A new mechanism for the Cannizzaro reaction

CHED 339

Colleen Faith Cassidy, ccassidy@carthage.edu and Timothy Eckert, teckert@carthage.edu. Department of Organic Chemistry, Carthage College, 2001 Alford Park Dr Box 212, Kenosha, WI 53140
The Cannizzaro reaction is a well-known oxidation-reduction reaction discovered 150 years ago. It involves two aldehyde molecules, one reduced to an alcohol and the second oxidized to a carboxylic acid. The currently accepted mechanism involves the intermolecular transfer of a hydride ion, which is a strongly basic, unlikely leaving group. Although the accepted mechanism is consistent with the existing evidence for the reaction, it is not consistent with normal organic chemistry, where intermolecular hydride transfer from a carbon is not well established. While studying this reaction, we used methoxide ion as a base in place of hydroxide ion. Products resulted that could not be produced by the accepted mechanism. Our new mechanism, involving a pericyclic reaction, is consistent with NMR and other experimental results, and does not involve the unfavorable intermolecular hydride transfer.