Imine

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.

[edit] 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
- with no alpha hydrogen present it proceeds to form an 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
imine formation is part of the Friedländer synthesis of quinolines.

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.
A rearrangement in carbohydrate chemistry involving an imine is the Amadori rearrangement.