An imine is a functional group or chemical compound containing a carbon-nitrogen double bond. An imine can be synthesised by nucleophilic addition from a ketone or aldehyde and ammonia or an amine to a hemiaminal -C(OH)(NHR)- followed by elimination of water to the imine.

Synthesis

• The addition of ammonia to an aldehyde or ketone does not lead to a stable imine. The reaction of formaldehyde and ammonia yields hexamethylenetetramine .
• Addition reactions with primary amines give stable imines
• but with an aryl substituent on nitrogen, (the imine is then called a Schiff base) the imine is truly stable.
• A secondary amine lacks hydrogen and elimination of water is not possible. The hemiaminal intermediate is not stable and
  • with no alpha hydrogen present it proceeds to form a aminal
  • with alpha hydrogen present it proceeds to form an enamine
• note that addition of carbonyl compounds to the salt of an amine yields the corresponding Mannich base

Reactions

• an imine can be reduced to an amine
• an imine can be hydrolysed with water to the corresponding amine and carbonyl compound

References

• March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. ISBN 0-471-85472-7