A Schiff base (or azomethine), named after Hugo Schiff, is a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group—but not hydrogen.^[1] Schiff bases are of the general formula R₁R₂C=N-R₃, where R₃ is an aryl or alkyl group that makes the Schiff base a stable imine. A Schiff base derived from an aniline, where R₃ is a phenyl or substituted phenyl, can be called an anil.^[2]

Schiff bases can be synthesized from an aromatic amine and a carbonyl compound by nucleophilic addition forming a hemiaminal, followed by a dehydration to generate an imine. In a typical reaction, 4,4'-diaminodiphenyl ether reacts with o-vanillin:^[3]

A mixture of 4,4'-diaminodiphenyl ether 1 (1.00 g, 5.00 mmol) and o-vanillin 2 (1.52 g , 10.00 mmol) in methanol (40.00 mL) is stirred at room temperature for one hour to give an orange precipitate and after filtration and washing with methanol to give the pure Schiff base 3 (2.27 g, 97.00%)

There is a Schiff base intermediate in the fructose 1,6-bisphosphate aldolase catalyzed reaction during glycolysis.

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