Cannizzaro reaction enolizable aldehydes

The Cannizzaro reactionof non-enolizable aldehydes is another example of a hydride transfer reaction. It is carried out under alkaline conditions and involves not only the addition of a hydroxide ion to one aldehyde but the stabilization of the resultant acid as the anion (Scheme 3.41). Methanal (formaldehyde), which gives methanoic acid (formic acid), a relatively strong carboxylic acid, makes a good hydrogen donor in a cross-Cannizzaro reaction. 

Various methods, many with an eye towards industrial application, have been examined to accelerate Cannizzaro reactions. For example copper-silica catalysts,Na2S, Na2S203 or NaaSOs supported on AI2O3, and ultrasound all have been reported to accelerate certain Cannizzaro processes. An extremely promising development is the use of transition metal catalysts, which may be employed under neutral conditions in the absence of strong base. This permits the use of enolizable aldehydes like (28), which under basic conditions would immediately be consumed via aldol reactions. For example, in the presence... 

Non-enolizable aldehydes and ketones may undergo the benzoin or Cannizzaro reactions. 

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