The rate of hydrolysis of some dichlorotriazinyl reactive azo dyes is measured where the triazinyl-ring is attached to a derivative of H-acid in the buffer solutions over the range 25-35°C. The rate constants obtained at constant pH are pseudo-first-order, but they are dependent on the concentration of hydroxyl ion. This dependence of the hydrolysis constants on the hydroxyl ion concentration is explained, supposing that, as the pH of the dye solution increases, ionization of the phenolic hydroxyl group at the 8-positioh in the naphthalene ring occurs to give a less reactive ionized form.
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