Aniline and Its Derivatives
Authors: Amini Bijan , Lowenkron Steven 
Published: July 2004

Aniline (benzenamine) is the simplest of the primary aromatic amines. Aromatic amines can be produced by reduction of the corresponding nitro compound, the ammonolysis of an aromatic halide or phenol, and by direct amination of the aromatic ring. At present, the catalytic reduction of nitrobenzene is the predominant process for manufacture of aniline. Pure, freshly distilled aniline is a colorless, oily liquid that darkens on exposure to light and air. It has a characteristic sweet, amine‐like aromatic odor. Aromatic amines are usually weaker bases than aliphatic amines. Aromatic amines form addition compounds and complexes with many inorganic substances, such as zinc chloride, copper chloride, uranium tetrachloride, or boron trifluoride. Various metals react with the amino group to form metal anilides; and hydrochloric, sulfuric, or phosphoric acid salts of aniline are important intermediates in the dye industry. Important reactions include
n
‐alkylation, ring alkylation, acylation, condensation, cyclization, reaction with nitrous acid, oxidation, halogenation, sulfonation, nitration, and reduction. The predominant process for manufacture of aniline is the catalytic reduction of nitrobenzene with hydrogen. The flash point of aniline (70°C) is well above its normal storage temperature, but aniline should be stored and used in areas with minimum fire hazard. Aniline is slightly corrosive to some metals. It attacks copper, brass, and other copper alloys, and use of these metals should be avoided in equipment that is used to handle aniline. Aniline is shipped in tank truck and tank car quantities and is classified by the U.S. Department of Transportation (DOT) as a Class B poison (UN 1547), and must carry a poison label. Wastes contaminated with aniline may be listed as RCRA Hazardous Waste. Aniline is highly toxic and may be fatal if swallowed, inhaled, or absorbed through the skin. Aniline vapor is mildly irritating to the eye, and in liquid form it can be a severe eye irritant and cause corneal damage. Based on tests with laboratory animals, aniline may cause cancer. Aniline should be handled in areas with adequate ventilation and skin exposure should be avoided by the wearing of proper safety equipment. The major uses of aniline are in the manufacture of polymers, rubber, agricultural chemicals, dyes and pigments, pharmaceuticals, and photographic chemicals. Most derivatives of aniline are prepared by hydrogenation of their nitroaromatic precursors.

An important derivative of aniline is 4,4′‐methylenedianiline (4,4′‐MDA). Manufacture is carried out by the acid‐catalyzed reaction of formaldehyde with aniline. All processes produce polymeric MDA (PMDA), which consists of mixtures of isomers and oligomers of MDA. More than 99% of the manufactured PMDA products are used in reactions with phosgene to produce the corresponding isocyanates for use in polyurethanes. The resultant polymeric isocyanates (PMDI) are either sold commercially or are purified to isolate 4‐4′‐methylenediphyenyldiisocyanate (MDI). MDI is an important intermediate in the manufacture of spandex fibers, thermoplastic resins, and coatings, and it is used in reaction injection molding (RIM) for automotive applications. The primary use of PMDI products is in rigid foam insulation, but they are also used in semiflexible foams, foundry core binders, and particle board manufacture.