Claim: Relatively pure isoamyl acetate was isolated by elimination reaction as compared to the SN2 reaction. Evidence1: A flask containing isoamyl bromide (6 ml, 0. 050 mole) and potassium acetate (6 g, 0. 05 mole) in 10 ml of dimethyl formamide was positioned in a steam bath and then mounted on a magnetic stirrer. The mixture was heated and magnetically stirred simultaneously for two hours. A white precipitate was found at the bottom of the solution. The mixture was set to cool and 15 ml of cool water was then added to the mixture.
The entire precipitate dissolved in the mixture and the content of the flask now got transformed into a clear colorless solution. The mixture was then washed with 15 ml of ether. The lower, aqueous layer in the flask was drawn off and the ethereal was again washed by 5 ml of water. The ethereal was then dried using magnesium sulfate and the ethereal was then gravity filtered. The ether was completely removed by simple distillation1 using steam as a source of heat.
The residual crude isoamyl acetate was isolated by simple distillation using a flame as a heat source. Isoamyl acetate; 4. 721 g, 36. 3 mmole, 72. 6 % recovery, B. p= 137? C – 142? C (lit=142? C2). The isoamyl acetate was then tested by infrared spectroscopy (IR spectroscopy); C-H stretch: below 3000 cm, C=O stretch: 1750 cm, C-O stretch: 1250 cm (Appendix 1, 2) Discussion: Isoamly acetate was isolated by SN2 nucleophilic substitution method. It was observed that the Nucleophile, acetate ion directly displaced the bromide ion by substitution.
The experiment used potassium acetate rather than sodium acetate. Potassium is larger and less dense than sodium so that the acetate ions more readily take part in the reaction. DMF, a polar aprotic solvent, was used to destabilize the nucleophile that catalyzes the reaction by lowering energy. After the mixture was cooled, water was added to the mixture in order to avert a reverse reaction. The mixture was washed with ether in order to maximize the yield of the produce by the process of dehydration.
Any presence of water would cause the reverse reaction, thus minimizing the yield. isoamly acetate was also isolated by elimination reaction, technically termed as fisher esterification. The fisher esterification was favored over SN2 reaction in this experiment. A flame was used as a heat source in the elimination reaction while a steam was used as a heat source in the Sn2 reaction. At higher temperatures, molecules acquire enough energy to climb the energy barrier. This barrier level will be too high to cross at lower temperatures.
University/College: University of California
Type of paper: Thesis/Dissertation Chapter
Date: 21 December 2016
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