacol)
Meerwein Ponndorf Verley (MVP)
reduction: Aldehydes and ketones can be reduced to corresponding alcohols by heating them with aluminium isopropoxide in excess of isopropyl alcohol. This reaction is highly specific. The other functional groups, such as carbon-carbon double bond or nitro group, remain unaffected. The co-product, acetone, is continuously distilled off to drive the equilibrium in favour of the alcohol product.
[(CH3)2CHO]3 Al H H OH OH
R CH3 R' + + CH3COCH3 O R R' C C C
10.4.4 Oxidation
Oxidation of aldehydes: Aldehydes are easily oxidised and thus act as strong reducing agents. They are oxidised to the corresponding
carboxylic acids containing the same number of carbon atoms. The oxidation of aldehydes does not involve the cleavage of carboncarbon bond. Since aldehyde group is chainterminating group, it is easily oxidised by even mild oxidising agents like Tollens’ reagent, Fehling’s solution, or Benedict’s solution, along with strong oxidising agents, like nitric acid, acidified potassium permanganate, or potassium dichromate.
Oxidation with Tollen’s Reagent
Tollen’s reagent is ammoniacal solution of silver nitrate. On warming with this reagent, aldehydes form a silver mirror on the walls of the container. The reaction is also known as silver mirror test for aldehydes.
RCHO + Ag2O→RCOOH + 2Ag ↓ (Black)
CH3CHO+2CuO→CH3COOH + Cu2O ↓ (Brick red)
Benedict’s solution is a mixture of solutions of copper sulphate, sodium citrate, and sodium carbonate. The reaction of aldehydes with Benedict’s solution is same as that with Fehling’s solution. Aldehydes reduce Benedict’s solution to give reddish brown precipitate. Aromatic aldehydes reduce Tollens’ reagent, but not Fehling’s solution or Benedict’s solution.
[RCHO + 2[Ag(NH3)2]+OH–→ 32
RCOOH2Ag4NHHO] +↓++
CH3CHO+ Ag2O →CH3COOH + 2Ag ↓ (Black)
CH3CHO + 2[Ag(NH3)2]OH→
CH3COONH4+2Ag ↓ (Black)+3NH3 +H2O
Oxidation with Fehling’s Solution
Fehling’s solution is an alkaline solution of cupric ion complexed with sodium potassium tartarate (Rochelle salt). Fehling’s solution A is freshly prepared alkaline copper sulphate and Fehling’s solution B is sodium potassium tartarate. These two solutions are mixed in equal amounts, called Fehling’s reagent. On heating an aldehyde (called Fehling’s solution) with Fehling’s reagent, a reddish brown precipitate is obtained. Aromatic aldehydes do not respond to this test.
RCHO + 2CuO→RCOOH + Cu 2O ↓ (Brick red)
RCHO + 2Cu2+ + 5OH–→
RCOO– + 3H2O + Cu2O ↓
Oxidation of ketones: Ketones are generally oxidised under vigorous conditions, with strong oxidising agents, like concentrated nitric acid, acidified potassium permangate, or acidified potassium dichromate. Oxidation of ketones involves cleavage of bond between carbonyl carbon and a–carbon on either side of keto group, giving a mixture of carboxylic acids having lesser number of carbon atoms. (Popoff’s rule).
CH3–CO–CH3 3 (O)
Conc.HNO →
HCOOH + CH 3COOH
[] 123 O
1222 RCHCCHR || O −−−−→
R1COOH + R2CH2COOH
(Breakage of C1 – C2 bond)
R1CH2COOH + R2COOH
(Breakage of C2 - C3 bond)
Since ketones are not oxidised by mild oxidising agents, they do not reduce Tollen’s reagent, Fehling’s solution, and Benedict’s solution. Hence, these reagents are used to distinguish between aldehydes and ketones.
Oxidation with sodium hypohalite:
Acetaldehyde and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less
10: Aldehydes, Ketones and Carboxylic Acids 18
than that of carbonyl compound. The methyl group is converted to haloform. This oxidation does not affect a carbon-carbon double bond, if present in the molecule.
Aldol Condensation
Aldehydes: Two molecules of an aldehyde having at least one a–hydrogen atom undergo condensation in the presence of dilute alkali, such as NaOH, Ba(OH) 2 or K 2CO 3, etc., to form b –hydroxy aldehydes (aldol). This is known as aldol reaction. The aldols lose water to give a,b–unsaturated carbonyl compounds, which are aldol condensation products, and the reaction is called aldol condensation.
Iodoform reaction with sodium hypoiodite is also used for the detection of CH3CO group or CH3CH(OH) group, which produces CH3CO group on oxidation.
Q. When a few millilitres of Tollen’s reagent is added to a test tube A and the contents are warmed, a silver mirror is formed. But when the same reagent is added to another test tube B, silver mirror is not formed in the same manner. Both the compounds in A and B have the same formula, C 3H6O. Solve it.
Sol. Tollen’s reagent is ammoniacal silver nitrate, [Ag(NH3)2] NO3. It is a mild oxidising agent (E° (Ag(NH3)2+ / Ag = + 0.15 V).
Hence, it can oxidise only aldehydes but not kentones.
So, the test tube A must be having the propionaldehyde (CH3CH2CHO) but test tube B must have acetone (CH3–CO–CH3).
Try yourself:
With Fehling’s Solution O xidation of the compound O CHO gives a salt, X. Wha t is the organic anion of the salt? Ans: 4–Oxocyclohexane carboxylate anion
10.4.5
Other Reactions
a –Hydrogen atoms of carbonyl compounds are acidic in nature due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base. The aldehydes and ketones undergo a number of reactions due to the acidic nature of a –hydrogen.
(Crotonaldehyde)
Ketones: In the presence of Ba(OH)2, acetone undergoes condensation and gives diacetone alcohol. A b-hydroxy ketone (ketol) is formed.
2CH2COCH3
(CH3)2C(OH)–CH2COCH3
Diacetone alcohol
(CH3)2C=CHCOCH3
Mesityl oxide
Carbonyl compounds that do not contain a–hydrogen atoms, like formaldehyde, benzaldehyde, etc., do not undergo this reaction.
Crossed Aldol Condensation
When aldol condensation is carried out between two different aldehydes or ketones, if both of them contain a –hydrogen atoms, a mixture of four different products is formed. Two of them are called cross aldols. The following reactions take place when acetaldehyde and propionaldehyde condense together.
2CH3CHO→CH3–CH=CH–CHO But-2-enal
2CH3CH2CHO→CH3–CH2–CH=C(CH3) CHO 2-Methylpent-2-enal
CH3CHO + CH3CH2CHO →
CH3 – CH = CH – CHO +
But-2-enal (Self aldol product)
CH3 – CH2 – CH = C(CH3) CHO
2-Methyl pent-2-enal (Self aldol product)
CH3–CH=C(CH3)CHO+CH3–CH2–CH=CH–CHO
2-Methylbut-2-enal Pent-2-enal (cross aldol) (cross aldol)
In cross aldol reaction, ketones can also be used as one component.
Cannizzaro Reaction
Aldehydes that do not have an a –hydrogen atom undergo self oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of aldehyde is reduced to alcohol while another is oxidised to acid salt. When formaldehyde is treated with concentrated alkali, one molecule is reduced to methyl alcohol while another is reduced to formic acid salt.
HCHO + HCHO + KOH KOH → CH3OH + HCOOK
I sobutyraldehyde, although it possesses an alpha hydrogen, underegoes Cannizzaro reaction.
200ºC
32 2(CH)CHCHONaOH Isobutyraldehyde +→
322 (CH)CHCHOH Isobutylalcohol + 32 (CH)CHCOONa sodiumisobutyrate
Though Cl 3 C–CHO and (C 6 H 5 ) 3 C – CHO have no alpha hydrogen, they cannot undergo Cannizzaro reaction.
Other examples:
HCOO H H Δ OD
Crossed Cannizzaro Reaction
In crossed Cannizzaro reaction, the more reactive aldehyde undergoes oxidation and forms salt of carboxylate, whereas less reactive aldehyde undergoes reduction and forms alcohol.
CHO CH2OH Δ KOH HCOO– + +HCHO
Intramolecular Cannizzaro Reaction
CHO CH2OH CHO COONa Δ NaOH
Q. When benzaldehyde and acetaldehyde mixture is treated with dil. NaOH at normal temperature, immediately, cinnamaldehyde (C 6 H 5 –CH=CHO) is formed. How is it formed?
Sol. The reaction between benzaldehyde and acetaldehyde under the influence of dil. NaOH is crossed aldol condensation.
C6H5 – CHO + CH3 – CHO dil.NaOH → 65 2 OH | CHCHCHCHO
2 HO → 65 O || CHCHCHCH −=−−
The initial aldol product undergoes dehydration readily, as the final product, a,b –unsaturated carbonyl compound has conjugation of C = C of benzene ring with the carbonyl group | CO−=
Try yourself:
What is the common name of the product of crossed aldol condensation product formed, when benzaldehyde and acetophenone are involved?
Haloform Reaction
Ans: Benzalacetophenone,
Compounds containing methyl ketonic group (CH3CO–) undergo haloform reaction. Both acetaldehyde and acetone respond to haloform reaction when treated with halogen and alkali. Halogen can be chlorine, bromine, and iodine.
CH3CHO + 3X2 + 4NaOH →
HCOONa + CHX3 + 3H2O + 3NaX
CH3COCH3 + 3X2 + 4NaOH →
CH3COONa + CHX3 + 3H2O + 3NaX
CHI3 is a yellow precipitate.
10.4.6 Tests for Carbonyl Compounds
Carbonyl compounds give orange, red, and yellow coloured needle type crystals with 2, 4–dinitrophenyl hydrazine, called Bosche’s reagent or Brady’s reagent. Then, aldehydes and ketones are differentiated with other reagents.
■ Aldehydes give silver mirror (black precipitate) with Tollens’ reagent, but not ketones.
■ Aldehydes give red precipitate with Fehling’s solution, but not ketones.
■ Aldehydes give red precipitate with Benedict’s solution, but not ketones.
■ Aldehydes restore the pink colour of Schiff’s base, but not ketones.
Schiff’s reagent is p–rosaniline hydrochloride (pink/magenta dye) aqueous solution decolourised by sulphur dioxide.
10.4.7 Uses of Carbonyl Compounds
■ Acetaldehyde is used in the preparation of acetic acid, acetic anhydride, ethyl acetate, vinyl acetate, chloral, 1, 3– butadiene, polymers, dyes, and drugs.
■ Acetaldehyde is used as an antiseptic inhalent in nose troubles.
■ Acetone and ethylmethy ketones are used as solvents for cellulose acetate, cellulose nitrate, resins, etc.
■ Acetone is used for storing acetylene gas and its transportation.
■ Acetone is used in the preparation of chloroform, iodoform, sulphonal, and chloretone.
10.4.8 Uses of Formaldehyde
The 40% solution of formaldehyde (formalin) is used as disinfectant, germicide, and antiseptic. It is used for the preservation of biological specimens. It is used in making synthetic plastics, like bakelite, urea-formaldehyde resin, etc. Many carbonyl compounds are well known for their odour and flavours.
Carbonyl compounds, like vanillin (from vanilla beans), salicylaldehyde (from meadow sweet), and cinnamaldehyde (from cinnamon) have very pleasant fragrances. They are also used to manufacture solvents like acetone and for preparing materials like adhesives, resins, paints, perfumes, plastics, fibres, etc. Vanillin is 4-hydroxy-3-methoxybenzene carbaldehyde.
TEST YOURSELF
1. In Clemmensen reduction, carbonyl compounds are treated with (1) zinc amalgam +HCl (2) sodium amalgam +HCl (3) zinc amalgam + nitric acid (4) sodium amalgam +HNO3
2. The increasing order of the rate of HCN addition to compounds I to IV is I) HCHO II) CH3COCH3 III) PhCOCH3 IV) PhCOPh (1) III<IV<II<I (2) I<II<III<IV (3) IV<II<III<I (4) IV<III<II<I
3. A, CH3 H 1. CH3MgBr 2. H3O+ C O
Here, compound A will be (1) 1° alcohol (2) 2° alcohol (3) 3° alcohol (4) 4° alcohol
4. Carbonyl compounds readily undergo (1) nucleophilic substitutions (2) electrophilic addition reactions (3) nucleophilic addition reactions (4) elimination reactions
5. Acetone is treated with excess of ethanol in the presence of HCl gas. The product obtained is
(1) (CH3)2 C OH OC2H5
(2) (CH3)2 C OC2H5 OC2H5
(3) CH3CH2CH2 CH3 C O
(4) CH3CH2CH2 CH2CH2CH3 C O
6. Acetone adds up which of the following without the elimination of water molecule? (1) NH2−OH (2) 2, 4 – DNP (3) H2N−NH2 (4) HCN
7. Which of the following does not undergo aldol condensation?
(1) ClCH2CHO (2) CCl3−CHO (3) C6H5CH2HO (4) CH3CHO
8. 4 || NaBH 32 O CHCHCCHO → product(s)
Product in the above reaction is (1) CH3CH2CHOHCH2OH (2) CH3CH2COOH+CO2 (3) CH3CH2COCH2OH
(4) CH3CH2CH(OH)CHO
9. Which one of the following does not form addition product with NaHSO 3 solution?
(1) HCHO (2) C6H5COCH3 (3) C6H5CHO (4) CH3CHO
10. Which of the following can give a positive test with 2, 4-D.N.P and negative test with Tollen’s reagent, and can also react with NaOI to give a yellow precipitate?
