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

✍ Scribed by M. Niyaz Khan

• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: English
• Weight: 507 KB
• Volume: 20
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550200604

✦ Synopsis

The first-order rate constants, kl, for 1,2-ethanediolysis (within the content of 1,2ethanediol of 5% to 908, u / u ) and 2-ethoxyethanolysis (within the 2-ethoxyethanol content of 5%to 60%, u / u ) of phenyl salicylate, PSH, in alkaline aqueous mixed solvents, fit to a relationship:

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 [ROHIT is the total concentration of ROH. Similar relationship between k , and [ROH], 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,-LROH], profile reveals the change in the solvent structure of the reaction medium at >60% i u / u ) of ROH content. It is proposed that alkanols exist in polymeric form, (ROH), , and the alkanolysis of PS ~ involves the pre-equilibrium formation of monomeric ROH from (ROH), , followed by an intramolecular general base-catalyzed nucleophilic attack at carbonyl carbon of ester. A slight negative KC1 salt-and slight positive n-Bu,NI salt-effect are obtained for 1,2-ethanediolysis while a significant positive n-Bu,NI salteffect is obtained for 2-ethoxyethanolysis of PS-.