Aldimine

Aldimine is an imine derived from an aldehyde, containing the characteristic carbon–nitrogen double bond. Its general structure is R-CH=NR′, where R is a substituent on the aldehyde carbon and NR′ represents the amine-derived substituent attached to nitrogen. Aldimines are sometimes referred to as aldehyde imines or Schiff bases when formed from aldehydes and amines.

Formation and relation to Schiff bases: Aldimines form by condensation of an aldehyde (R-CHO) with an amine, with the loss of water. This reaction is often catalyzed by acid or dehydration conditions. When activated by an amine, the resulting product is a Schiff base; the term Schiff base is broader and encompasses imines formed from both aldehydes and ketones with various amines. Aldimines specifically originate from aldehydes, whereas ketimines (or imines derived from ketones) come from ketones (R-CO-R′).

Reactivity and applications: The C=N bond in aldimines is electrophilic at carbon, enabling nucleophilic additions and hydrolysis back to the corresponding aldehyde and amine under aqueous conditions. Aldimines can be reduced to amines (hydrogenation) and serve as key intermediates in reductive amination, a common method for converting carbonyl compounds into amines. They also participate in various condensation and cyclization reactions in organic synthesis. Infrared spectroscopy typically shows a C=N stretch in the region around 1640–1690 cm⁻¹.

Notes: The term aldimine emphasizes derivation from aldehydes, while ketimines are derived from ketones. Aldimines share conceptual space with Schiff bases, but the former specifically refer to aldehyde-derived imines.