Лако-красочные материалы — производство

Textbooks in general organic chemistry will illustrate that there are many ways of synthesising azo compounds. However, almost without excep­tion, azo dyes and pigments are made on an industrial scale by the same

two-stage reaction sequence: diazotisation and azo coupling, as illus­trated in Scheme 3.2.

The first stage, diazotisation, involves the treatment of a primary aromatic amine, referred to as the diazo component, with sodium nitrite under conditions of controlled acidity and at relatively low temperatures to form a diazonium salt. In the second stage of the sequence, azo coupling, the relatively unstable diazonium salt thus formed is reacted with a coupling component, which may be a phenol, an aromatic amine or a ^-ketoacid derivative, to form the azo dye or pigment. The next two sections of this chapter deal separately with these two reactions, with emphasis on the practical conditions used for the reactions and on the reaction mechanisms. This sequence of reactions provides an interesting illustration for students of organic chemistry of the ways in which the selection of the optimum practical conditions for the reactions is heavily influenced by consideration of the reaction mechanisms which are oper­ating.