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Benzoin Reduction Mechanism

Submitted by bthoole on Sun, 11/04/2018 - 21:20

In this lab, benzoin was reduced by the addition of sodium borohydride. The product was identified as 1,2-diphenylethane-1,2-diol based on analysis of the reaction mechanism and comparative melting points taken from the literature. Sodium borohydride is a metal hydride that is capable of serving as a reducing agent. The reducing agent contains a metal hydrogen bond that is the source of a hydride ion. Sodium borohydride is a more selective reducing agent because of the polarity between the boron and hydrogen bond and as a result will only reduce aldehydes and ketones. The addition of sodium borohydride along with hydrochloric acid to the benzoin in ethanol provided the necessary components of the reaction to occur. The double bond to the oxygen in the benzoin was attacked by the sodium borohydride so that it became a single bonded negative oxygen which was then capable of reacting with the hydrogen provided by the addition of hydrochloric acid and water. The quenching allowed the negative oxygen to bond with hydrogen and become a hydroxyl group. The reduction reaction causes oxygen to lose bonds and, in this case, the double bond to oxygen in benzoin became a single bond to a hydroxyl group in hydrobenzoin. A crude product was generated as a first step and then recrystallized to purify the product. The purified product, along with the starting material and crude product were then analyzed with thin layer chromatography and melting points.

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