Transesterification of phenyl salicylate II . Kinetics and mechanism of intramolecular general base‐catalyzed cleavage of phenyl salicylate under the presence of 1,2‐ethanediol and 2‐ethoxyethanol

The first‐order rate constants, k 1 , for 1,2‐ethanediolysis (within the content of 1,2‐ethanediol of 5% to 90%, v / v ) and 2‐ethoxyethanolysis (within the 2‐ethoxyethanol content of 5% to 60%, v / v ) of phenyl salicylate, PSH, in alkaline aqueous mixed solvents, fit to a relationship: k 1 = k [ROH] T /(1 + K [ROH] T ) where k and K represent the secondorder rate constant for the reaction of alkanol, ROH, with ionized phenyl salicylate, PS − , and association constant for the dimerization of ROH, respectively, and [ROH] T is the total concentration of ROH. Similar relationship between k 1 and [ROH] T has been found for 1,2‐ethanediolysis of PS − studied in mixed solvents containing 1,2‐ethanediol and MeCN. In the alkaline aqueous mixed solvents containing 2‐ethoxyethanol, the k 1 ‐[ROH] T profile reveals the change in the solvent structure of the reaction medium at >60% ( v / v ) of ROH content. It is proposed that alkanols exist in polymeric form, (ROH) n , and the alkanolysis of PS − involves the pre‐equilibrium formation of monomeric ROH from (ROH) n , followed by an intramolecular general base‐catalyzed nucleophilic attack at carbonyl carbon of ester. A slight negative KCl salt‐ and slight positive n ‐Bu 4 NI salt‐effect are obtained for 1,2‐ethanediolysis while a significant positive n ‐Bu 4 NI salt‐effect is obtained for 2‐ethoxyethanolysis of PS − .