(1) CH3-CHO (2) CH3−CH2−CO−CH2−CH3 (3) CH3−CH2−CO−CH3 (4) 33 CHCHCH | OH
Answer Key (1) 1 (2) 4 (3) 2 (3) 3 (5) 2 (6) 4 (7) 2 (8) 1 (9) 2 (10) 3
10.5 BENZALDEHYDE
Benzaldehyde is the simplest aromatic aldehyde which occurs in bitter almonds and it is also known as oil of bitter almonds.
10.5.1 Preparation
Chromyl chloride oxidises toluene to a chromium complex, which on hydrolysis, gives benzaldehyde. This reaction is called Etard reaction.
CrO 2 Cl 2 CH(OCrOHCl2)2 + CS2
3
Chromic oxide in acetic anhydride oxidises toluene or substituted toluene to benzylidene diacetate, which on hydrolysis with aqueous acid, gives benzaldehyde. CrO 3 + CH 3 + (CH3CO)2O 1-10oC CH(OCOCH3)2
Benzoyl chloride, on reduction with hydrogen in the presence of Lindlar’s catalyst (Rosenmund reduction), gives benzaldehyde.
10.5.2 Properties of Benzaldehyde
Benzaldehyde undergoes addition reactions with hydrogen cyanide, sodium bisulphite, Grignard reagent, etc., just like acetaldehyde. Benzaldehyde undergoes condensation reactions with hydroxylamine, hydrazine, phenyl hydrazine, semicarbazide, etc., forming the corresponding condensation products.
Cannizzaro Reaction
Benzaldehyde undergoes self-oxidation reduction (disproportionation) reaction on treatment with concentrated alkali due to lack of hydrogen, forming benzyl alcohol and sodium benzoate.
Side chain chlorination of toluene gives benzal chloride. Followed by hydrolysis, it gives benzaldehyde. This is a commercial method.
CH3 CHO CHCl2
Cl2, hν H2O , 100°C
When benzene is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde. This reaction is called Gattermann−Koch reaction.
CH3 CHO CHCl2
Cl2, hν H2O , 100°C
Gattermann aldehyde synthesis: Benzene is teated with a mixture of HCN and HCl in the presence of anhydrous AlCl 3 to form benzaldiminium tetrachloroaluminate (III), which is hydrolysed to produce benzaldehyde. This is also called Gattermann formulation. + HCN + HCl AlCl3
CH=NH2AlCl4 H2O
Cross Aldol Condensation
Benzaldehyde undergoes cross condensation with a ketone in dilute alkali. CHO + COCH3–0 OH 20C →
CH=CH–CO
1,3-Diphenylprop-2-en-1-one
Aromatic aldehydes and ketones undergo electrophilic substitution in which the carbonyl group acts as a ring deactivating and meta –directing CHO324 0 HNO/HSO 010C → CHO NO2
Q. An organic compound (X) with molecular formula C 8 H 8 O forms an orange red precipitate with 2, 4-DNP reagent and responds to iodoform test. It neither
decolourises Baeyer’s reagent or bromine water and also it neither reduces Tollens’ reagent or Fehling’s reagent. Compound (X) gives a carboxylic acid (Y) with molecular formula C 7 H 6O 2 on drastic oxidation with chromic acid. Give the equations.
Sol.
Try yourself:
An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2, 4-DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens’ nor Fehlings’ reagent. What is the compound A?
Ans: ‘A’ is acetophenone
TEST YOURSELF
1. Select the incorrect one for the final product (P) in Etard’s reaction.
(1) P : Aromatic carbonyl compound
(2) P : Gives silver mirror with Tollen’s reagent
(3) P : Can participate in Cannizaro reaction
(4) P : Gives brick red ppt with Fehling’s solution
2. Example of electrophilic aromatic substitution reaction is (1) CO.HCl Anthyd AlCl3 CuCl
(2) CrO2Cl
+ (3)
3. 2 v HO 32 h PhCH2ClA? −+
(1) Ph-CHO (2) Ph-COOH
(3) Ph-CH2-OH (4) Ph-COCl
4. Oxidation of toluene to benzaldehyde can be easily carried out with which of the following reagents?
(1) CrO3/acetic acid, H3O+
(2) CrO3/acetic anhydride, H3O+
(3) KMnO4/HCl, H3O+
(4) CO/HCl, anhydrousAlCl3
5. The reagent used for the separation of acetaldehyde from acetophenone is (1) NH2OH
(2) NaHSO3
(3) NaOH/I2
(4) C6H5NHNH2
6. The product formed by the reaction of an aldehyde with a primary amine is (1) carboxylic acid
(2) aromatic acid
(3) Schiff’s base (4) ketone
7. The product formed in Gattermann−Koch benzal chloride reaction from benzene is (1) chlorobenzene
(2) benzol chlordie
(3) benzaldehyde
(4) acetophenone
8. An aldehyde which undergoes Cannizzaro’s reaction and reduces Schiff’s reagent but does not reduce Fehling’s solution is (1) CH3CHO
(2) HCHO
(3) C6H5CHO
(4) salicylaldehyde
9. Which of the following compounds does not react with NaHSO3?
(1) HCHO
(2) C6H5COCH3
(3) CH3COCH3
(4) CH3CHO
10. Toulene, when heated with alkaline KMnO4 followed by acidification, gives ‘A’. A, on decarboxylation, gives B. B, in the presence of CO + HCl / CuCl, gives C. The reaction B→C is
(1) Gattermann−Koch reaction
(2) Stephen’s reaction
(3) MPV reduction
(4) Etard reaction
11. Which of the following compounds gives a positive Tollen’s test but negative Fehling test?
(1) Acetaldehyde
(2) Benzaldehyde
(3) Acetophenone
(4) Acetone
Answer Key
(1) 4 (2) 1 (3) 1 (4) 2
(5) 2 (6) 3 (7) 3 (8) 3
(9) 2 (10) 1 (11) 2
10.6 NOMENCLATURE AND STRUCTURE OF CARBOXYLIC GROUP
Carbon compounds which possess a carboxyl functional group, COH || O are called
carboxylic acids. Higher members of aliphatic mono-carboxylic acids occur in fats as esters of glycerol. Hence, they are called fatty acids. The general formula of aliphatic carboxylic acids is C nH2nO2, represented by RCOOH.
The common names of acids are derived from the source of that particular acid. HCOOH is named formic acid as it is obtained from red ants (formica means red ant). CH3COOH is named acetic acid as it is present in vinegar (acetum means vinegar). CH3CH2CH2COOH is named butyric acid as it is present in rancid butter. CH3(CH2)3COOH, valeric acid, is present in the root of valerian plant.
In common system, the acids, except formic acid, are named derivatives of acetic acid.
Example: CH3CH2COOH is methyl acetic acid, (CH3)3C–COOH is trimethyl acetic acid, etc.
In IUPAC system, the secondary suffix –oic acid is included after an appropriate root word and primary suffix. Systematic name of a saturated carboxylic acid is alkanoic acid. The names are listed in Table 10.3 and Table 10.4
3 CHCHCHCHCOOH 54|3|21 CHCl
is called b –chloro– g –methyl valeric acid. Its IUPAC name is 3–chloro–4–methylpentanoic acid.
Table 10.3 Aliphatic carboxylic acids
HCOOH
CH3COOH
CH3CH2COOH
CH3CH2CH2COOH
(CH3)2CHCOOH
HOOC–COOH
HOOC–CH2–COOH
HOOC(CH2)2COOH
HOOC(CH2)3COOH
HOOC(CH2)4COOH
HOOC–CH2–CH(COOH)–CH2 COOH
Formic acid
Acetic acid
Propionic acid
Butyric acid
Isobutyric acid
Oxalic acid
Malonic acid
Succinic acid
Glutaric acid
Adipic acid
Methanoic acid
Ethanoic acid
Propanoic acid
Butanoic acid
2–Methylpropanoic acid
Ethandioic acid
Propandioic acid
Butandioic acid
Pentandioic acid
Hexandioic acid
Propane - 1, 2, 3 - tricarboxylic acid
Table 10.4 Aromatic carboxylic acids
acid
acid)
10.6.1 Isomerism
Carboxylic acids may exhibit chain isomerism. T hey do not have metamers. Esters are functional isomers of carboxylic acids.
CH3COOH is isomeric with methyl formate, HCOOCH3.
Functional isomers of C 2 H 5 COOH are CH3COOCH3 and HCOOC2H5
Q. What are the functional isomers of propanoic acid?
Sol. Functional isomers of carboxylic acids are esters, hydroxy aldehydes, hydroxy ketones and hydroxy oxiranes.
Propanoic acid can have the following functional isomers
■ Esters are HCOOC2H5, CH3COOCH3
■ Hydroxy aldehyde, CHO–CH 2CH2–OH
■ Hydroxy ketone, 32 O || CHCCHOH
■ Hydroxy oxiranes, 22 CHCHCHOH \O /
Try yourself:
How many functional isomers can acetic acid have?
Ans: Three
10.6.2 Acidic Nature
Carboxylic acids ionise in water and release H ⊕ forming a carboxylate ion which is its conjugate base. Proton is accepted by water in aqueous solutions of acid.
Applying law of mass action, the equilibrium constant is given as, K eq = 3 2
RCOOHO
As water is in large excess and its concentration does not change much, the equilibrium constant is written as,
K a = 3
RCOOHO RCOOH −+
K a is acid dissociation constant. As the value of K a increases, the strength of the acid also increases.
The negative value of logarithm of K a is denoted as pKa; pKa = –log Ka. As the value of pKa decreases, strength of acid increases. So strength of a carboxylic acid increases with increase in K a and decreases with increase in pKa.
Carboxylic acids are stronger in acidic character than alcohols and phenols. Unlike phenols, carboxylic acids react with weaker bases such as carbonates and bicarbonates to liberate carbon dioxide gas. This reaction is useful in detecting the presence of carboxyl group in an organic compound.
2RCOOH + 2Na→ 2RCOONa + H 2
RCOOH + NaOH → RCOONa + H 2O
2RCOOH+Na2CO3→2RCOONa +H2O+CO2
RCOOH+NaHCO3→RCOONa+H2O+CO2
It is a reversible reaction and equilibrium is established. The carboxylate anion, RCOO– is stabilised by resonance:
The pKa value of hydrochloric acid is – 7.0, benzoic acid is 4.19, acetic acid is 4.76, and that of trifluoroacetic acid (CF 3COOH) (the strongest organic acid) is 0.23. Strong acids have pKa values less than 1, moderately strong acids have between 1 and 5. The pKa values of weak acids lie in between 5 and 15 and extremely weak acids have greater than 15.
Though the conjugate base of phenol, phenoxide ion has resonance structures, they are non-equivalent and that too in which the negative charge is present on the less electronegative carbon atom. In the resonance structures of carboxylate ion, the negative charge is present on more electronegative oxygen and that too, the two resonance structures are equivalent. Hence, the resonance in carboxylate ion is more important than in phenoxide ion, so carboxylic acids are more acidic than phenols.
Effect of substituent on the strength of acids: The strength of an acid depends on the stability of its conjugate base RCOO –Greater the stability of the conjugate base, stronger is the acid. Stability of the conjugate base depends on spreading of charge. Greater the charge spreading, more is the stability and less is the strength of the conjugate base. Correspondingly, the parent acid becomes stronger acid.
Charge spreading can take place by resonance or inductive effect. Groups with –I or –M effects increase the strength of an acid and +I or +M effects decrease the acidic strength. Presence of electron withdrawing groups increases the strength of the acid and electron releasing groups decreases the strength of the acid by de-establishing the conjugate base.
The effect of the following groups in increasing acidity order is:
C6H5 < I < Br < Cl < F < CN < NO 2 < CF3
The K a values of important carboxylic acids are listed in Table 10.5.
Table 10.5 The K a values of important carboxylic acids
4.21 × 10–5
NCCH2COOH 3.65 × 10–3
FCH2COOH 2.57 × 10–3
ClCH2COOH 1.36 × 10–3
Cl2CHCOOH 5.33 × 10–2
Cl3CCOOH 2.32 × 10–1
HOOC–COOH 5.4 × 10–2
COOH
CH2 1.7 × 10–3
COOH
Based on the K a values, the following is the decreasing acidity order:
CF3COOH > CCl3 COOH > CHCl2COOH
> O 2 NCH 2 COOH > NCCH 2 COOH > FCH2COOH > ClCH2COOH > BrCH2COOH > HCOOH > ClCH2CH2COOH > C6H5COOH
> C 6 H 5 CH 2 COOH > CH 3 COOH > CH3CH2COOH
The –NO 2 group increases strength by exerting –M and –I effects and the –OCH 3 group decreases strength by exerting +M effect.
HCOOH > C6H5COOH > CH3COOH >
O2NCOOH > COOH >
H3COCOOH
When groups such as phenyl or vinyl are directly attached to the carboxylic acid, its acidic character is increased, contrary to expected decrease due to resonance as shown
This is due to greater electronegativity of sp 2 hybridised carbon to which carboxyl carbon is attached.
Acidic strength due to –I effect depends on positions : α−>β−>γ−
CH3CH2CHCl–COOH > CH3CHClCH2–COOH > ClCH2CH2CH2–COOH
Acidic strength due to –I effect also depends on the nature of the group.
NO2–CH2COOH > CN–CH2COOH > OH – CH2COOH
–M effect is more pronounced at para position as compared to that at meta position.
