Comparing the Reaction Pathways of Acetophenone and Hydroxyacetophenones in Nitration Reactions Nicole Wedad Khouryawad and Nannette M. Wachter Chemistry Department, Hofstra University, Hempstead, NY 11549-0151 Abstract
HNMR of 2-Hydroxyacetophenone After Nitration
GC-MS of 3-Hydroxyacetophenone After Nitration
The product obtained when acetophenones are heated with nitric acid in the presence of acetic anhydride varies depending on the substituent on the aromatic ring. Acetophenone and most substituted acetophenones generate a symmetrically substituted 3,4-dibenzoyloxadiazole-2oxide (dibenzoylfuroxans). However, hydroxy-substituted acetophenones undergo ring substitution under these same conditions. When reacting 2-hydroxyacetophenone with nitric acid, a mixture of two mono-nitration products and one dinitration product are obtained. Similarly, nitration of 3-hydroxyacetophenone yields multiple mono- and dinitration products. Curiously, heating 4-hydroxyacetophenone with nitric acid and acetic anhydride results in loss of the acetyl group and the formation of 2,4-dinitrophenol. The results from each reaction can be analyzed with both nuclear magnetic resonance and mass spectroscopy in order to compare the percent yields of each product from the different nitration’s.
Introduction During our investigations of furoxan formation by acetophenones treated with nitric acid, we observed that hydroxyacetophenones undergo electrophilic aromatic substitution with nitric acid resulting in multiple nitration products. The signals in the H NMR are relatively making it possible to calculate percent yield of each individual product from the nitration’s. Further analysis using GC-MS for the nitration products of 3-hydroxyacetophenone support our yield calculations.
Products Obtained From Nitration of Hydroxyacetophenones Percent Yield Calculations based on Integrated Areas of H NMR Signals HNMR of 3-Hydroxyacetophenone After Nitration
Discussion
O
NO2 HNO3
HO
4HOAce
HO (CH3CO)2O 60 oC, 30 min
NO2
NMR Analysis The products obtained from the nitration of hydroxyacetophenones can be analyzed using H NMR. After each reaction concluded, the solution was neutralized with 10% Na2CO3 and extracted with dichloromethane. After the solution was dried over Na2SO4, the solvent was removed, and the crude product was dissolved in deuterated acetone and placed in a 400 MHz NMR spectrometer. Delta version 5 was utilized to analyze all the spectra.
Our research demonstrates that the multiple nitration products resulting from the reactions of hydroxyacetophenones with nitric acid can be differentiated and identified by H NMR analysis. Mass spectrometry can assist in the identification of mono- and dinitration products. NMR Analysis demonstrated that nitration of 2-hydroxyacetophenone and 3-hydroxyacetophenone result in three major products, whereas heating of 4-hydroxyacetophenone with nitric acid in acetic anhydride must oxidize the the acetyl group into a carboxylic acid leading to decarboxylation.. When nitration of 2hydroxyacetophenone was conducted at room temperature, the reaction yielded monosubstituted products with the nitro group ortho or para to the hydroxyl group, as well as a disubstituted product where the nitro groups were ortho and para. Nitration of 3-hydroxyacetophenone under similar conditions results in a complicated mixture of mono- and dinitration products. Heating the reaction mixture yields primarily disubstituted products where the nitro groups were either both ortho to the hydroxyl group or ortho and para to it. Nitration of 4-hydroxyacetophenone yielded 2,4-dinitrophenol. Careful integration of the areas of the signals resulting from the nitrated products of the 2- and 3hydroxyacetophenones makes it possible to identify the signals produced by the hydrogens that correspond to a single nitration product in the reaction mixture. Once the signals have been assigned to individual nitration products, it is relatively easy to calculate the percent yield of each of the compounds since the NMR results were so clear, showing that this experiment can provide both qualitative measure and quantitative information. GC-MS analysis on the products from the nitration of 3-hydroxyacetophenone confirmed our results from the NMR by maintaining almost the same exact amount of percent yield of each product as we had already determined. printed by www.postersession.com