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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.
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 hexamine. Imine formation generally takes place fastest between pH 4 and 5 and is slow at very low or very high pH.
- Addition reactions with primary amines give stable imines
- but with an aryl group or certain stabilizing alkyl substituents on nitrogen, (the imine is then called a Schiff base) the imine is truly stable, see alkylimino-de-oxo-bisubstitution.
- A secondary amine lacks hydrogen and elimination of water is not possible. The hemiaminal intermediate is not stable and
- note that addition of carbonyl compounds to the salt of an amine yields the corresponding Mannich base
- imine formation is part of the Friedländer synthesis of quinolines.
Imine reactions
- an imine can be reduced to an amine
- an imine can be hydrolysed with water to the corresponding amine and carbonyl compound
- an imine reacts with an amine to an aminal, see for example the synthesis of cucurbituril.
- an imine reacts with dienes in the Aza Diels-Alder reaction to a tetrahydropyridine.
- an aromatic imine reacts with an enol ether to a quinoline in the Povarov reaction
- A tosylimine reacts with an α,β-unsaturated carbonyl compound to an allylic amine in the Aza-Baylis-Hillman reaction
- imines are intermediates in the alkylation of amines with formic acid in the Eschweiler-Clarke reaction
See also
References
- March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. ISBN 0-471-85472-7
"Imine"