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

Pseudo-first order rate constants (k(obs)) and product ratios are reported for competing hydrolyses and alcoholyses of the reactive dichlorotriazine d ye (2) in water containing small amounts (usually <0.05 M) of added alcohol s (methanol, propan-1-ol, and four polyols: alpha- or beta -methylglucopyra noside, mannitol or sorbitol) at pH 11.2. Additional data are reported in t he 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 contr ibutions from hydrolysis (k(DOH)) and alcoholysis (k(DOR)) shows that k(DOH ) increases in polyol-water mixtures for 2, but not for the monofluorotriaz ine (1), and k(DOH) also increases for 2 in aqueous trifluoroethanol. The r esults are consistent with alkoxide-catalysed hydrolysis for 2, but with an uncatalysed or weakly-catalysed hydrolysis for 1, and provide indirect sup port 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 mix tures, containing both sodium carbonate and tetraalkylammonium salts, show rate enhancements particularly when the amount of sodium carbonate is low.