imines

Imines are organic compounds that feature a carbon–nitrogen double bond (C=N). In these molecules, the carbon is typically bonded to two substituents, while the nitrogen bears a hydrogen or substituent. A general representation is R2C=NR', and related forms include R-CH=NR' for aldimines and R2C=NR' for ketimines. The C=N bond is planar and the atoms are typically sp2-hybridized.

Aldimines and ketimines are distinguished by the carbonyl precursor from which they are derived. Aldimines arise from aldehydes reacting with primary amines, while ketimines come from ketones with primary amines. When the imine is formed from a primary amine and a carbonyl compound, the product is commonly called a Schiff base; secondary amines give enamines rather than imines.

Preparation of imines usually involves condensation reactions in which a carbonyl compound and an amine are dewatered, often in the presence of acid catalysts or dehydrating agents. Although the reaction is reversible, it can be driven to completion by removing water or using driving forces such as azeotropic distillation.

Reactivity of imines centers on the polarized C=N bond. The imine carbon is electrophilic and can undergo nucleophilic attack; imines can be hydrolyzed under aqueous or acidic conditions to yield a carbonyl compound and an amine. Reduction of imines, for example by catalytic hydrogenation, converts them into amines. In acidic media, imines can form iminium ions, which are key intermediates in various reaction processes.

Applications of imines include their use as intermediates in organic synthesis, the formation of Schiff base ligands for metal catalysts, and roles in dyes, polymers, and selective transformations.