Try yourself:
Among the compounds, acetic acid, ethylalcohol, water, acetylene and ethane, how many can react with sodium metal?
Ans: Four
TEST YOURSELF
1. Propionic acid can also be named
(1) methyl methanoic acid
(2) methyl acetic acid
(3) methyl ethanoic acid
(4) ethyl acetic acid
2. Which of the following compounds does not have a carboxyl group?
(1) Methanoic acid (2) Ethanoic acid
(3) Picric acid (4) Benzoic acid
3. Which of the following is a pair of functional isomers?
(1) CH3COCH3, CH3CHO
(2) C2H5CO2H, CH3CO2CH3
(3) C2H5CO2H, CH3CO2C2H5
(4) CH3CO2H, CH3CHO
4. IUPAC name of phthalic acid is (1) benzene-1, 4-dicarboxylic acid
The ortho-substituted isomer of every substituted benzoic acid (whether the substituent is electron releasing or electron withdrawing) is relatively stronger than the corresponding para and meta isomer. This is called ortho effect.
Q. Among the compounds, phenol, acetylene, ethyl alcohol, formic acid, benzene sulphonic acid, and trinitrophenol, which compounds give effervescence upon addition with NaHCO3?
Sol Acids stronger than carbonic acid can react with NaHCO3 releasing CO2 gas, thus effervescence is observed. Such compounds among the given are formic acid, HCOOH, benzene sulphonic acid, C6H5–SO3H, trinitrophenol or picricacid.
(2) benzene-1, 2-dicarboxylic acid (3) benzene-1, 3-dicarboxylic acid
(4) 2-Phenylethanoic acid
5. Number of structural isomers (carboxylic acids and esters) with the formula C 2H4O2 is/are
(1) 1 (2) 2
(3) 3 (4) 4
6. Vinegar is (1) 6 – 10% acetic acid
(2) 50% acetic acid
(3) 6 – 10% oxalic acid (4) 75% valeric acid
Answer Key
(1) 2 (2) 3 (3) 2 (4) 2
(5) 2 (6) 1
10.7 PREPARATION OF CARBOXYLIC ACIDS
Carboxylic acids can be prepared from alcohols, esters, cyanides, etc., as follows.
10.7.1 From Primary Alcohols and Aldehydes
Carboxylic acids are prepared by the oxidation of primary alcohols or aldehydes, using acidic, alkaline or neutral potassium permanganate or potassium dichromate and chromium trioxide in acidic media.
RCH2OH 4227 24 KMnO(or)KCrO HSO → RCHO
4227 24 KMnO(or)KCrO HSO → RCOOH
CH3CH2OH 4227 24 KMnO(or)KCrO HSO → CH3CHO
4227 24 KMnO(or)KCrO HSO → CH3COOH
CH3(CH2)6CH2OH 3 24 CrO HSO → 1- Octanol
CH3(CH2)6COOH Octanoic acid
CH3(CH2)8COOH
3 24 CrO HSO → 1- Decanol CH3(CH2)8COOH Decanoic acid
Strong oxidising agent:
Hot KMnO4, Hot K2Cr2O7, Conc. KMnO4, Conc.K2Cr2O7, Acidified KMnO4, Acidified K2Cr2O7,
Oxidation of alcohol by strong oxidising agent:
CrO3/H+
no reaction
10.7.2 From Grignard
Reagents
Grignard reagents combine with carbon dioxide (dry ice) and form a salt. The salt gives a carboxylic acid on hydrolysis.
RMgX + CO2 Dry ether → R–COO–MgX
2 HO H + → RCOOH + Mg(OH)X
CH3MgBr + CO2→ CH3COOMgBr
3 HO + → CH3COOH + Mg(OH)Br
The acid formed has one carbon atom more than the alkyl group present in the Grignard reagent ascending the series.
10.7.3 From Cyanides, Esters, and Amides
Alkyl and aryl nitriles on acid or alkaline hydrolysis give amides, which on further hydrolysis, give carboxylic acids.
RC ≡ N 2 HO HorOH + → RCONH2 2 HO H(or)OH+− →
RCOOH+NH3
This method serves as a very good synthetic method for the preparation of carboxylic acids.
CH3CN 2 HorOH HO +− → CH3CONH2 +− ∆ → HorOH CH3COOH+NH3
Esters also give carboxylic acids on hydrolysis in the presence of dilute mineral acids.
RCOOR' + H2O RCOOH + R'OH
CH 3 COOC 2 H 5 2 HO,H + → ← CH 3 COOH+ C2H5OH
During base hydrolysis, carboxylates are formed, which on acidification, give corresponding caboxylic acids.
CH3CH2COOC2H5 NaOH → ←
no reaction
CH3CH2COONa 3 HO + → ← CH3CH2COOH
10: Aldehydes, Ketones and Carboxylic Acids
Acidic hydrolysis of esters gives directly carboxylic acids.
COOC2H5
3 HO + COOH + C2H5OH
This method is particularly useful for the preparation of higher fatty acids from oils and fats, which are triesters of glycerol.
C6H5COOC2H5 2 HO,H + → ←
C6H5COOH+C2H5OH
C6H5CH2OH HBr → C6H5CH2Br KCN →
C6H5CH2CN 2 HO,H + ∆ → C6H5CH2COOH
CH3CONH2 3 HO + ∆ → CH3COOH+ NH3 CONH2 3 HO + ∆ → COOH +NH3
10.7.4 From Alkylbenzene
Aromatic carboxylic acids can be prepared by oxidation with chromic acid (or) acidic (or) alkaline KMnO 4. The entire side chain is oxidised to the carboxyl group irrespective of length of the side chain. Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected. CH3 4 KMnOKOH Heat →
OOK
10.7.5 From Acyl Halides and Anhydrides
Acid chlorides on hydrolysis with water or base hdrolysis followed by acidification and anhydrides on hydrolysis with water, carboxylic acids are formed.
RCOCl 2 HO → RCOOH + HCl 2 + 3 HO OH HO
RCOClRCOOCl | RCOOH
(C6H5CO)2O 2 HO → 2C6H5COOH
C6H5COOCH3 2 HO →
C6H5COOH+CH3COOH
10.7.6 Acetic Acid Is Prepared by the Following Methods
From methyl alcohol and carbon monoxide:
In the presence of rhodium or cobalt, methanol combines with carbon monoxide and forms acetic acid.
CH3OH + CO CoorRh ,Pressure ∆ → CH3COOH
From acetaldehyde:
Acetic acid is commercially prepared by the oxidation of acetaldehyde with air in the presence of manganese acetate catalyst.
CH3CHO+ 1 2 O2 32 air Mn(OCOCH) → CH3COOH
From ethyl alcohol:
Vinegar is 6–10% aqueous solution of acetic acid. It is obtained by fermentation of liquors containing 12 to 15% ethyl alcohol. Fermentation is done by bacterium Mycoderma aceti in the presence of air at 30–35°C. This process is termed acetous fermentation.
CH3CH2OH + O2→ CH3COOH + H2O
Q. When a compound A of the formula C2H5Br reacts with magnesium in the presence of ether to form Grignard reagent which upon reaction with dry ice followed by acidification, is converted into a carboxylic acid, B. Two moles of B can also be given by one mole of C
upon its ozonolysis. Identify the compounds, A, B and C.
Sol. 1.CO2 Mg 25 25 25 ether 2.acid B A CHBrCHMgBrCHCOOH →→− .
Ozonolysis of an Alkyne can produce carboxylic acid 2 25 2525 CHCCCHCHCOOH −≡−→−
Therefore, A is Ethylbromide, B is propanoic acid and C is 3–hexyne.
Try yourself:
When a alkyl halide of formula, CH 3 Br is converted into Grignard reagent by treating it with magnesium in ether and finally made to react with dry ice followed by acidification, a carboxylic acid, A is formed. Two moles of A is formed upon ozonolysis of an alkyne, B. What is the systematic name of the B?
TEST YOURSELF
1. Identify ‘C’ in the following sequence of reactions
(1) CH3CH2CONH2
(2) CH3CN
(3) (CH3CO)2O
(4) CH3COOH
2. 1-butyne on oxidation with hot alkaline KMnO4 would yield which of the following as end product?
(1) CH3CH2CH2COOH
(2) CH3C2COOH
(3) CH3CH2COOH+CO2+H2O
(4) CH3CH2COOH+HCOOH
3. () () 24
The product ‘B’ is (1) acetic acid
(2) acetone
(3) acetaldehyde
(4) formic acid
4. Which one of the following reactions will not yield propionic acid?
(1) CH3CH2CCl3+OH−/H3O+
(2) CH3CH2COCH3+IO−/H3O+
(3) CH3CH2CH2OH+KMnO4/H+
(4) CH3CH2CH2Br+Mg, CO2 dry ether/HO+
5. Which one of the following functional groups undergoes hydrolysis with alkali to yield an acid group?
(1) -CN (2) -CHO
(3) -COCH3 (4) -Br
6. Oxidation of primary alcohols finally gives (1) aldehydes
(2) ketones
(3) carboxylic acids
(4) esters
7. In the reaction, Ethanol PI33HO KCN ABC; + ∆ →→→ here C is (1) acetamide (2) propionamide (3) propanoic acid (4) acetic acid
8. () 2 2 ClOnemoleRedP 3 HO/H alc.KCN CHCOOH X YZ; + → → → (1) Lactic acid
(2) Propionic acid
(3) Malonic acid (4) Fumaric acid
9. Hydrolysis of acetamide produces (1) acetic acid
(2) acetaldehyde
(3) methyl amine
(4) formic acid
10. Z in the following sequence is 3 3 CHCl Zn dust anhyd.A/Cl 4 Alkaline Phenol X YZ. KMnO
(1) Toluene (2) Benzene
(3) Benzoic acid (4) Benzaldehyde
Answer Key
(1) 4 (2) 3 (3) 1 (4) 4
(5) 1 (6) 3 (7) 3 (8) 3
(9) 1 (10) 3
10.8 PROPERTIES OF CARBOXYLIC ACIDS
Carboxylic acids are stronger acids than alcohols and phenol. In their properties –COOH group is involved.
10.8.1 Physical Properties
Aliphatic carboxylic acids up to nine carbon atoms are colourless liquids at room temperature with unpleasant odour.
The higher acids are wax like solids. Carboxylic acids are higher boiling liquids than aldehydes, ketones, alkyl halides, ethers, alkanes and even alcohols of comparable molecular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding. Even in vapour state, the hydrogen bonds are not broken completely. In liquid state, carboxylic acids are polymeric. In the vapour state or in non-aqueous solutions, they are dimeric.
and miscible with water in all proportions. 100% acetic acid free of water is called glacial acetic acid. Since the mp of anhydrous acetic acid is 17 0C, it is solid in a refrigerator and looks “icy”, hence the name.
Structure of Carboxyl Group
In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120 0 . The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure shown below:
10.8.2 Chemical Properties
In chemical reaction of Carboxylic acids, O–H bond, C–O bond and C–C bond of the acids are involved.
Reactions Due to the Fission of O–H Bond
Carboxylic acids release hydrogen with active metals like sodium. Similar to phenols.
2RCOOH + 2Na→ 2RCOONa + H 2↑
2CH3COOH + 2Na2→CH3COONa + H2↑
Carboxylic acids form salts with alkalies like sodium hydroxide, calcium hydroxide, etc.
Carboxylic acids up to four carbon atoms are highly soluble in water due to the formation of hydrogen bonds with water. Solubility of acid decreases with an increase in the size of hydro-phobic alkyl group. Carboxylic acids are also soluble in less polar organic solvents like benzene, chloroform, ether, etc. The simplest aromatic carboxylic acid, benzoic acid is nearly insoluble in cold water.
RCOOH + NaOH→RCOONa + H 2O
CH3COOH + NaOH→CH3COONa + H2O
2CH3COOH + Ca(OH)2 →
(CH3COO)2Ca + 2H2O
Unlike phenols, carboxylic acids react with weaker bases like carbonates and bicarbonates to evolve carbon dioxide. This reaction is used to detect the presence of carboxyl group in an organic compound.
2RCOOH + Na2CO3→
Acetic acid is a colourless pungent liquid with a boiling point of 118°C. It is sour to taste
2RCOONa + H2O + CO2↑
2CH3COOH + Na2CO3→
2CH3COONa + H2O + CO2↑
RCOOH + NaHCO3 →
RCOONa + H 2O + CO2↑
CH3COOH + NaHCO3 →
CH3COONa + H2O + CO2↑
Acids stronger than carbonic acid release carbon dioxide from carbonates or bicarbonates. This reaction is characteristic of carboxylic acids and they can be distinguished from other compounds. Carboxylic acids can be separated from other compounds by dissolving in NaHCO3 or Na2CO3. The sodium salt of acid formed regenerates acid on adding HCl.
Reactions Due to the Fission of C–O Bond
Formation of esters: Carboxylic acids react with alcohols and phenols in the presence of conc. H2SO4 or HCl gas catalyst and form esters. This is called Fischer’s esterification. It is a reversible reaction. Esters have pleasant fruity smell.
RCOOH + HOR HSO24
CH3COOH + HOC2H5
Mechanism
R–COOR + H2O
Formation of Anhydrides
On heating with a dehydrating agent like phosphorus pentoxide, carboxylic acids form acid anhydrides.
