Part A: Microscale Reduction of Benzil Weigh out 200 mg of benzil and add it to
ID: 538267 • Letter: P
Question
Part A: Microscale Reduction of Benzil Weigh out 200 mg of benzil and add it to a 10-mL Erlenmeyer flask. Add ethanol. Swirl to mix. Add 75 mg of sodium borohydride to the solution of benzil stand 10 minutes with occasional swirling. The yellow color will disappear as benz eyer flask. Add 2 mL of 95% zil. Let nzil is The solution should be clear and colorless. If necessary, filter off any insoluble impuri rlenmeyer reduced. Add 2 mL of water slowly as foaming may occur. Heat the solution to boilin ing e impun- ties, using a Pasteur filter pipet. Transfer the hot clear solution to a clean Erlenmever flask using a filter pipet. Add an additional 2 mL of hot water. Allow the solution to crystallize undisturbed to form shiny thin plates. Cool in an ice bath and then vacum filter the crystals, using a Hirsch funnel. Wash the crystals with a minimum amountof cold water. Weigh the product.Explanation / Answer
Sodium borohydride is a good reducing agent. Although not as powerful as lithium aluminum hydride (LiAlH4), it is very effective for the reduction of aldehydes and ketones to alcohols. By itself, it will generally not reduce esters, carboxylic acids, or amides (although it will reduce acyl chlorides to alcohols). It is also used in the second step of the oxymercuration reaction to replace mercury (Hg) with H.
lithium aluminum hydride (LiAlH4) although less reactive. For our purposes, sodium borohydride is really useful for one thing: it will reduce aldehydes and ketones. In this sense it traverses one rung on the oxidation.