Chemical Biology 3OA3, September 2009 Page 50 Condensation of Benzil with Urea to Form Dilantin Benzil and urea when heated together with base as catalyst condense to form dilantin. One step of the process involves a phenyl shift so that both phenyls end up on the same carbon atom. While 1,2 shifts occur readily in the case of carbocations, they are rare in the case of anions. The rearrangement is analogous to the benzilic acid rearrangement. It is not clear in this case why the rearrangement occurs. Perhaps it is the stability of the imide (-CO-NH-CO-) group that drives it. Procedures: Benzoin In a 50-mL Erlenmeyer flask equipped with a stirring bar prepare a solution of 1.04 g (0.003 mole) of thiamine hydrochloride in 3 mL of water. When all of the thiamine hydrochloride has been dissolved, add 8 mL of 95% ethanol, 3 mL of 10% sodium hydroxide (0.006 mole), and 3 mL (3.2 g, 0.03 mole) of benzaldehyde, with vigorous stirring during each addition. Continue
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