When 2 moles of benzaldehyde are treated with sodium hydroxide, a reaction occurs in

Chapter 20, Problem 20.32

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When 2 moles of benzaldehyde are treated with sodium hydroxide, a reaction occurs in which 1 mole of benzaldehyde is oxidized (giving benzoic acid) while the other mole of benzaldehyde is reduced (giving benzyl alcohol): H O 1) NaOH 2) H3O+ OH O H H OH This reaction, called the Cannizzaro reaction, is believed to occur via the following mechanism: A hydroxide ion serves as a nucleophile to attack the carbonyl group of benzaldehyde. The resulting intermediate then functions as a hydride reducing agent by delivering a hydride ion to another molecule of benzaldehyde. In this way, one molecule is reduced while the other is oxidized. (a) Draw a mechanism for the Cannizzaro reaction, consistent with the description above. (b) What is the function of H3O+ in the second step? (c) Water alone is not sufficient to accomplish the function of the second step. Explain.