Cannizzaro’s Reaction

In below reaction, it is an example of Cannizzaro’s Reaction

HCHO  +  HCHO  ———–>   CH3OH  +  HCOOH
50% NaOH

  1. Aldehydes do not have α (Alpha) hydrogen
  2. Using con Alkali (50% NaOH/KOH)
  3. Molecule undergo self-oxidation as well reduction
  4. Known disproportionating reaction

α (Alpha) hydrogen

  1. The Carbon directly connected to the functional groups

called α (Alpha) Carbon

  1. The Hydrogen associated with that carbon is called α Hydrogen

Let’s check with some chemical structures

Acetone | CH3COCH3

In Acetone, carbon group attached with Hydrogen through α Hydrogen

and carbon group attached with α Carbon

Acetaldehyde | C2H4O

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hydrogen and carbon connected though α Hydrogen with a main functional group. therefore in Acetaldehyde, there is one α carbon and three α hydrogen present.

Formaldehyde | CH2O

There is no α Hydrogen

Benzaldehyde | C7H6O

There is no α Hydrogen in benzaldehyde

Benzophenone | C13H10O

There is no α Hydrogen in Benzophenone but there are two α carbons

Cyclohexanone | C6H10O

cyclohexanone connected with two α carbons and four α hydrogen. so you can say α Hydrogen present in cyclohexanone.

Cyclohexanol | C6H12O

There is one α hydrogen and one α carbon present in cyclohexanol

now you must be understood, if there is no α Hydrogen in any aldehyde. it means it will give Cannizzaro’s Reaction.

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Types of Cannizzaro’s Reaction:-

  •  Internal Cannizzaro’s Reaction

There is only one molecule but there are two groups of aldehyde which give Alcohol and carboxylic acid.

  •  Cross Cannizzaro’s Reaction

In Cross Cannizzaro’s reaction, there are two types of Aldehyde. the small molecule will change carboxylic acid and another will change into alcohol.

Mechanism of Cannizzaro’s Reaction

Step 1:- Attach of a nucleophile on carbonyl carbon for from an anion

Step 2:- The anion act as a hydride donor to the 2nd molecule of aldehyde.

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