Synthesis and kinetic study of a series of chloro- and m-carboxypyridium triazinyl reactive dyes

Five monochloro-s-triazinyl reactive dyes (MCT) and five m-carboxypyridium-s-triazinyl reactive dyes (NTR) were synthesised with the same red chromophore bearing an –NHCN, –OCH₃, –CH₃NSO₂CH₃, –N-methyl phenyl or –OH group as ‘second-leg’ substituents. A kinetic study of the hydrolysis of these dyes was conducted, and the rate constant (k_obs) and half-life time values were determined. The k_obs of the MCT and NTR dyes was found to follow the order –OCH₃ > –CH₃NSO₂CH₃ > –N-methyl phenyl > –NHCN > –OH, which was approximately in agreement with the values obtained for the Hammett substituent constants. Overall, the higher the electron-donating property of the substituent on meta-position to the leaving group in the triazine ring, the lower the hydrolysis rate constant.