2RCOOH 25 2 PO HO → RCOOCOR + H2O
2CH3COOH 25 2 PO HO → CH3COOCOCH3 + H 2O
Formation of Acid Chlorides
Carboxylic acids form acid chlorides with thionyl chloride or phosphorus pentachloride or phosphorus trichloride. Thionyl chloride is the preferred reagent.
CH3COOH + PCl5→ CH3COCl + POCl3 + HCl
3CH3COOH + PCl3→3CH3COCl + H3PO3
CH3COOH +SOCl2→CH3COCl + SO2 + HCl
Reaction with NH3
When heated with ammonia, carboxylic acids form amides.
RCOOH + NH3 → ← 4 RCOONH +
RCONH2 + H2O
CH3COOH + NH3 → ← CH3CONH2 + H2O
Reactions Involving –COOH Group
Reduction: On reduction with lithium aluminium hydride or diborane, carboxylic acids form primary alcohols. Sodium borohydride does not reduce the carboxyl group.
RCOOH 426 3 1)LiAlH|etherorBH 2)HO + → RCH2OH
CH3COOH 4 LiAH
l CH3CH2OH
Oxidation: Acetic acid is highly resistant to oxidation, but on prolonged heating with oxidising agents finally produces carbon dioxide and water.
Reactions Involving Alkyl Group of Acid
In reactions of salts of carboxylic acids, many bond rearrangements are possible,
The a –hydrogens of a carboxylic acid are substituted by chlorine or bromine atoms when the acid reacts with Cl 2 or Br 2 in the presence of red phosphorus. This reaction is called Hell–Volhard–Zelinsky (HVZ) reaction. In this reaction, a -halocarboxylic acids are formed.
RCH2COOH + Cl2 2 (i)redP (ii)HO → RCHClCOOH + HCl
Acetic acid reacts with chlorine in the presence of red phosphorus to give monochloro-, dichloro- and trichloro acetic acid.
CH3COOH + Cl2 redP → ClCH2COOH + HCl
CH2ClCOOH +Cl2 redP → CHCl2COOH + HCl
CHCl2COOH + Cl2 redP → CCl3COOH + HCl
Reaction of Salts of Acid
Salts carboxylic acids undergo the following reactions
Decarboxylation
Carboxylic acids undergo decarboxylation when their sodium salts are heated with soda lime, and form hydrocarbons. The hydrocarbon formed will have one carbon less than the acid from which it is formed.
RCOO–Na+ + NaOH CaO ∆ → RH + Na2CO3
CH3COO–Na++NaOH CaO ∆ → CH4+Na2CO3
C6H5COO–Na++NaOH CaO ∆ → C6H6+ Na2CO3
Kolbe’s Electrolysis
When the aqueous solution of sodium salt of an acid is subjected to electrolysis, a hydrocarbon having twice the number of carbon atoms present in the alkyl group of the acid is formed. In Kolbe’s reaction, we also get alkane and alkene as disproportionation product.
2RCOO–Na++2H2O Electrolysis → 22 anodecathode
2CH3COONa + 2H2O Electrolysis →
CH3–CH3 + 2CO2 + 2NaOH + H2
Ring Substitution
Aromatic carboxylic acids undergo electrophilic substitution reactions. Carboxyl group is meta directing and deactivating. Aromatic carboxylic acids, however, do not undergo Friedel-Crafts reaction because the carboxyl group is strongly deactivating in nature. Hence nucleophilicity of benzene ring decreases.
With nitration mixture, benzoic acid forms m-nitrobenzoic acid. NO2
COOHCOO 3H 24 conc.HNO conc.HSO →
With chlorine, in the presence of ferric chloride, benzoic acid forms m-chloro benzoic acid as main product. Cl
COOHCOO 2H 3 C FeCl → l
Hunsdiecker Reaction
Bromo alkanes can be easily prepared by refluxing the silver salt of fatty acid with bromine in carbon tetrachloride.
CH3CH2COOAg + Br2 4 CCl/Reflux →
CH3CH2Br + CO2 + AgBr
This reaction undergoes free radical mechanism. The yield of the alkyl halide is primary > secondary > tertiary.
With I2, silver salts give esters instead of iodo alkanes. Reaction is known as BirnBaumSimonini reaction.
2RCOOAg + I2 4 CCl/ ∆ →
RCOOR + 2AgI + CO 2
10.8.3 Uses
■ Acetic acid is used as a solvent.
■ About 6–10% acetic acid is used as vinegar in cooking.
■ Formic acid is used in rubber, textile, dyeing, leather and electroplating.
■ Hexanedioic acid is used in the manufacture of nylon–6, 6, a polymer.
■ Esters of benzoic acid are used in the preparation of perfumes.
■ Sodium benzoate is used as food preservative.
■ Higher fatty acids are used for the manufacture of soaps and detergents.
Q. A carboxylic acid has the formula, C 4H6O2 Its structural isomer is formed when another carboxylic acid X reacts with enthylalcohol in the presence of a few drops of conc. H 2SO4 What is the compound, X?
Sol. Since, the acid, x reacts with C2H5OH to give the compound of the formula, C4H8O2, the x must have two carbon atoms. Therefore, the carboxylic acid is Acetic acid, CH 3COOH.
Try yourself:
A carboxylic acid of the formula, C 2H 4O 2(A) upon reduction with LiAlH 4 and an acid gives the compound, C2H6O(B) when the compounds A and B react with each other a product, C is formed. The structural of C has one primary alcoholic group and one isomer keto group. What is the systematic name of C?
Ans: 3-hydroxybutan-2-one
TEST YOURSELF
1. pka is least for
(1) BrCH2CH2COOH
(2) C6H5COOH
(3) HCOOH
(4) ClCH2−COOH
2. Propanoic acid is slightly weaker than acetic acid because (1) methyl group is electron with drawing (2) +I effect of C2H5 is more than –CH3
(3) the methyl group in acetic acid shows hyperconjugation.
(4) propanoic acid has two α-hydrogens.
3. Consider the following transformations ()()
The molecular formula of B is
(1) CH3–C(OH)ICH3
(2) ICH2–COCH3
(3) CHI3
(4) CH3l
4. The correct decreasing order of acidity of the following is
I) HCOOH II) CH3COOH
III) CH3CH2COOH IV) C6H5COOH
(1) (I)>(II)>(III)>(IV)
(2) (IV)>(I)>(II)>(III)
(3) (I)>(IV)>(II)>(III)
(4) (IV)>(I)>(III)>(II)
5. In the reaction, CH 3 COOH 5 4 PCl LiAlH AlC. KOH ABC →→→ , the product C is
(1) ethylene (2) acetyl chloride
(3) acetaldehyde (4) acetylene
6. Which of the following will not undergo Hell–Volhard Zelinsky (HVZ) reaction?
(1) CH3COOH
(2) (CH3)2CH−COOH
(3) CHCl2-COOH
(4) HCOOH
7. 4 LiAlH 3 CHCHCHCOOH−=−→ X The product X is (1) CH3CH2CH2CH2OH (2) CH3CH=CHCH2OH (3) CH3CH=CHCHO (4) CH3CH2CH2CHO
8. Acetic acid is treated with metallic sodium to form x and hydrogen. When X is treated with sodalime, Y and sodium carbonate are formed. ‘Y’ is (1) C2H6 (2) CH4 (3) CH3COONa (4) CH3CONH2
9. During Kolbe’s electrolysis of potassium acetate solution the anode products are, respectively,
CHAPTER
REVIEW
Nomenclature and Structure of Carbonyl Group
■ Aldehydes and ketones contain the carbonyl functional group.
■ According to IUPAC nomenclature, aldehydes are called alkanals and ketones are called alkanones.
■ Ketones having five or more carbon atoms exhibit metamerism.
Preparation of Aldehydes and Ketones
■ Primary alcohols on oxidation or on catalytic dehydrogenation give aldehydes and secondary alcohols on similar conditions yield ketones.
■ Dry distillation of calcium salts of fatty acids, along with calcium formate, give aldehydes.
■ Symmetrical ketones may be obtained when calcium salts of fatty acids alone are heated.
■ Vapours of fatty acids mixed with formic acid when passed over heated thoria or alumina or MnO give aldehydes.
(1) CH3−CH3, CO2
(2) CH3−CH3, H2
(3) CH3−CH2−CH2−CH3, CO2
(4) CH4, CH3−CH3
10. Which of the following carboxylic acids undergoes decarboxylation easily?
(1) C6H5-CO-CH2-COOH
(2) C6H5-CO-COOH
(3) 65 | OH CHCHCOOH
(4) 2 65 | NH CHCHCOOH
Answer Key
(1) 4 (2) 2 (3) 3 (4) 3 (5) 1 (6) 4 (7) 2 (8) 2 (9) 1 (10) 1
■ Vapours of a fatty acid alone give ketone on treating with Al2O3 or MnO.
■ Alkenes can be oxidised to carbonyl compounds by Wacker process by using aqueous palladium chloride in the presence of cupric chloride catalyst.
■ Depending upon the structure of alkene, different carbonyl compounds are obtained by the reductive ozonolysis.
■ Carbonyls are obtained by the hydration of alkynes or by alkaline hydrolysis of gem dihalides.
■ Reduction of acid chloride with hydrogen in the presence of Lindlar’s catalyst to give aldehydes is called Rosenmund reduction.
■ Ketones cannot be prepared by Rosenmund method.
Physical Properties
■ Carbonyl compounds are highly polar and boil at high temperatures than the weakly polar ethers of comparable molar masses.
■ Lower carbonyls are more soluble in water due to hydrogen bonding.
■ Due to larger size of hydrophobic alkyl group, higher c arbonyls are insoluble in water.
Chemical Reactions
■ The characteristic reactions of carbonyl compounds are nucleophilic addition reactions.
■ Aldehydes are more reactive than ketones. Aliphatic aldehydes are more reactive than aromatic aldehydes.
■ Ammonia reacts with aldehydes and ketones to form imines.
■ Carbonyl compounds condense with derivatives of ammonia, hydroxylamine, hydrazine, phenylhydrazine, 2, 4-dinitrophenyl hydrazine, semicarbazide to form the corresponding oximes, hydrazones, phenyl hydrazones, 2, 4–dinitrophenyl hydrazones and semicarbazones.
■ Carbonyl compounds react with PCl 5 or thionyl chloride to give gem dihalides.
■ Aldehydes are reduced to primary alcohols and ketones to secondary alcohols with LiAlH 4 , NaBH 4 or by catalytic hydrogenation.
■ Carbonyl group is reduced to methylene group, by Clemmensen or by WolffKishner reduction, thereby, carbonyl compounds are reduced to alkanes.
■ Aldehydes are easily oxidised to carboxylic acids by even mild oxidising agents like Tollen’s reagent, Fehling’s reagent and Benedict’s solution. These oxidation reactions are used to distinguish aldehydes from ketones.
■ The a–hydrogens in carbonyl compounds are acidic.
■ Carbonyl compounds having at least one a–hydrogen, undergo Aldol condensation.
■ Aldehydes with no a -hydrogen atom on reaction with concentrated alkali undergo Cannizzaro reaction in which aldehyde undergoes disproportionation to give alcohol and salt of carboxylic acid.
■ Compounds containing methyl keto group or which form these on treatment with halogens give haloform reaction.
Benzaldehyde
■ Aromatic carbonyl compounds undergo electrophilic substitution reactions.
■ Carbonyl group present in aromatic ring is meta directing and deactivating.
■ Benzaldehyde can be obtained by the oxidation of toluene with chromyl chloride followed by hydrolysis. This is called Etard reaction.
■ Benzaldehyde is also obtained from benzene by Gattermann–Koch reaction.
Nomenclature and Structure of Carboxylic Group
■ Carboxylic acids are compounds which contain –COOH group as functional group with general formula CnH2nO2 or C nH2n+1 COOH.
■ Trivial names are given based on source.
■ HCOOH is named formic acid because it is obtained by distillation of ants (Latin).
■ The IUPAC name of carboxylic acids is alkanoic acid.
■ Carboxylic acids release H+ ions in aqueous solution and so are acidic in nature
Preparation of Carboxylic Acids
■ Carboxylic acids are prepared by oxidation of primary alcohols and aldehydes.
■ Carboxylic acids are prepared by the action of CO2 on Grignard reagent followed by hydrolysis.
■ Carboxylic acids are prepared by the hydrolysis of alkyl cyanides and amides.
■ Methyl alcohol on treatment with CO in the presence of Co or Rh (catalyst) under high pressure and temperature gives acetic acid.
■ Acetic acid is commercially prepared by the oxidation of acetaldehyde by air in the presence of manganous acetate as catalyst
■ Acidic hydrolysis of esters gives directly carboxylic acids while basic hydrolysis gives carboxylates, which on acidification give the corresponding carboxylic acids.
■ Aromatic carboxylic acids are prepared by the oxidation of alkyl benzenes.
■ Acidified KMnO 4 or acidified K 2 Cr 2 O 7 oxidises alkenes to ketones and / or acids.
Properties of Carboxylic Acids
■ Carboxylic acids release H2 with Na, release CO2 with NaHCO3 or Na2CO3
■ Carboxylic acids dissolve in NaOH and are regenerated by HCl (not by CO 2).
■ Carboxylic acids form esters with alcohols, acid chlorides with PCl3, PCl5 or SOCl2 and amides with NH3.
■ On heating with Phosphorous pentoxide, Carboxylic acids give anhydrides, on reduction with LiAlH4, they give primary alcohols.
■ Carboxylic acids give aldehydes and ketones when their calcium salts are heated with calcium formate and alone respectively.
