Alkoxide-catalysed hydrolyses of a chlorotriazine in alcohol–water mixtures. A new indirect probe for hydroxide-catalysed hydrolysis

Abstract

Pseudo-first order rate constants (k_obs) and product ratios are reported for competing hydrolyses and alcoholyses of the reactive dichlorotriazine dye (2) in water containing small amounts (usually <0.05 M) of added alcohols (methanol, propan-1-ol, and four polyols: α- or β-methylglucopyranoside, mannitol or sorbitol) at pH 11.2. Additional data are reported in the presence of ethane-1,2-diol, prop-2-yn-1-ol and 2,2,2-trifluoroethanol. Dissection of k_obs for solvolysis of the dye (DX) into the separate contributions from hydrolysis (k_DOH) and alcoholysis (k_DOR) shows that k_DOH increases in polyol–water mixtures for 2, but not for the monofluorotriazine (1), and k_DOH also increases for 2 in aqueous trifluoroethanol. The results are consistent with alkoxide-catalysed hydrolysis for 2, but with an uncatalysed or weakly-catalysed hydrolysis for 1, and provide indirect support for the possibility of a third order process in which hydroxide could act as a base catalyst. Additional kinetic data for 2 in methanol–water mixtures, containing both sodium carbonate and tetraalkylammonium salts, show rate enhancements particularly when the amount of sodium carbonate is low.