Preparation of borane‐tert‐butylamine complex, (CH3)3CNH2BH3 – Sample 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐IN THE HOOD‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Weigh 1.0 g (0.026 mol) of NaBH4 and 0.71 g (0.013 mol) of NH4Cl into a 125 mL Erlenmeyer flask. Add 15 mL of toluene into the flask to dissolve the solids. Add 2.5 mL (0.025 mol) of tert‐butylamine into the flask. While stirring, add 2 mL of water (drop by drop) into the flask and continue stirring for 10 minutes. (Exothermic reaction, observe the gas formations – what are they?) Heat the reaction mixture at ~90oC in a water bath for 10 minutes. (The reaction is exothermic but why do we have to heat the reaction mixture?) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐AT YOUR BENCH‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Add 2.5 g of Na2SO4 into the flask. Swirl the flask and let it stay for 5 minutes. (What is Na2SO4 used for?) Carefully decant solution into another 125mL Erlenmeyer flask. Rinse the solid in the reaction flask with 10 mL of toluene and decant the rinsed solution into the same flask. (Why?) Add 100 mL of petroleum ether into the solution flask and put the flask in an ice bath for 10 minutes. DO NOT shake the flask. (Why?) Collect the crystals of borane‐tert‐butylamine complex by vacuum filtration. Weigh the crystal and calculate %yield based on the limiting reagent. Measure melting point and take IR spectrum of the crystal. Weigh ~20 mg of the sample into an NMR tube for 1H NMR analysis.
Preparation of iodoborane‐tert‐butylamine complex, (CH3)3CNH2BH2I – Sample 2 Weigh 0.7 g (0.008 mol) of borane‐tert‐butylamine into a Schlenk tube. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐IN THE HOOD‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Flow N2 gas into the tube and continue flowing until all reagents are added. (Why?) Add 3 mL toluene. Carefully add 1 g (0.004 mol) of iodine portion wise (Why?) until the solution slightly turns brown. (What does this color change mean?) Add small amount of borane‐tert‐butylamine, until the solution turns clear. (What does this color change mean? Which reagent is limiting reagent?) Transfer ~0.3 mL of the solution into a pre‐weighed NMR tube, using a Pasteur pipet. Cap the Schlenk tube with a septum and the NMR tube with a cap and bring it to your bench. Add 0.5 mL of petroleum ether into the NMR tube to precipitate the product. Cap and gently shake the NMR tube. Let the solid precipitate and remove the solution by using a Pasteur pipet and re‐cap the NMR tube. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐AT YOUR BENCH‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Make a hole on a cap of the NMR tube. Attach the tube to a vacuum line and wait until the tube is no longer cold. (Why?) Reweigh the NMR tube to record the mass of the final product. Cap it with a normal cap and save for 1H NMR analysis.
Preparation of boronium cation, di‐(tert‐butylamine)boronium iodide, [(CH3)3CNH2∙BH2NH2C(CH3)3]I – Sample 3 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐IN THE HOOD‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Using a pipet, carefully add ~1 mL of tert‐butylamine into the Schlenk tube by using a Pasteur pipet until no more precipitate formed. (CAUTION: exothermic reaction, vapors of toxic amine formed!) Remove the mother liquor from the Schlenk tube by using a Pasteur pipet. Rinse the solid with 3 mL toluene. Swirl the tube and remove the liquid by using a Pasteur pipet. Vacuum the Schlenk tube by using a manifold, until the tube is no longer cold. Weigh the product and calculate %yield base on borane‐tert‐butylamine complex. Measure melting point and take IR. Weigh ~20 mg of the sample into an NMR tube for 1H NMR analysis.
Preparation of borane‐tert‐butylamine complex, (CH3)3CNH2BH3, from di‐(tert‐ butylamine)boronium iodide and sodium borohydride – Sample 4 Weigh 0.56 g (0.002 mol) of di‐(tert‐butylamine)boronium iodide and 0.16 g (0.004 mol) of sodium borohydride into a 125 mL Erlenmeyer flask. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐IN THE HOOD‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Add 10 mL of toluene. Add 1 mL of water. Stir for 20 minutes until no more gas formed. Carefully decant the solution into another 125 mL Eelenmeyer flask. Dilute it with 100 mL petroleum ether. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐AT YOUR BENCH‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Put the flask in an ice bath to precipitate the product Vacuum filter the product. Weigh and calculate %yield based on boronium cation. Measure melting point and take IR to compare with sample 1. Weigh ~20 mg of the sample into an NMR tube for 1H NMR analysis.