Schiff base

 ( Functional Groups ) 

In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure. Anil refers to a common subset of Schiff bases: imines derived from . The term can be synonymous with azomethine which refers specifically to secondary aldimines (i.e. where R' ≠ H).

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Synthesis Schiff bases can be synthesized from an aliphatic amine or 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'-oxydianiline reacts with o-vanillin:

1 (1.00 g, 5.00 mmol) and o-vanillin 2 (1.52 g, 10.0 mmol) in methanol (40.0 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%)]]Schiff bases can also be synthesized via the Aza-Wittig reaction.

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Biochemistry Schiff bases have been investigated in relation to a wide range of contexts, including antimicrobial, antiviral and anticancer activity. They have also been considered for the inhibition of amyloid-β aggregation.

(2025). 9783110526912, de Gruyter GmbH. ISBN 9783110526912

Schiff bases are common enzymatic intermediates where an amine, such as the terminal group of a lysine residue, reversibly reacts with an aldehyde or ketone of a cofactor or substrate. The common enzyme cofactor pyridoxal phosphate (PLP) forms a Schiff base with a lysine residue and is transaldiminated to the substrate(s). Similarly, the cofactor retinal forms a Schiff base in , including human rhodopsin (via Lysine 296), which is key in the photoreception mechanism.

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Coordination chemistry The term Schiff base is normally applied to these compounds when they are being used as to form coordination complexes with metal ions. One example is Jacobsen's catalyst. The imine nitrogen is basic and exhibits Pi backbonding. Several, especially the are noninnocent ligands. Many Schiff base ligands are derived from alkyl and aromatic aldehydes.

(2025). 9780080437484 ISBN 9780080437484

Chiral Schiff bases were one of the first ligands used for asymmetric catalysis. In 1968 Ryōji Noyori developed a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene. Schiff bases have also been incorporated into metal–organic frameworks (MOF).

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Conjugated Schiff bases Conjugated Schiff bases absorb strongly in the UV-visible region of the electromagnetic spectrum. This absorption is the basis of the anisidine value, which is a measure of oxidative spoilage for fats and oils.

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Historic references

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