■ Decarboxylation of carboxylic acids gives hydrocarbons in the presence of soda lime.
■ Carboxylic acids with -hydrogen form -chloroacids with Cl2 in the presence of red phosphorus. This is called HVZ reaction.
■ A 6 to 10% dilute aqueous acetic acid is called vinegar. It is used in cooking.
■ Alcohols, phenols and carboxylic acids are acidic because they liberate hydrogen gas on reaction with sodium metal.
■ Alcohols have no reaction with NaOH but phenols and carboxylic acids react with NaOH. Thus alcohols are less acidic than phenols and carboxylic acids.
■ Phenols and carboxylic acids turn blue litmus to red litmus, alcohols cannot give this test.
■ Carboxylic acids decompose NaHCO3 and liberate CO2 gas.
■ Phenol cannot decompose NaHCO3. Thus phenols are less acidic than carboxylic acids.
■ Carboxylic acids are weaker than mineral acids. This can be proved from pKa values.
■ The substituents which stabilise the carboxylate ion will increase the acidic strength of carboxylic acids.
■ Electron withdrawing groups increase the acidic strength of carboxylic acids.
■ Electron donating groups decrease the acidic strength.
■ With increasing the electron withdrawing tendency of groups acidic strength increases.
■ Electron withdrawing tendency of some groups is,
CF3 > NO2 > CN > F > Cl > Br > I > C6H5
■ With increasing number of electron withdrawing substituents, acidic strength increases.
■ With increase in the distance of electron withdrawing group from -COOH, acidic strength decreases.
■ Alkyl substituents have electrons donating nature. With increasing the number of carbon atoms in alkyl substituent electron donating tendency increases and acidic strength decreases.
■ Direct attachment of C6H5-, CH2=CH- to carboxylic acids increases the acidity, due to greater electronegativity of sp 2 carbon, contrary to the decrease expected due to resonance effect.
■ In benzoic acid also electron withdrawing substituents increases the acidic strength but electron donating substituents like –CH3, –OH, –NH2, etc decreases the acidic strength.
■ The ortho isomer of every substituted benzoic acid is stronger than benzoic acid. This is called ortho effect.
■ Among p- and m-isomers, p-isomer has more acidic character than m-isomer for electron with drawing group.
■ The m-isomer is stronger acid than benzoic acid while p-isomer is weaker than benzoic acid for electron releasing group.
Exercises
NEET DRILL
Level-1
Nomenclature and Structure of Carbonyl Group
1. What is the IUPAC name of mesityl oxide?
(1) 4-methyl pent-2-en-3-one
(2) 3-methyl pent-3-en-2-one
(3) 4-methyl pent-3-en-2-one
(4) 3-ethyl pent-2-en-3-one
2. Which of the following exhibits tautomerism?
(1)
3. IUPAC name of C - CH2 - CH3
is
(1) propiophenone
(2) propanphenone
(3) 1-phenylpropanone
(4) ethylbenzenone
4. The correct IUPAC name of
OHC - CH 2 - CH - CH 2 - CHO
(1) 3-formyl pentane 1,5 dial
(2) propane-1, 2, 3-tricarbaldehyde
(3) 2-methyl formyl butane 1, 4 dial
(4) 3-formyl propane 1, 2 dicarbaldehyde
Preparation of Aldehydes and Ketones
5. In the following sequence reactions, of the final product (Z) is
(1) ethanol
(2) propan-2-ol
(3) propanone
(4) propanol
6. 2 24 Hg 3 dil. HSO CHCCHx + −≡→ (Carbonyl compound). The number of sigma, pi bonds and lone pairs of electrons in ‘x’ are respectively.
(1) 9, 2, 2 (2) 6, 1, 2
(3) 9, 1, 2 (4) 9, 2, 3
7. Ozonolysis of the following gives only CH3CHO
(1) CH3–CH = CH–CH3
(2) CH2 = CH – CH2–CH3
(3) CH3–C ≡ CH–CH3
(4) HC ≡ CH – CH2–CH3
8. Dry distillation of (CH3COO)2Ca gives (1) CH3CHO
(2) CH3COOH
(3) CH3COCH3
(4) C2H5–O– C2H5
9. CH3 COOC2 H5 1) DIBAL-H 2) H2 O 2) H2 O 1) LiAlH4 A B
Reagent required to convert B to A is (1) K2Cr2O7/H+ (2) PDC in CH2Cl2
(3) Cu, 300°C (4) both(2) and (3)
10. In the following reaction
the compound Z is
(1) benzoic acid (2) benzaldehyde (3) acetophenone (4) benzene
Physical Properties
11. Identify the correct statement.
A) Formaldehyde is a liquid.
B) Acetaldehyde is soluble in water.
C) Boiling point of ketones is greater than corresponding aldehydes.
D) Lower aldehydes have pungent smell.
(1) A, B, and D only (2) B and D only (3) A and C only (4) B, C, and D only
12. Which one of the following compounds will be most readily dehydrated?
(1)
Chemical Reactions
13. The increasing order of the rate of HCN addition to compounds I to IV is (I) HCHO (II) CH3COCH3
(III) C CH 3 O (IV) C O
(1) III < IV< I < II
(2) I < II < III < IV
(3) IV < II < I < III
(4) IV < III < II < I
14. The product obtained in the following reaction is specifically called as C = O CH2 - OH CH2 - OH + HCl gas
(1) acetal (2) hemiacetal
(3) ketal (4) cyanohydrin
15. Regarding the reaction of NaHSO 3 with carbonyl compounds, the correct statement is
(1) It reacts with all carbonyl compounds.
(2) Equilibrium will be towards left in its reaction with aldehydes.
(3) Equilibrium will be towards right in its reaction with ketones.
(4) Aldehyde sodium bisulphite derivatives are crystalline in nature.
16. Aldehydes and ketones give addition reaction with
(1) HCN (2) NaHSO3
(3) CH3MgX (4) All of these
17. Which of the following reagent is used to identify carbonyl group from other functional groups?
(1) Schiff’s reagent
(2) Fehling solution
(3) 2, 4 dinitro phenyl hydrazine
(4) Tollen’s reagent
18. CH 2 - CH2 - COOH
CH 2 - CH2 - COOH
Product (C) obtained is?
(1) CH3−CH = CH−CH3
(2) O
(3)
(4) N - NH 2
19. When acetone undergoes reduction presence of H2NNH2/KOH It is known as (1) Wolf-kishner’s reduction (2) Rosenmund’s reduction (3) Clemmensen reduction (4) Gattermann reaction
20. The appropriate reagent for the transformation
21. The reaction Pd/BaSO4 323 xylene CHCOCl+H CHCHO+HCl → is
(1) Stephen reaction (2) Rosemund reaction (3) Hoffmann reaction (4) Cannizzaro reaction
22. On reduction with LiAlH4, a ketone gives (1) 1° alcohol (2) 2° alcohol (3) 3° alcohol (4) alkane
23. Which of the following compounds not only give positive iodoform test but also give positive Fehling's test?
(1) H3C-CO-CH3
(2) C6H5CHO
(3) C6H5COCH3
(4) CH3CHO
24. Hex-4-ene-2-ol on treatment with PCC gives A. ‘A’ on reaction with sodium hypoiodite gives ‘B’, which on further heating with soda lime gives ‘C’. The compound ‘C’ is
(1) 2-Pentene
(2) Propionaldehyde (3) 2-butene
(4) 4-methylpent-2-ene
25. NaOH/I2 Ag 325 (yellow ppt) CHCOCH XY(g)→→ . In this sequence, the gaseous product Y is (1) ethyne
(2) ethane
(3) ethene
(4) propane
26. Which of the given reactions will not be able to form benzaldehyde as a product?
(1) Rosenmund reaction
(2) Etard reaction
(1) Zn(Hg), HCl (2) NH2NH2, OH (3) H2/Ni (4) NaBH4
(3) Gattermann-Koch reaction
(4) Cannizzaro reaction
27. In the reaction, 2 + 3 (i) SnCl+HCl conc. KOH 65 (ii) HO CHCN X Y+Z →→
Formation of X, Y, and Z are known by (1) Rosenmund reduction, Cannizzaro reaction
(2) Clemmensen reduction, Sandmeyer reaction
(3) Wolf-Kishner reaction, Wurtz reaction
(4) Stephen reaction, Canizzaro reaction
28. Which of the following will respond to Cannizzaro reaction?
(1) 2,2-Dimethylpropanal
(2) Acetaldehyde
(3) Propionaldehyde
(4) Cinnamaldehyde
29. Find the product formed for the given reaction.
/ 65 32 CHCHOHCCHCHO
(1) C2 H5 - CH = C - CHO CH3
(2) C6H5−CH2CH2CH2CHO
(3) C6 H5 - CH2 - C - CHO CH 3
(4) C6 H5 CH = C - CHO CH 3
30. Of the following which is the product formed when cyclohexanol undergoes aldol condensation followed by heating?
(1)
(2)
Correct statement is
(1) C is CH3CH2CHBrCHO.
(2) A is ethanamine.
(3) B is α, β unsaturated carboxylic acid.
(4) A → B is Aldol condensation.
32. Identify (X), (Y), and (Z) in the given reaction.
CH3 - CH - CH 2 - CHO X + Y z 3 - Hydraxybutanal OH
(1) X−HCHO, Y−CH3CHO, Z−KOH
(2) X−CH3CHO, Y−CH3CHO, Z−KOH
(3) X−CH3CH2OH, Y−HCHO, Z−H2SO4
(4) X−CH3CH2OH, Y−HCHO, Z−Dry ether
33. (i) O 3 (ii) Zn, H2 O NaOH C - CH3 O (A) (B) The reactant (A) is (1) (2) 3) (4) CH 2
34. Which of the following will not undergo aldol condensation?
(1) Acetaldehyde
(2) Propionaldehyde
(3) Trideutero acetaldehyde
(4) Benzaldehyde
35. Aldol condensation of (X) gives crotonaldehyde. dil NaOH 3 2XCHCHCHCHO
The number of π-bonds present in compound (X) is
(1) 1 (2) 2 (3) 3 (4) 4
36. Which of the following compound will give yellow precipitate with I2/NaOH and undergoes aldol condensation?
(1) H – CHO (2) C6H5−CHO (3) C6H5−CH2–CHO (4) CH3−CHO
37. ( 3 + 3 i) CHMgBr (i)Dil. NaOH Ä (ii)HO AR¾¾¾¾®¾¾¾¾®
4- methylpent – 3 –en – 2 – one. In the above reaction,'A' is
(1) propanone (2) ethanamine (3) ethane nitrile (4) ethanal
38.
.False statement is (1) D is crotonic acid.
(2) C is 2 – butenal.
(3) A is acetaldehyde. (4) B is β- hydroxyl butyraldehyde.
39. The product not formed when ethanal and propanal are heated in dilute alkali is (1)
(2)
(3) OHC (4)
40. Reaction of a carbonyl compound with one of the following reagents involves nucleophilic addition followed by the overall effect of -I and + R effect of elimination of water. The reagent is
(1) A Grignard reagent
(2) Hydrazine in presence of feebly acidic solution
(3) Hydrocyanic acid
(4) Sodium hydrogen sulphite
41. What is the product of the following reaction?
42. Regarding the compounds ‘A’ and ‘B’, dilute NaOH Ä 3 CH-CHO AB.→→ , the incorrect statement is
(1) ‘A’ has a chiral centre.
(2) ‘B’ shows geometrical isomerism.
(3) ‘A’ is a α–hydroxy carbonyl compound..
(4) ‘B’ is a α, β– unsaturated carbonyl compound.
43. The major product (P) in the following reaction is:
44. Major product ‘Y’ in following reaction sequence is:
45. Aromatic aldehydes react with primary amines to form ______.
(1) amide
(2) schiff’s base
(3) pyrrole
(4) pyridine
46. The number of compounds that not only gives yellow precipitate with NaOH + I 2 but also give red precipitate with Fehling’s reagent is
A) C2H5OH
B) CH3CHO
C) CH3COCH3
D) C6H5CHO
E) C6H5CH2CHO
(1) 4 (2) 3 (3) 2 (4) 1
47. CH3CHO and C6H5CHO can be distinguished by
(1) Baeyer's reagent (2) Tollens reagent (3) Schiff’s reagent (4) I2 + NaOH
Benzaldehyde
48. Reaction between benzaldehyde and acetophenone in presence of dilute NaOH is known as
(1) cross aldol condensation (2) aldol condensation (3) Cannizzaro reaction (4) cross cannizzaro reaction
49.
. The IUPAC name of the cross condensation product X is (1) benzalacetophenone
(2) 1,3 – diphenyl propanone–1
(3) 1,3 – diphenyl prop -2-en-1-one (4) 1,3 – diphenyl prop-1-en-3-one
Nomenclature and Structure of Carboxylic Group
50. Which of the following compounds does not have a carboxyl group?
(1) Methanoic acid (2) Ethanoic acid
(3) Picric acid (4) Benzoic acid
51. Which of the following does not contain the – COOH group?
(1) Ethenoic acid (2) Picric acid
(3) Valeric acid (4) Lactic acid
Preparation of Carboxylic Acids
52. Which of the following can not be oxidised to give carboxylic acid? (1)
53. The oxidation of toluene to benzaldehyde by using chromyl chloride is called as (1) Etard reaction
(2) Riemer-Tiemann reaction
(3) Wurtz reaction
(4) Cannizzaro reaction
54. Isobutyraldehyde on reaction with formaldehyde and K2CO3 gives compound ‘A’. Compound ‘A’ reacts with KCN and yields compounds B. Which on hydrolysis gives a stable compound ‘C’. The compound ‘C’ is
(1) CH CH HO CH CCHCOOH OH 3 3 2 | | |
(2) HO CH CH CH CH COOH CH OH 22 3 ||
(3) HO
55. dry ether 65 CHBr+MgA →
+ 3 2 HO CO BC→→ . IUPAC name of C is
(1) benzene carboxylic acid
(2) benzene carbaldehyde
(3) phenyl methanol
(4) phenyl ethanoic acid
56. + 3 4 HO KMnO+KOH Ä Toluene AC
+ 3 4 HO KMnO+KOH Ä n-propyl benzene PQ→→
(1) A and P are different, but C and Q are same.
