Abstract
Whereas the coupling reaction of 1-naphthol with p-substituted benzenediazonium salts occurs mainly at the 4-position of 1-naphthol, 1-diazonio-2-naphthol-4-sulfonate reacts with 1-naphthol preferentially at the 2-position, giving 2-azo dyestuff which is particularly important as acid mordant dyes. In order to disclose the mechanism for the regioselectivity of the coupling reaction, kinetic studies have been carried out at 25°C under constant ionic strength (0.5). The coupling takes place exclusively at 2-position of 1-naphthol to give 2-azo dyestuff. Logarithm of the apparent second order rate constant correlates linearly to the pH value with the gradient of O.5 at pH<10.1, and O5. at pH>10.1. The active species are concluded to be 1-naphtholate ion [Nap-] and 1-diazonio-4-sulfonato-2-naphthola. te ion [DSN-]. Acid catalysis by free 1-naphthol [NapH] is also found operative. The reaction rate, ν, is expressed as follorwes, Where kNaPH, ko denote the catalytic constant of [NapH] and the solvent constant, respectively.
