Aromatic diazonium salts
Diazonium ions decompose on warming into aryl cations and nitrogen. Diazonium ions are subject to one-electron reduction with the formation of an aryl radical and nitrogen. The diazotization of primary aromatic amines is normally carried out by adding an aqueous solution of sodium nitrite to a solution of the amine hydrochloride in an excess of hydrochloric acid which is cooled by an ice-bath. Aromatic fluorides are prepared by the Schiemann reaction. The synthetic applications of aromatic diazonium salts are conveniently divided into those in which nitrogen is eliminated and those in which it is retained. Most reactions employing diazonium salts may be conducted in solution and it is not normally necessary to isolate the solid salt. A number of procedures lead to the arylation of aromatic carbon by diazonium salts. The use of either the Gomberg reaction or the diazoacetate method for the formation of biphenyls is normally less satisfactory than the aroyl peroxide method.