The first-order rate constants, k , , obtained for methanolysis and ethanolysis of phenyl salicylate (PSH) in aqueous mixed solvents, fit to a relationship: k, = A , .
[ROHIT/(1 + A,[ROHIT) where A , and A, are the unknown parameters and [ROHIT is the total concentration of alkanol. It is proposed that the alkanolysis of PSH involves the preequilibrium formation of monomeric ROH from polymeric (ROH), , followed by an intramolecular general base-catalysed nucleophilic attack by monomeric ROH on the carbonyl carbon of the ester. In the mixed solvents containing alkanol and MeCN, the k i -[ROHIT profiles obtained in the presence of Kions are different from those obtained in the presence of Na ions which could be attributed to the cation-induced changes in the alkanol structure. Negative KCl salt effect has been observed on methanolysis of PSH, while it is essentially unaffected by the presence of tetraalkylammonium iodide salts (R,NI). The rates of ethanolysis of PSH have been found to increase with increase in [R,NI] and this increase becomes more pronounced with increasing hydrophobic surface area of R,NI. The rate constants for methanolysis of PSH in aqueous mixed solvents containing 80% MeOH (u/u) are independent of [OH] within the [OH] range of 0.01 to 0.15 M. The rate of methanolysis could not be detected within ca. 47 h in mixed solvents containing 96% HeOH (3.8% MeCN and 0.2% H20), 8 0 9 MeOH (19.8% MeCN and 0.2% H,O), and 0.022 M HCl. It is concluded that for efficient transesterification, PSH should exist in ionized form. The reaction of PSH with MeOH is ca. 400 times faster than that with t-BuOH which could be ascribed to the most likely steric effect. The values of AH* and A S * obtained for methancilysis and ethanolysis are essentially independent of [ROH] within the ROH content of 20% to 96% for MeOH and 50% to 96% for EtOH. The effect of organic co-solvent on rate of hydrolysis of PSH could be explained in terms of organic co-solvent-induced water polarization.