Reducing Benzil Using Sodium Borohydride

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John Simmers and Keena Dickey Reducing Benzil Using Sodium Borohydride Purpose: The Purpose of this lab this lab is to reduce benzil using sodium borohydride, and then identify the product that was produced by testing the products melting point, mixture melting point, thin layer chromatography and infrared spectroscopy. Theory: Reductions in organic chemistry results from the addition of hydrogen or lose of oxygen from an organic molecule. When NaBH4 is at room temperature it is only able to reduce aldehydes and ketones to form the corresponding alcohol. NaBH4 is a much easier reducing agent than LiAlH4 because it reacts very slowly with protic solvents at room temperature. However NaBH4 has its down falls and decomposes in the presence of acidic functional groups like carboxylic acids, which means that acid groups must be reduced with a base such as sodium hydroxide before NaBH4 will be able to reduce an aldehyde or ketone. The reaction of NaBH4 is produced by the addition of a hydride ion to an organic substrate, and since this reducing agent contains four hydride one equivalent of NaBH4 is able to reduce up to four molecules of a ketone with a single carbonyl group. The mechanism for this reaction involves an irreversible nucleophilic addition of a hydride ion to the carbonyl group of benzil. Once the addition of this hydride ion occurs the carbonyl oxygen becomes protonated producing a positive charge on the carbonyl oxygen, which then recants to form a carbonyl alcohol via electrophilic addition of a hydrogen atom to the carbonyl oxygen. Since the carbonyl group of the ketone is trigonal planar molecule in its geometry it is able to be attacked from either side of the molecule by the hydride ion. Thus the alcohols that are formed produce a racemic mixture, which contains two enantiomers. The possible products which are formed from the reduction
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