In below reaction, it is an example of Cannizzaro’s Reaction
HCHO + HCHO ———–> CH3OH + HCOOH
- Aldehydes do not have α (Alpha) hydrogen
- Using con Alkali (50% NaOH/KOH)
- Molecule undergo self-oxidation as well reduction
- Known disproportionating reaction
α (Alpha) hydrogen
- The Carbon directly connected to the functional groups
called α (Alpha) Carbon
- 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
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 understand, if there is no α Hydrogen in any aldehyde. it means it will give Cannizzaro’s Reaction.
Types of Cannizzaro’s Reaction :-
- Internal Cannizzaro’s Reaction
There is only one molecule but there is two group of aldehyde which gives Alcohol and carboxylic acid.
- Cross Cannizzaro’s Reaction
In Cross Cannizzaro’s reaction, there is two type 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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