Carbonyl condensation
Organic reaction of carbonyl compounds with amines to imines
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Through Organic chemistry, Organic reaction and Carbonyl group
Reaction mechanism
The reaction steps are reversible reactions and the reaction is driven to completion by removal of water e.g. by azeotropic distillation, molecular sieves or titanium tetrachloride. Primary amines react through an unstable hemiaminal intermediate which then splits off water.
Secondary amines do not lose water easily because they do not have a proton available and instead they often react further to an aminal:
or when an α-carbonyl proton is present to an enamine:
In acidic environment the reaction product is an iminium salt by loss of water.
This reaction type is found in many Heterocycle preparations for example the Povarov reaction and the Friedländer-synthesis to quinolines.
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Intramolecular substitution
Compounds containing both a primary or secondary amine and carbonyl functional group are often labile. This guideline applies to amino aldehydes, amino-ketones, and amino-esters; indeed a molecule cannot carry simultaneously (unprotected) aldehyde and amine groups. Aminoacetone, the simplest amino ketone, cannot be isolated as a liquid or solid, and 2-aminobenzaldehyde oligomerizes in solution or in the melt. An α-formyl aziridine, reduced with DIBAL from the ester, reversibly dimerizes to an oxazolidine:
Related reactions
Hydrazines and hydroxylamines displace carbonyl oxygens much more readily than amines. Their equilibria strongly favor the dehydrated product, and the carbonyl is recovered only with difficulty.