trioxide or sources thereof: R2NH + SO3 -> R2NSO3H Acid-base reactions Alkyl amines protonate near pH=7 to give alkylammonium derivative. Diazotization Amines reacts with nitrous acid to give diazonium salts. The alkyl diazonium salts are of little importance because they are too unstable. The most important members are derivatives of aromatic amines such as aniline ("phenylamine") (A = aryl or naphthyl): ANH2 + HNO2 + HX -> AN2+ + X- + 2 H2O Anilines and naphthylamines form more stable diazonium salts, which can be isolated in the crystalline form. Diazonium salts undergo a variety of useful transformations involving replacement of the group with anions. For example, cuprous cyanide gives the corresponding nitriles: AN2+ + Y- -> AY + N2 Aryldiazonium couple with electron-rich aromatic compounds such as a phenol to form azo compounds. Such reactions are widely applied to the production of dyes. Conversion to imines Imine formation is an important reaction. Primary amines react with ketones and aldehydes to form imines. In the case of formaldehyde (R' H), these products typically exist as cyclic trimers. RNH2 + R'_2C=O -> R'_2C=NR + H2O Reduction of these imines gives secondary amines: R'_2C=NR + H2 -> R'_2CH-NHR Similarly, secondary amines react with ketones and aldehydes to form enamines: R2NH + R'(R''CH2)C=O -> R''CH=C(NR2)R' + H2O Overview An overview of the reactions of amines is given below: Biological activity Amines are ubiquitous in biology. The breakdown of amino acids releases amines, famously in the case of decaying fish which smell of trimethylamine. Many neurotransmitters are amines, including epinephrine, norepinephrine, dopamine, serotonin, and histamine. Protonated amino groups () are the most common positively charged moieties in proteins, specifically in the amino acid lysine. The anionic polymer DNA is typically bound to various amine-rich proteins. Additionally, the terminal charged primary ammonium on lysine forms salt bridges with carboxylate groups of other amino acids in polypeptides, which is one of the primary influences on the three-dimensional structures of proteins. Application of amines Dyes Primary aromatic amines are used as a starting material for the manufacture of azo dyes. It reacts with nitrous acid to form diazonium salt, which can undergo coupling reaction to form an azo compound. As azo-compounds are highly coloured, they are widely used in dyeing industries, such as: Methyl orange Direct brown 138 Sunset yellow FCF Ponceau Drugs Approximately 42% of drugs and drug candidates contain amine functional groups: Chlorpheniramine is an antihistamine