The Cannizzaro reaction is a redox reaction in which two molecules of an aldehyde are reacted to produce a primary alcohol and a carboxylic acid using a hydroxide base. The reaction begins with hydroxide attack on the carbonyl carbon followed by deprotonation to give a dianion. This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process the dianion converts to a carboxylate anion and the aldehyde to an alkoxide. The alkoxide then picks up a proton from water to provide the alcohol final product, while the caboxylate is converted to the carboxylic acid product after acid work-up.
Cannizzaro, S. Ann. Chem. Pharm. 1853, 88, 129–130.