Amines

AMINES, organic derivatives of ammonia, i.e., ammonia in which one or several hydrogen atoms are replaced by hydrocarbon residues—alkyls (see) or aryls. Depending on the number of hydrogen atoms replaced in the ammonia, one distinguishes primary RNH₂, secondary R₂NH, and tertiary amines R₃N. Some amines have great biological significance and are found in nature, mainly as products of protein decomposition (see). Amines possess basic properties to a greater or lesser degree and form salts with acids, analogous to ammonium salts. The lower members of the amine fatty series are gases, usually with the odor of ammonia, from which they differ by their combustibility; the middle members are liquids; the higher members are solids. Synthetically, amines of the fatty series are obtained: 1. By the action of ammonia on alkyl halides. 2. By the Hofmann reaction, which consists of the action of chlorine or bromine in an alkaline solution on acid amides; this yields an amine with one less carbon atom than in the starting product. This method is also used for obtaining aromatic amines. 3. By the reduction of nitro, nitroso, and cyano compounds. Amines of the aromatic series, containing the amide group NH₂ in the nucleus, are liquids or solids that differ from fatty amines by less sharply defined basic (alkaline) properties and by their reaction with nitrous acid. While fatty primary amines decompose upon the action of nitrous acid into the corresponding alcohol, water, and N, aromatic amines yield diazo compounds (see Diazo-coupling). Aromatic amines are usually obtained by the reduction of easily accessible nitro compounds (see): R.NO₂+3H₂=R.NH₂+2H₂O. To detect amines, a number of reactions are used, of which the following are of the most significant importance. Upon heating primary amines with chloroform and a solution of caustic potash, isonitriles are formed, which possess an extremely unpleasant odor. Secondary amines, upon the action of nitrous acid, are converted into nitrosamines, which, when heated with phenol and concentrated sulfuric acid, after neutralization with caustic alkali, yield solutions colored a deep blue. All amines, with the exception of tertiary ones, react with acid anhydrides or acid chlorides, forming substituted acid amides, and with alkyl halides, replacing the hydrogen of the amide group with an alkyl; tertiary amines yield salts of ammonium bases with alkyl halides; these reactions are of great importance in pharmaceutical chemistry.