anilines

Anilines are a class of aromatic amines in which an amino group (-NH2) is attached to an aromatic ring, usually benzene. The simplest member is aniline (phenylamine), with formula C6H5NH2. Anilines are typically colorless to pale yellow liquids or solids at room temperature and possess a strong, fishy odor. They are weak bases and form salts with acids, such as anilinium chloride. Substituted anilines—where other groups replace hydrogens on the ring—are widely studied and commercially important.

Production and reactions: The principal industrial route is catalytic hydrogenation of nitrobenzene to aniline using hydrogen and a metal catalyst (e.g., nickel) under pressure. In the laboratory, anilines can be prepared by reduction of nitrobenzenes with iron, tin, or catalytic systems. Anilines readily undergo electrophilic substitution and can couple with acylating agents to give anilides; they are precursors to dyes and polymers.

Applications and safety: A major class of aniline derivatives is used to produce the vast family of aniline dyes; aniline is also a key feedstock for manufacturing methylene diphenyl diisocyanate (MDI), a precursor to polyurethanes. Substituted anilines are used in pharmaceuticals and agrochemicals. Health and environmental concerns: aniline is toxic and can cause methemoglobinemia upon exposure; it should be handled with appropriate controls to limit skin absorption and inhalation, and it should be stored away from oxidizers and sources of ignition.