Amine

An amine is an organic compound derived from ammonia (NH3) by replacing one or more hydrogen atoms with alkyl or aryl groups. The general structural motif is R3N for tertiary amines, with primary (RNH2) and secondary (R2NH) amines having one or two hydrogens on nitrogen, respectively. When four organic groups surround nitrogen, forming a positively charged ammonium center, the compound is a quaternary ammonium salt (R4N+ X−).

Names and classification reflect the substituents on nitrogen. Primary amines have one carbon substituent attached to nitrogen, secondary amines have two, and tertiary amines have three. Quaternary ammonium salts possess no lone pair on nitrogen and carry a counterion (for example, chloride). Aromatic amines, such as aniline, are amines where the nitrogen is attached to an aromatic ring and often show different basicity from aliphatic amines.

Amines are typically basic and act as nucleophiles in chemical reactions. In water, they accept a proton to form ammonium ions (R3NH+), and the strength of this base varies: aliphatic amines are generally more basic than anilines. Common reactions include alkylation to form tertiary and quaternary ammonium salts, acylation to give amides, and condensation with carbonyl compounds to form imines or enamines. Reductive transformations can convert nitro groups to amines, and amines are key intermediates in the synthesis of pharmaceuticals, dyes, agrochemicals, and polymers.

Safety and handling vary with structure; some amines are toxic or irritant, and aromatic amines can be carcinogenic. Notable examples include aniline, dimethylamine, diethylamine, and trimethylamine.