Amine A member of a group of organic compounds which can be considered as derived from ammonia by replacement of one or more hydrogens by organic radicals. Generally amines are bases of widely varying strengths, but a few which are actually acidic are known.
Amines constitute one of the most important classes of organic compounds. The lone pair of electrons on the amine nitrogen enables amines to participate in a large variety of reactions as a base or a nucleophile. Amines play prominent roles in biochemical systems; they are widely distributed in nature in the form of amino acids, alkaloids, and vitamins. Many complex amines have pronounced physiological activity, for example, epinephrine (adrenalin), thiamin or vitamin B1, and Novocaine. The odor of decaying fish is due to simple amines produced by bacterial action. Amines are used to manufacture many medicinal chemicals, such as sulfa drugs and anesthetics. The important synthetic fiber nylon is an amine derivative.
Amines are classified according to the number of hydrogens of ammonia which are replaced by radicals. Replacement of one hydrogen results in a primary amine (RNH₂), replacement of two hydrogens results in a secondary amine (R₂NH), and replacement of all three hydrogens results in a tertiary amine (R₃N). The substituent groups (R) may be alkyl, aryl, or aralkyl. Another group of amines are those in which the nitrogen forms part of a ring (heterocyclic amines). Examples of such compounds are nicotine, which is obtained commercially from tobacco for use as an insecticide, and serotonin, which plays a key role as a chemical mediator in the central nervous system.
Many aromatic and heterocyclic amines are known by trivial names, and derivatives are named as substitution products of the parent amine. Thus, C₆H₅NH₂, is aniline and C₆H₅NHC₂H₅ is N-ethylaniline.
According to the Bronsted-Lowry theory of acids and bases, amines are basic because they accept protons from acids. Stable salts suitable for the identification of amines are in general formed only with strong acids, such as hydrochloric, sulfuric, oxalic, chloroplatinic, or picric.
Commercial preparation of aliphatic amines can be accomplished by direct alkylation of ammonia or by catalytic alkylation of amines with alcohols at elevated temperatures. Reduction of various nitrogen functions carrying the nitrogen in a higher state of oxidation also leads to amines. Such functions are nitro, oximino, nitroso, and cyano. For the preparation of pure primary amines, Gabriel’s synthesis and Hofman n’s hypo halite reaction are preferred methods. The Bucherer reaction is satisfactory for the preparation of polynuclear primary aromatic amines.