The azo coupling reactions of six five-membered ring heteroaromatic diazonium ions with 2- naphthol-3, 6-disulfonic acid are investigated kinetically at various pH values. The dependence of the measured rate constants on the acidity of the aqueous reaction system is evaluated. It can be shown that the 2-naphtholate-3, 6-disulfonate trianion reacts 4× 108-8× 108 times faster than the 2-naphthol-3, 6-disulfonate dianion. The rate constants of the six ...