Definition
Amines are organic molecules containing nitrogen (N) atoms bonded to carbon or hydrogen atoms. They are formally derived from ammonia, in which hydrogen atoms have been replaced by carbon atoms.
- Primary amines: 1 carbon atom
- Secondary amines: 2 carbon atoms
- Tertiary amines: 3 carbon atoms
The functional group is called the amino group, for example, R-NH2.
Nomenclature
The trivial name of a simple aliphatic amine is obtained by arranging the residues with the suffix -amine alphabetically. Thus, for example:
- Ethylmethylamine
- Methylamine
- Dimethylamine
- Ethylamine
- Propylamine
- Cyclohexylamine
- Diethylmethylamine
- Ethylmethylpropylamine
For the official IUPAC nomenclature, the prefix amino is also used. A distinction can be made between aliphatic and aromatic amines. The simplest aromatic amine is aniline. It consists of a benzene ring with a single amino group. The nitrogen-containing heterocycles also belong to the amines.
Properties
- The H-bridges of amines are less strong than those of comparable alcohols because nitrogen is less electronegative than oxygen.
- Primary and secondary amines have lower boiling points than comparable alcohols. On the other hand, they are higher than those of comparable alkanes.
- Amines with a small molecular mass are usually soluble in water.
- Amines are often characterized by an unpleasant, irritating, fishy or acrid odor.
- Amines have basic properties.
Chemical reactions of amines
Amines are bases and react with acids in an acid-base reaction:
- R-NH2 (primary amine) + HCl (hydrochloric acid) R-NH3+ + Cl–
The resulting positively charged ion is the ammonium ion (alkylammonium ion in this case). The salts are called ammonium salts. Because of the lone pair, the nitrogen is a nucleophile suitable for nucleophilic substitution. With a carboxylic acid, an amide is formed. With a halide, an amine can be alkylated.
Amines in pharmaceuticals
In pharmaceutics, the amino group is one of the most important functional groups in active ingredients. Countless pharmacologically active substances are amines, such as the alkaloids. An important reason is that amines can be both hydrogen bond acceptors and donors. This plays a crucial role in drug binding in the binding site or active site of drug targets. By the way, tertiary amines are an exception, which are only acceptors and not donors. Another reason is that amines are present in important biomolecules such as amino acids, proteins, nucleic acids, neurotransmitters and hormones. Finally, amines are also indispensable for the synthesis of active substances.
Abuse
Amines are misused for the illicit synthesis of narcotics. For example, methylamine can be used for the synthesis of ecstasy (MDMA).