Crossed Cannizzaro Reaction
The Crossed Cannizzaro Reaction is a special type of Cannizzaro reaction in which formaldehyde reacts with another aldehyde that contains α-hydrogen atoms. Instead of undergoing a normal Cannizzaro reaction, the aldehyde first forms an aldol-type intermediate and then participates in a redox reaction with formaldehyde.
Key Features
- This reaction is mainly useful when an aldehyde contains one or more α-hydrogens, because such aldehydes normally do not undergo the simple Cannizzaro reaction.
- In the presence of a strong base, the aldehyde first undergoes aldol condensation with formaldehyde.
- During this process, the α-hydrogens of the aldehyde are replaced with hydroxymethyl (–CH2OH) groups.
- The product formed is a β-hydroxy aldehyde, which then reacts with another molecule of formaldehyde to undergo the crossed Cannizzaro reaction.
Stepwise Summary
- Aldehyde with α-hydrogens reacts with formaldehyde.
- Hydroxymethyl group replaces the α-hydrogen(s).
- β-Hydroxy aldehyde intermediate is formed.
- This intermediate undergoes a Cannizzaro-type reaction with formaldehyde.
Industrial Importance
One of the major products formed through this reaction sequence is Pentaerythritol, a commercially important chemical.
- Pentaerythritol forms resins when esterified with polybasic acids — these resins are widely used in surface coatings.
- Its nitrated derivative, PETN (Pentaerythritol tetranitrate), is used as an explosive.
Thus, the crossed Cannizzaro reaction has both theoretical and industrial significance.
Detailed Notes:
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