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23
Feb
The Cannizzaro reaction utilizes a strong base and two aldehydes with no α-hydrogens: one is reduced to the corresponding 1° alcohol, while the other is oxidized to a carboxylic acid in a maximum yield of 50% each. Although a variety of mechanisms have been proposed, the generally accepted mechanism involves a hydride transfer. Hydroxide attacks the first aldehyde, forming a tetrahedral intermediate, which is deprotonated to make a dianion intermediate. The dianion yields a carboxylic salt when it facilitates the aldehydic hydrogen to leave as a hydride ion that attacks the second aldehyde (in a rate-determining step) to afford the alkoxide of a 1° alcohol. The alkoxide is protonated to form the alcohol, and an acid work-up converts the carboxylate to a carboxylic acid.
- Reagents:Strong Base, Acid Work-Up
- Reactant: Aldehyde with no α-hydrogens
- Product: 1° Alcohol, Carboxylic Acid
- Type of Reaction: Redox Disproportionation
Lab Tips
- Aldol reactions take place faster than the Cannizzaro reaction if α-hydrogens are present on the starting aldehyde. [1][1][1]
- Synthetically useful α-hydroxy esters can be obtained from glyoxals via an intramolecular Cannizzaro reaction with an appropriate Lewis acid. [2]
- Reaction rates can be enhanced with good yields under microwave irradiation. [3] Moreover, solvent-free conditions can also enhance reaction rates. [4]
2. Russell, A. E., Miller, S. P., Morken, J. P. Efficient Lewis acid catalyzed intramolecular Cannizzaro reaction. J. Org. Chem. 2000, 65, 8381-8383.
3. Sharifi, A. et al. Microwave irradiation techniques for the Cannizzaro reaction. Tetrahedron Letters 1999, 40(5), 1179-1180.
4. Yoshizawa, K., Toyota, S., Toda, F. Solvent-free Claisen and Cannizzaro reactions. Tetrahedron Letters 2001, 42, 7983-7985.
Mechanism
Top Citations
Original Paper
Related Reactions
- Tishchenko Reaction