(2) A and P are different, C and Q are also different.
(3) A and P are same, C and Q are also same. (4) C and Q are benzaldehydes.
57. Identify Z in the following, reaction sequence. + 25 2 PO HO/H Ä 34 CHCOONHXYZ →→→
(1) CH3CH2CONH2
(2) CH3CN
(3) (CH3CO)2O
(4) CH3COOH
Properties of Carboxylic Acids
58. The major product ‘Y’ in the following reaction is Ph
59. Consider an esterification of isotopically labelled carboxylic acid CH3 - C - OH + CH3 CH2 OH H+ O 18 A+B. A and B respectively are (1) CH 3 - C - OC2 H5 ; H2 O
(2) CH3 - C - OC2 H5 ; H 2O18
(3) CH3 - C - OC 2H 5; H2 O
(4) CH3 - C - OC2H 5; H2 O18
CHAPTER 10: Aldehydes, Ketones and Carboxylic Acids
60. The labelled O18 will be in _____after the completion of the reaction.
O - H
(1) H2O (2) Methyl benzoate (3) Both (1) and (2) (4) Benzoic acid
61. 2 Br/P 3 CH-COOH(A) → + NaCN HOH/H (B)(C)→→
The product (C) will be
(1) CH 2 COOH COOH
(2) CH 2 CH2 COOH COOH
(3) CO O CH2 CH 2 CO
(4) CH CO CH 2 CO O
62. COOH
2 I, NaHCO3 Major product(P). The product (P) is → (1) I O O (2) I I COOH (3) O O I (4) O O I
63. 2 SOCl 33 Äpyridine, CHCOOHA+CHCOCl+HCl → . The product (A) of the reaction is (1) SO2 (2) SO3 (3) H2S (4) CH3COOCH3
64. The correct order of acidic strength of the following is (i) COOH (ii) COOH NO 2 (iii) NO2 COOH (iv) COOH NO 2 (1) iii > iv > i > ii (2) ii > iv > iii > i (3) i > iv > iii > ii (4) iv > iii > i > ii
65. Which of the following acid will form an (a) anhydride on heating and (b) acid imide on strong heating with ammonia?
(1) COOH COOH
(2) COOH COOH
(3) COOH COOH
(4) OH COOH
66. Ä 2 KOBr PhCONHB → . The product (B) is (1) PhNHCOOMe (2) PhNH2 (3) PhNHCOOPh (4) C6H5–NO2
67. NMe2 O O (1) LiAlH4(excess)/ ether (2) H2 O (Z)
The major product of the given reaction is (1) NMe 2 OH O
(2) NMe2 OH O (3) NMe 2
4) NMe 2 OH O
Level-2
Nomenclature and structure of Carbonyl Group
1. IUPAC name of Isobutyraldehyde is (1) butanal (2) methyl propanal (3) ethyl ethanol (4) methyl butanal
2. Which of the following pairs represent metamers?
(1) C H CH 3 OH H 2C O C H (2) ph C CH3 O C CH3 O ph (3) O O (4) O O
3. The formula of benzoin is (1) C6H5−CO−C6H5
(2) C6H5−CO−CHOH–C6H5
(3) C6H5−CH2−CHO (4) C6H5−CO−CH3
4. Incorrect IUPAC match among the following is (1) H2C = CH−CHO−prop-2-enal (2)
7. When 1,1-dichloropropane and 2,2-dichloro propane are reacted separately with aqueous potassium hydroxide solution, compounds A and B are formed. Both A and B gave the same product C on reduction using amalgamated zinc and HCl. Identify C. (1) Propyl alcohol (2) Isopropyl alcohol (3) Propyl chloride (4) Propane
(3) OHC - CH2 - CH - CH 2 - CHO CHO Butane - 1,2,3, trial
(4) O CH3 2 methyl cyclohexanone
Preparation of Aldehydes and Ketones
5. The reagent used to bring about the transformation of but-2-ene to acetaldehyde is (1) pyridinumchlorochromate
(2) O3, H2O and Zn dust (3) chromium trioxide (4) acidified dichromate
6. In this reaction
acetic anhydride is used (1) as a catalyst (2) as an oxidising agent (3) to form a non-oxidisable derivative of benzaldehyde
(4) to help the reaction to proceed smoothly
8. 3 Anhyd. AlCl 66 CHCOHCl XHCl++→+ . The compound X is (1) C6H5CH3 (2) C6H5CH2Cl (3) C6H5CHO (4) C6H5COOH
9. Which one of the following reactions is called Rosenmund’s reaction?
(1) Aldehydes are reduced to alcohols. (2) Acids are converted to acid chlorides. (3) Alcohols are reduced to hydrocarbons. (4) Acid chlorides are reduced to aldehydes.
10. Isopropyl alcohol H/KCrO227 + → final product.The final product is (1) propene (2) propanol (3) ethanal (4) ethanoic acid
Physical Properties
11. Among the following mixtures, dipole-dipole as major interactions are present in (1) KCl and water (2) benzene and carbon tetrachloride (3) benzene and ethanol (4) acetonitrile and acetone
12. n – pentane = A, Diethyl ether = B, Butanal = C, n – butyl alcohol = D. The correct increasing order of boiling point is (1) A < B < C < D (2) B < A < C < D (3) D > C > A >B (4) D > C > B > A
Chemical Reactions
13. The general name of the compound formed by the reaction between aldehyde and alcohol is (1) acetal (2) glycol (3) acetate (4) ester
14. Which of the following reactions is not an example for nucleophilic additionelimination reaction?
(1) C HH OH CH 3 SO3 Na NaHSO 3 C O H CH 3 +
(2) 32 CHCHONHOH + 32 CHCHNOHHO =−+
(3) 3 652 CHCHOCHNHNH + 3 652 CHCHNNHCHHO =−+
(4) 3332 CHCHONHCHCHNHHO +=+
15. CH CO CH O iBr ii CH MgBr eq 24 6 2 3 2 () () products is
(1) (2)
(3)
(4) All of the above
16. Which of the following is not a correct nucleophilic addition- elimination product formed from a carbonyl compound?
(1) With hydrazine ---- C = N - NH 2
(2) With phenyl hydrazine -----------------
C = N - NH
(3) With 2,4 dinitrophenyl hydrazine ----NO 2 O2 N
C = N - NH
(4) With semicarbazide --------------------
C = N - C - NH - NH2 O
17. () 3 HO NaCN 3 (HCl) 2 CHCOAB + ∆ →→ .
In the above sequence, 'A' and 'B' are (1) (CH3)2C(OH)CN, (CH3)2C(OH)COOH (2) (CH3)2 C(OH)CN, (CH3)2 C(OH)2 (3) CH3CHOHCN, (CH3)2 CH3COOH (4) (CH3)2 C(OH)CN, (CH3)2 C = O
18. 2 HO,H XRMgXY + +→→ . If 'Z' is 1° alcohol, ‘X’ is (1) HCHO (2) CH3CHO (3) RCHO (4) RCOR’
19. The following compound is more reactive towards nucleophilic addition reactions. (1) CH3COCH3 (2) HCHO (3) CH3CHO (4) C2H5CHO
20. O LiAlH4 Conc.H 2SO4 (X); O The product(X) of reaction is : (1)
OH (2)
(3)
(4)
CHAPTER 10: Aldehydes, Ketones and Carboxylic Acids
21. In the given reaction 1. CH 3MgBr 2. H3 O Br (X) O (X) will be (1) Br OMgBr (2) O (3) O (4) O 22. Me 2CuLi H3 O O Product The product is (1) O (2) O
24. The structure of major products A, B, and C in the following reaction sequence will be
, dil. HCl
product will be
25. In the following reaction: Carbonyl compound HCl MeOH acetal + , the rate of the reaction is higher for
(1) acetone as a substrate and methanol in excess.
(2) propanal as a substrate and methanol in stoichiometric amount
(3) propanal as a substrate and methanol in excess
(4) acetone as a substrate and methanol in stoichiometric amount
26. Acetone is treated with excess of ethanol in the presence of dry HCl. The product obtained is
(1) CH 3CH 2CH 2 - C - CH 3 O
(2) CH 3CH 2CH 2 - C - CH 2CH 2Cl O
(3) OH (CH 3)2 C OC2H 5
(4) (CH 3) 2C OC2 H5 OC2 H5
27. Consider the reaction:
RCHO + NH2NH2 → RCH = N–NH2 What type of reaction is this?
(1) Electrophilic addition-elimination reaction
(2) Free radical addition-elimination reaction
(3) Electrophilic substitution-elimination reaction
(4) Nucleophilic addition-elimination reaction
28. The reagent that can distinguish between benzaldehyde and acetaldehyde is
(1) Tollens reagent
(2) Fehling’s solution
(3) conc.HCl + anhydrous ZnCl 2
(4) 2, 4-DNP
29. Which among the following will give positive 2,4-DNP test?
(1) C6H5OH
(2) (CH3)3COH
(3) CH3OC2H5
(4) C2H5CHO
30. The major product of the given reaction is CHO
X in this reaction can be
(1) LiAlH4.(or) N2H4/KOH, ethylene glycol. heat
(2) Zn-Hg/ conc. HCl (or) NaBH 4.
(3) HI + Red P/ heat (or) LiAlH 4
(4) Zn-Hg/ conc. HCl (or)HI + Red P/ heat.
32. What is the major organic product obtained from the following reaction?
/Ni(1eq')
(1) 2- pentanone
(2) (E)-3- penten-2-ol (3) 2-pentanol (4) 4-hydroxy-2-pentanone
33. Which of the following reagent(s) is/are used for the reaction given below?
(1) Glycol/LiAlH4/H3O+
(2) Glycol/NaH/H3O+
(3) LiAlH 4 (4) NaBH4
34. Which of the following will not give iodoform test?
(1) Acetophenone (2) Ethanal (3) Benzophenone (4) Ethanol
35. Pentan-2-one and pentan-3-one can be distinguished by (1) iodoform test (2) silver mirror test (3) legal test (4) lucas test
36. NaOCl A + B
The products 'A' and 'B' are (1) CH3–CH2–CH2–CH2–COONa, CHCl3 (2) CH3–CH = CH–CH2–COONa, CHCl3 (3) CH3–CH=CH–CH3; CHCl3 + CO2 (4) CH3–CH2–CH2–CH3; CHCl3 + CO2
37. How many of the following not only give positive haloform test, but also give positive Fehling's test? A) CH3–CO–CH3 B) C6H5–CH2–CHO C) CH3–CHO D) C6H5–CHO E) C6H5–CO–CH3
(1) B and C only
(2) B, C and D only
(3) C only
(4) A, B, C and D only
38. HO H O HCOH NaOH
The total number of moles of formaldehyde used in the above reaction sequence is (1) 2 (2) 1 (3) 4 (4) 3
39. (1) O3 /Zn (2) Conc.KOH OH - HCO2 (-)k +
(B) Major HBr CCl4 (A)
The product (B) is (1) Br (2) Br (3) (4)
40. The major product formed in the following reaction is 1) KOH/MeOH 2) O
(1)
(2)
(3)
(4)
41. The number of products obtained in the following reaction is
(1) 1 (2) 3 (3) 2 (4) 4
42. Identify A and B from the following reactions 3 2 (i) O 33 (ii) Zn-HO I. CH-CH=CH-CH 2X → 3 2 (i)O 1.NaOH(dil) 2. Ä (ii) Zn-HO II. 2X Z A+B
(1) CH3−CHO + HCHO (2) CH3 CHO + CHO
(3) CH3−CH2−CHO + CH2O (4) CH 3 - C - CH 3 + CHO CHO O
43. Consider the following reaction sequence:
CHAPTER 10: Aldehydes, Ketones and Carboxylic Acids
45. Identify 'A' in the given chemical reaction.
47. The compound 'A' in the following reactions is:
46. In the following reaction, ‘A’ is
Br2 , hv 2) KOH(alc)
O3 , DMS
NaOH (aq)+
(1) C6 H5 - C - CH3 O
(2) C6H 5 - C - CH O CH 3 CH3 (3) C6 H5 - CH2 - C - CH3 O (4) C6 H5 - C - CH2 CH3 O
Benzaldehyde
48. A mixture of benzaldehyde and acetophenone on heating with dilute NaOH solution gives (1) benzophenone (2) benzalacetophenone (Chalcone) (3) phenyl benzoate (4) benzyl alcohol and sodium benzoate
49.OH,293 K 65653 CHCHO+CHCOCH X; →
IUPAC name of cross condensation product ‘X’ is
(1) benzalacetophenone
(2) 1, 3–diphenylpropanone–1
(3) 1,3–diphenylprop–2–en–1–one
(4) 1, 3–diphenylprop–1–en–3–one
Nomenclature and Structure of Carboxylic
Group
50. The IUPAC name of the compound is:
C6H5CH2COOH
(3) X : C 6H 5CH 2Br, Y : C 6H 5CH 2CN, Z : C6H5CH2COOH
(4) X : C 6H 5CH 2Br, Y : C 6H 5CH 2NC, Z : C6H5CH2COOH
55. Grignard reagents and organolithium compounds on addition to dry ice separately, followed by hydrolysis gives
(1) ketones and carboxylic acids, respectively. (2) carboxylic acids and ketones, respectively. (3) only carboxylic acids. (4) only ketones.
