Effects of anionic micelles on the intramolecular general base-catalyzed hydrolysis of phenyl and methyl salicylates

✍ Scribed by M.Niyaz Khan

• Book ID: 103997647
• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 814 KB
• Volume: 102
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/1381-1169(95)90044-6

✦ Synopsis

The effects of micelles of sodium dodecyl sulphate (SDS) on hydrolytic cleavage of phenyl salicylate (PS) have been studied at 30 and 37°C under [ NaOH] range 0.003-0.060 M. The total concentration of SDS, [SDS] =, was varied from 0.02 to 0.40 M. The observed pseudo first-order rate constants, kobsr reveal decrease with increase in [ SDS]r at a constant [ NaOH] and temperature. These observed data have been treated with pseudophase model of the micelle. The rate of hydrolysis of micellized PS turns out to be insignificant compared to the rate of hydrolysis of non-micellized PS under the entire [ NaOH] range of the study. This is rationalized in terms of a proposal that micellized anionic PS molecules exist in the specific micellar region where water concentration, [ H*O], is much lower than the [ HZ01 of aqueous pseudophase. The kinetic data have been used to obtain the micellar binding constants, K, for ionized and K2 for non-ionized PS and the respective values of K, and K2 are 3.0 M-' and 1887 M-' at 30°C and 3.1 M-r and 986 M-' at 37°C. The observed pseudo first-order rate constants, kobs, for hydrolysis of methyl salicylate, MS, remain unchanged with change in [ SDS]r from 0.0 to 0.4 M at 0.03 M NaOH and 37°C. These observations are concluded to be the consequence of the location of the micellized MS molecules at the junctural region of the Gouy-Chapman and Stem layers where [ HZ01 is similar to [ HZ01 of aqueous pseudophase.