56. The acid D obtained through the following sequence of reactions is:
(1) 1, 2, 3-tricarboxypropane-2-ol
(2) 2-hydroxy propane-1, 2, 3-tricarboxylic acid
(3) 3-hydroxy-3-carboxypent-1, 5-dioic acid
(4) None of the above
51. The general formula of carboxylic acids is (1)CnH2nO2
(2)CnH2n+1O2
(3)CnH2n+2O2 (4)CnH2n-2O2
Preparation of Carboxylic Acids
52. 2 + 3 1) CO 65 2) HO CHMgBrP →
In the above reaction, the product 'P' is (1) phenol (2) benzoic acid (3) benzaldehyde (4) benzophenone
53. 227 + KCrO (O) 25 H CHOHXY. →→ What is 'Y' (1) CH3CHO (2) CH3COOH (3) CH3COOC2H5 (4) CH3COCH3
54. + 3 HO HBr KCN 652 Ä CHCHOHXYA
X, Y and Z in the above reaction is (1) X : C6H5CH2CH2Br, Y : C6H5CH2CH2CN, Z : C6H5CH2COOH (2) X : C 6 H 5 CHO, Y : C 6 H 5 CH 2 CN, Z :
(1) succinic acid
(2) malonic acid
(3) maleic acid
(4) oxalic acid
57. Carboxylic acids have higher boiling points than aldehydes, ketones and even alcohols of comparable molecular mass. It is due to their
(1) formation of intramolecular H-bonding (2) formation of carboxylate ion
(3) more extensive association of carboxylic acid via van der Waals forces of attraction
(4) formation of intermolecular H-bonding
Properties of Carboxylic Acids
58. In the following sequence of reactions, the compound C formed would be
(1) 2-propanol
(2) propanol
(3) propanoic acid
59. In the below set of reactions ethylbenzene yielded a product D. Here the product ‘D’ is
(1) CH3COOC2H5 (2) CH3CHO (3) CH3COOH (4) C2H5OH
61. Consider an esterification of isotopically labelled carboxylic acid + o 1 I H 3 I 8 32 CH--OH+C A C HCHOH → and B. A and B, respectively are (1) C OC2H5 18 + H2O CH3 O (2) C OC2H5 18 18 + H2O CH3 O (3) C OC2H5 18 + H2O CH3 O (4) C OC2H5 18 + H2O CH3 O
62. Which of the following is correct? (A) NaOHCaO 3 33 Heat CHCOONa CHCH + →− (B) Cl Cl2/Red.P 32 3 H2O I CHCHCOOH-CH-COOH C →
(C) NO2 Conc.HNO 3 Conc. H 2SO4 COOH COOH (D) Br COOH Br2/FeBr 3 COOH
(1) only A, B (2) only A, B, D (3) only B (4) only A, B, C, D
63. The major product of the following reaction is
64. In the following sequence of reactions:
the product ‘C’ is (1) C6H5COOH (2) C6H5CH3 (3) C6H5CH2OH (4) C6H5CHO
65. The major products 'P' and 'Q' of the following reaction sequence are
66. An organic compound [A], with a molecular formula C10H20O2 was hydrolysed with dilute sulphuric acid to give a carboxylic acid [B] and an alcohol [C]. The oxidation of [C] with CrO3–H2SO4 produced [B]. Which of the following structures are not possible for [A]?
(1) CH3 CH2 CH2 COO CH2 CH2 CH2 CH3 CH3 (2) CH3 - CH2 - CH - COOCH 2 - CH - CH 2CH 3 CH3 CH3
(3) CH 2 - CH - CH2 - CH 2-O - CO - CH2 - CH - CH 3 CH 3 CH 3
(4) (CH3)3–C–COOCH2C(CH3)3
CHAPTER 10: Aldehydes, Ketones and Carboxylic Acids
FURTHER EXPLORATION
1. The major product of the following reaction is O CN O (i) DIBAL - H (ii) H3 O
(2)
(4)
2. The major products of the following reaction are:
CH 3 - CH - CH - CH3 (i) KOt - Bu/ (ii) O3 /H 2O2 OSO2CH 3
+
4. The product 'P' in the above reaction is O O
DIBAL.H Toulene P
5. In the given reaction product (s) would be O
(1) O COOO CH2 OH and
MATCHING TYPE QUESTIONS
1. Match Column-I with Column-II Column-I (Common name) Column-II (IUPAC name)
(A) Cinnamaldehyde (p) 2-hydroxy benzaldehyde
(B) Valeraldehyde (q) 3-phenyl prop-2enal
(C) Acetophenone (r) pentanal
(D) Salicylaldehyde (s) Prop-2-enal (t) 1-phenyl ethanone
(A) (B) (C) (D)
(1) q t r s
(2) q r t p
(3) r q p t (4) r p q t
2. Match Column I with Column II. Column I (Reaction) Column II (Name of Reaction)
(A) CO, HCl Anhyd. AlCl3 /CuCl (p) Hell– Volhard–Zelinsky reaction
(B) R - C - CH3 + NaOX O (q) Gattermann–Koch reaction
(C) R - CH2 OH + R'COOH Conc. H2 SO4 (r) Haloform reaction
(D) R - CH 2COOH (i) X 2/red P (ii) H2 O (s) Esterification
(A) (B) (C) (D)
(1) q r s p
(2) s p q r
(3) r q p s
(4) p s r q
3. Match Column I with Column II Column I (Reaction) Column II (Reagent used)
(p) Anhydrous ZnCl2
(q) C2H5O(C) C6
(r) Red P
(s) LiAlH 4
(A) (B) (C) (D)
(1) q r p s
(2) r s p q
(3) p q r s
(4) q r s p
4. Match Column I with Column II
Column I (Reaction) Column II (name of reaction)
(A) R - C - Cl RCHO O (p) Aldol condensation
(B) C6 H5 NH 2 C6 H5 NC (q) Carbyl amine reaction
(C) CH3 CHO CH3 CHCH2 CHO OH (r) RiemerTiemann reaction
(D) C6H 5OH C6 H4 (OH)CHO (s) Rosenmund’s reaction (t) Kolbe’s electrolysis
(A) (B) (C) (D)
(1) s q p t
(2) s q p r
(3) s r p t
(4) s r p q
5. Match Column I with Column II
Column-I (Reactant) Column II (Test)
(A) H - C - H O (p) Compound reacts with Lucas reagent and gives immediate turbidity
(B) OH (q) Compound reacts with alcohol in the presence of acid and gives fruits colour
(C) CH3 - C - OH O (r) The compound reacts with ammonical AgNO3 and gives silver mirror
(D) H3 C CH 3 OH (s) The compound reacts with I2/NaOH and gives yellow CHI3 precipitate
(A) (B) (C) (D)
(1) s r q p
(2) r s p q
(3) r s q p (4) q r p s
6. Match Column I with Column II
Column I (Example) Column II (Reaction) (A)
(p) HVZ reaction (B) R - CH2 - COOH R - CH - COOH Br Br2 /Red p R - CH2 - COOH R - CH - COOH Br Br2 /Red p (q) Rosenmund’s reduction
(r) Cannizzaro’s reaction
Pd-C/BaSO 4 CH3 - C - H
3 - C - Cl +H2 O Pd-C/BaSO 4 CH3 - C - H O (s) Friedel-crafts acylation
(A) (B) (C) (D) (1) r s p q (2) r p q s (3) p r s q (4) r p s q
7. Match Column I with Column II
Column I (Reaction)
Column II (Process)
(A) CrO2 2 RCHOH−−→ CrO2 2 RCHOH−−→ (p) Dehydrogenation
(B)
CH3 - C - OH Cu 300 oC
CH 3 CH3 (q) Oxidation
(C) MnO2
22 CHCHCHOH=−−→ MnO2
22 CHCHCHOH=−−→ (r) Dehydration
(D)
CH3 - C - OH CH 3 CH3 20%H 3 PO4 358K (s) Elimination reaction
(A) (B) (C) (D)
(1) p,r p s q,s
(2) q,s p s p,r
(3) q,p s,r p,q s,r
(4) s p r s,r
STATEMENT TYPE QUESTIONS
Each question has two statements: statement I (S-I) and statement II (S-II)
(1) if both statement I and statement II are correct
(2) if both statement I and statement II are incorrect
(3) if statement I is correct, but statement II is incorrect
(4) if statement I is incorrect, but statement II is correct
1. S-I : Para nitro phenol has higher boiling point than ortho-nitro phenol.
S-II : Para nitro phenol has inter molecular hydrogen bonding. Ortho nitro phenol has intra molecular hydrogen bonding.
8. Match Column I with Column II
Column I (Reaction) Column II (Reagent) (A) (p) PCC (pyridinium chlorochromate)
(B) H3C H3C H H OH
O (q) Cu/573 K
O (r) K2Cr2O7+dil. H2SO4/293K (D)
C
(s) KMnO4/ H+/293K (t) H3PO4/358K
(A) (B) (C) (D)
(1) rt qs pq q
(2) rs pq pqrs qt
(3) s qt rs t
(4) qt q qr qs
2. S-I : Formaldehyde is more reactive than benzaldehyde for a nucleophilic addition reaction.
S-II : Formaldehyde is more volatile than benzaldehyde.
3. S-I : Boiling point of propanone is greater than that of propanal.
S-II : Ethanal is a functional isomer of ethylene oxide.
4. S-I : Aldehydes are more reactive than ketones.
S-II : Nucleophilic addition reaction in carbonyl compound 1
Steric hindrance ∝ and α positive
charge at the carbon of carbonyl group.
5. S-I : p-Methoxybenzaldehyde undergoes nucleophilic addition more readily than p-nitrobenzaldehyde.
ASSERTION AND REASON QUESTIONS
In each of the following questions, a statement of Assertion (A) is given, followed by a corresponding statement of Reason (R). Mark the correct answer as (1) if both (A) and (R) are true and (R) is the correct explanation of (A) (2) if both (A) and (R) are true but (R) is not the correct explanation of (A) (3) if (A) is true but (R) is false (4) if both (A) and (R) are false
1. (A) : Formaldehyde is a planar molecule. (R) : Carbon atom in formaldehyde is sp 2 - hybridized.
2. (A) : Phenoxide ion is more stable than carboxylate ion, hence phenol is more acidic than carboxylic acids.
(R) : The negative charge is delocalised over two electronegative oxygen atoms and one carbon in carboxylate ion.
BRAIN TEASERS
1. In the given sequence of reactions, the compound F(major) is
S-II : The carbon atom of the aldehyde group is more electrophilic in p-nitrobenzaldehyde than in p-methoxybenzaldehyde.
The
F(major) is.
3. (A) : Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses.
(R) : More extensive association of carboxylic acid molecules occur through intermolecular hydrogen bonding.
4. (A) : The boiling point of propanone is slightly higher than the boiling point of propanal.
(R) : Gram molar mass of propanal and propanone is the same.
5. (A) : Acetone can be converted into acetic acid by I2/NaOH.
(R) : Haloform reaction is given by α-methyl ketones.
2. H - C - HO
In this sequence of reaction, the compound(s) that gives iodoform reaction is/are
(1) Only A and B (2) Only A and C
(3) A, B, C, and D (4) Only B, C, and D
3. Consider the reaction (C2 H6 O) Cu/573k
Identify A, X, Y and Z.
(1) A = Ethanol, X = Acetaldehyde, Y = Butanone, Z = Hydrazone
(2) A = Methoxymethane, X = Ethanoic acid, Y = Butanone, Z = Hydrazone
(3) A = Methoxymethane, X = Ethanol, Y = Ethanoic acid Z= Hydrazone
(4) A = Ethanal, X = Ethanol, Y = But –2–enal, Z = semicarbazone
4. Arrange the following compounds in the decreasing order of keq for hydrate formation.
(1) C6H5COCH3
(1) 3 > 2 > 1 > 4 (2) 2 > 1 > 3 > 4 (3) 3 > 1 > 2 > 4 (4) 4 > 2 > 1 > 3
5. Match the Column-I with Column-II.
Column I (Reaction)
Column II (Products)
(p) Final product is unsaturated ketone or ketone
(C)
(q) Formation of sixmembered ring takes place
(r) Final product will give positive Tollens test
(s) Ring expansion takes place
(t) Final product gives positive test with Brady’s regent
(A) (B) (C) (D)
(1) s pqs pqt ps (2) qs pqt pqst pqst
(3) pqst ps pst pq (4) pqt qs qst qs
FLASH BACK (Previous NEET Questions)
1. Given below are two statements:
Statement I : The boiling points of aldehydes and ketones are higher than hydrocarbons of comparable molecular masses because of weak molecular association in aldehydes and ketones due to dipole-dipole interactions.
Statement II: The boiling points of aldehydes and ketones are lower than the alcohols of similar molecular masses due to the absence of H-bonding
In the light of the above statements, choose the most appropriate answer from the options given below:
(1) Both statement I and Statement II are incorrect
(2) Statement I is correct but statement II is incorrect
(3) Statement I is incorrect but statement II is correct
(4) Both Statement I and Statement II are correct
2. Match the List-I with List-II List–I (Products formed) List–II (Reaction of carbonyl compound with)
(A) Cyanohydrin (p) NH2OH
(B) Acetal (q) RNH2
(C) Schiff’s base (r) alcohol
(D) Oxime (s) HCN
(A) (B) (C) (D)
(1) q r s p
(2) p r q s
(3) s r q p
(4) r s q p
3. Which one of the following is not formed when acetone reacts with 2-pentanone in the presence of dilute NaOH followed by heating?
What is 'Y' in the above reaction?
(1) RCOO Mg+X
(2) RCOO X+
(3) (RCOO)2Mg
(4) R3CO Mg+X
CHAPTER TEST
Section-A
1. The IUPAC name of the following compound is Br CHO OH
(1) 5-bromo-3 hydroxy benzene carbaldehyde
(2) 3-bromo-5 formyl phenol
(3) 3-bromo-5- hydroxy benzene carbaldehyde
(4) 1-bromo-3 formyl-5-hydroxyl benzene
2. The IUPAC name of the given compound is:
(2) H3 C - C - C H2 O
(3) O O
(1) acetylcyclohexadiene
(2) (1-cyclohexa-2, 4-dienyl) ethanone
(3) 6-cyclohexa-1, 3-dienylethanone
(4) none of these
3. Which of the following statements about OHCH2CHOHCHO is not correct?
(1) It is an isomer of 1,3-dihydroxypropanone.
(2) It contains a tertiary alcoholic group.
(3) It has the same empirical formula as glucose.
(4) It can show optical isomerism.
4. Which of the following is an example of a conjugated diketone?
(1)
(1) CH3COCH3, CH3CHO
Here A and B are respectively
(2) CH3COCH2CH3, CH3CHO
(3) CH3COCH3, CH3CH2OH
(4) CH3CH2COCH3, CH3CH2OH
(1) I) SnCl2 + conc. HCl ; II) H3O+ (2) I) DIBAL – H; II) H2O
(3) dil. H2SO4
(4) both (1) and (2)
7. The catalyst in the Wacker process is (1) CuCl2
(2) PdCl2
(3) Cu2Cl2
(4) Pd
6. . Reagents that can be used in the given reaction is/are CH3C ≡ N → CH3CHO
8. The reagent used to convert allyl alcohol to acrolein is (1) KMnO4 (2) H2O2
(3) MnO2 (4) OsO4
(4) 5. CH3 COCl (CH 3)2 Cd +H2 Pd/BaSO 4 A
10.
The compounds ‘A’ and ‘B’ formed in the reaction are, respectively (1) carboxylic acid, carboxylic acid (2) ketone, aldehyde (3) ketone, ketone (4) ketone, amide
The product ‘B’ is (1) O (2) O H
(3) OH (4) OH
11. How many of the following reactions produce ketone?
a)
c) d)
(1) Two reactions
(2) Four reactions
(3) Three reactions (4) one reaction
12. Match the Column-I with Column-II.
Column-I (Reaction)
Column-II (Involves)
(A) CH CH OH Cu 32 (p) Dehydration
(B) CH CH OH CH Cu 3 3 | (q) Elimination (C) CH 3
CH3 Cu (r) Oxidation (D) Cu (s) Dehydrogenation (t) Neither oxidation nor reduction
(A) (B) (C) (D)
(1) qrs qrs pqt pqt (2) pqr rst qst pqt (3) pqs qst rst qst (4) qst pqr qrs rst
13. 4 3 24 HgSO CHCCH( A) dil. HSO −≡ 3 3 22 (1) BHTHF CHCCH (B) (2)HO/HO
(A) and (B) are major products and are differentiated by: (1) 2-4-DNP
(2) NaOBr (3) LiAlH 4 (4) NaHSO3
14. Arrange the following compounds in the increasing order of their boiling points:
CH 3 CHO, CH 3 CH 2 OH, CH 3 OCH 3 , CH3CH2CH3
(1) CH3CH2CH3 < CH3OCH < CH3CHO < CH3CH2OH
(2) CH3OCH < CH3CH2CH3 < CH3CHO < CH3CH2OH
(3) CH3OCH < CH3CH2CH3 < CH3CH2OH < CH3CHO
(4) CH3CH2OH < CH3OCH < CH3CH2CH3 < CH3CHO
15. The boiling point of a compound is a measure of inter molecular attractions. Boiling point is highest for
(1) OH
(2) O OH (3) O H
(4) O
16. Given below are two statements.
Statement-I : Cyanohydrin formation is reversible
Statement-II : Carbonyl compounds can be regenerated from NaHSO 3 Adducts on acidic hydrolysis but not on basic hydrolysis.
In light of the above statements, choose the correct answer from the options given below.
1) Both statement I and statement II are correct.
2) Both statement I and statement II are incorrect.
3) Statement I is correct but statement II is incorrect.
4) Statement I is incorrect but statement II is correct.
17. The most reactive among the following towards nucleophilic addition is (1) p-toulaldehyde (2) 4-nitrobenzaldehyde (3) benzaldehyde (4) acetophenone
18. A carbonyl compound reacts with HCN to form a cyanohydrin, which on hydrolysis forms a racemic mixture of a-hydroxy acids. The compound is (1) formaldehyde (2) acetaldehyde (3) acetone (4) diethyl ketone
19. The interaction of acetone with methyl magnesium chloride in the presence of water gives (1) isobutyl alcohol (2) tertiary butyl alcohol (3) n-butyl alcohol (4) sec-butyl alcohol
20. Which one of the following reagents react with both acetaldehyde and acetone?
(1) Fehling’s solution (2) Grignard reagent
(3) Schiff’s reagent (4) Tollens reagent
21. A sample of acetaldehyde contained some ethyl alcohol as an impurity. The reagent useful for the purification of CH 3CHO is (1) NaHCO3 (2) Na2CO3 (3) NaHSO3 (4) PCl5
22. What would be the major product of following reaction?
(2)
CHAPTER 10: Aldehydes, Ketones and Carboxylic Acids
(3) O O
(4) No reaction
H5
23. An organic compound C3H6O does not give a precipitate with 2,4-dinitrophenylhydrazine and also does not react with metallic sodium. It could be
(1) CH3CH2CHO
(2) CH2 = CHCH2OH
(3) CH3COCH3
(4) CH2 = CH–O–CH3
24. Match Column I with Column II .
Column I (Reaction) Column II (Reagent)
(A) CH3COOH → CH3CH2OH (p) AlH(i–Bu) 2 ; H2O
(B) RCOCH3→ COONa (q) B2H6;H3O+
(C) RCN → RCHO (r) NaOX
(D) RCOONa → RH (s) NaBH4
(t) NaOH+CaO, ∆
(A) (B) (C) (D)
(1) q r p t
(2) s r p t
(3) q r s t
(4) q r t s 25. CH 3COCl AlCl3 A Zn - Hg con.HCl B AlCl3 C Cl2
3 The correct structure is
26. The product formed in the following chemical reaction is:
- C - OCH 3
CH2 - CH 2 - OH
CH2 - C - CH 3 OH H CH 3 OH
OH O
CH2 - C - OCH3
CH2 - C - OCH 3 OH H CH 3 OH
27. What is the IUPAC name of the organic compound formed in the following reaction?
3 + 2 ° II (i) CHMgBr 33 (ii) HO/H CH-C-CH
MajorProduct →
(1) Pentanol - 2
(2) 3 – pentanol
(3) 2 – methyl but an – 2 – ol (4) 2 – methyl propan – 2 – ol
28. The proper combination of a substrate and a reagent in the preparation of iodoform is (1) CH3OH, Zn+HI
(2) C2H5OH, HI+Red P/Δ (3) CH3COOH, I2+Red P
(4) C2H5OH, Na2CO3+I2/Δ
29. Reagent used in Gattermann – Koch reaction is
(1) CO + HCl
(2) anhydrous AlCl3 (3) CuCl
(4) Both (2) and (3)
30. The product formed in the following reaction is
31. Structure of the compound whose IUPAC name is 3-ethyl-2-hydroxy-4-methyhex-3en-5-ynoic acid is (1) COOH
(2)
(3)
(4) COOH
32. + 3 HO dry 2 Ether RMgX+COYRCOOH →→ , What is 'Y' in the above reaction?
(1) RCOO2Mg (2) RCOO–Mg+X (3) R3COMgX (4) RCOO–X+
33. Mg NBS 653 dry ether CHCHAB →→ + 3 HO CNBr Ä CD,→→ ‘D’ is (1) o- bromo benzoic acid
(2) phenyl acetic acid
(3) p- bromo benzoic acid
(4) m- bromo benzoic acid
34. Each question has two statements.
Statement – I: Carboxylic acids are weaker acids than mineral acids.
Statement – II: Acetic acid is a moderate strong acid.
In light of the above statements, choose the correct answer from the options given below.
1) Both statement I and statement II are correct.
2) Both statement I and statement II are incorrect.
3) Statement I is correct but statement II is incorrect.
4) Statement I is incorrect but statement II is correct.
Section-B
35. Match List–I with List–II.
List – I (Reaction) List – II (Product )
(A) Rosenmund’s reaction (p) Bi phenyl
(B) ReimerTiemann reaction (q) α- halo carboxylic acid
(C) Fittig reaction (r) Aldehydes
(D) HVZ reaction (s) Salicylaldehyde
(A) (B) (C) (D)
(1) s t r q
(2) r s t q (3) s r t q
(4) r s p q
36. 2622 a) BH/THF 32 b) HO/OH CH-CH=CH A → PCC'X'BA→→ . ‘X’ cannot be (1) HI + Red P /150°C
(2) NaBH4
(3) LiAlH 4 (4) H2/Ni
37. The products formed in the following reaction 'A' and 'B' are O
A B H + [Ag(NO 3 )2 ] OH - NaBH4
(1) A = H O B = , H H OH CH 2OH
(2) A = B = , OH HH OH HH CH 2OH
(3) A = B = O , COOH COOH OH H HH (4) OH CH 2OH , A = B = O H COOH H H
38. H24 NaBH Cu 3 Pt 573 K CHCHOAB→→→ 3 2422 a) BH/THF Conc.HSO 443 K b) HO/OH C ®D E →→ .
In the above conversion, the compound ethyl alcohol is (1) A only (2) C and D only (3) B and C only (4) A, C and E only
39. Identify A in the following chemical reaction
40. Match Column I with Column II
Column I (Reaction) Column II (Product)
(A) RCN reduction → (p) 1° Amine
(B) RCN 2 (i) CHMgBr (ii) HO → (q) Alcohol
(C) RCN hydrolysis → (r) Ketone
(D) RCN HNO2 → (s) Acid
(A) (B) (C) (D)
(1) p r s q
(2) p,s q r s
(3) q r,p s p
(4) s q r p,r
41. Predict the major product of the following reaction sequence.
(1) CH3CH = CHCH2OH
(2) CH3CH2CH2CH2OH
(3) CH3CH2CH2CHO
(4) CH3CH = CHCHO
43. The final product (Y) formed in the reaction.
44. Match Column-I with Column-II is Column-I (Reagent) Column-II (Composition)
(A) Fehlings solution (p) AgNO3/ Ammonia solution
(B) Tollens reagent (q) CuSO4/OH–/ Rochelle salt
(C) Lucas reagent (r) Benzene sulphonyl chloride
(D) Hinsberg reagent (s) anhydrous ZnCl2/Con HCl
(A) (B) (C) (D)
(1) q r s p
(2) r p q s
(3) q p s r
(4) q p r s
45. Match the Column-I with Column-II.
Column I (Reaction)
(A) PhMgBr+(A)
Column II (Reactant)
H + → 1°alcohol (p) CH 3 - C - CH 2 - C - CH 3 O
(B) PhMgBr+(B)
H + → 2°alcohol (q) CH3 - C - CH3 O
(C) PhMgBr+(C)
H + → 3°alcohol (r) CH3 - C - H O
(D) PhMgBr D H (s) H - C - H O
(A) (B) (C) (D) (1) s r p q (2) s q r p
(3) s r q p (4) s r p r
46. O O O PhMgBr excess (A) + The product (A) is (1) Ph - C - Ph O
(2) Ph - C - Ph OH Ph
(3) Ph - C - O OH Ph
(4) Ph - C - O O
47. The IUPAC name of the compound ‘A’ in the following reaction is
O
i) DIBAL -H 32 25 i II i)HO 6 CHCH--OCH ' C 'A →
Compound A is
(1) 1-Ethoxyoctan-1-ol
(2) 1-octanol
(3) octanal
(4) 1-Decanol
48. X Cyclo Hexanol Cyclo Hexanone → X cannot be
(1) PCC (2) Collin’s reagent (3) DiBAL – H (4) K2Cr2O7/H+
49. Carboxylic acids have higher boiling points than aldehydes and ketones and even alcohols of comparable molecular mass. It is due to their
(1) formation of intramolecular H-bonding
(2) formation of carboxylate ion
(3) more extensive association of carboxylic acid via van der Waals forces of attraction
(4) foration of intermolecular H-bonding
50. Match Column I with Column II Column I (Reaction) Column II (Product) (A) 2 Hg,H HO HCCH ++
(B) (C) (D)
Further Exploration
Matching Type Questions
Statement Type Questions
Assertion and Reason Questions
Brain Teasers
Test
