Kinetics and mechanism of intramolecular general base-catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles

✍ Scribed by M. Niyaz Khan

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 934 KB
• Volume: 23
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550230910

✦ Synopsis

The alkanolysis of ionized phenyl salicylate, PS-, has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH2CHzOH and CH30H) contents of 15-74 or 92%, v/. The alkanolysis of PSinvolves intramolecular general base catalysis. At a constant concentration of SDS, [SDSh, the observed pseudo first-order rate constants, kobs, for the reactions of RQH with PSobtained at different concentration of ROH, [ ~H ] T , obey the relationship:

where k is the apparent second-order rate constant and KA is the association constant for dimerization of ROH molecules. Both k and KA decrease with increase in [SDS]T. At a constant [ ~H ] T , the rate constants, kob, show a decrease of nearly 2-fold with increase in [SDS]T from 0.0-0.3M. These results are explained in terms of pseudo-phase model of micelle. The rate constants for alkanolysis of PSin micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous-alkanol pseudophase. This is attributed largely to considerably low value of [RQH] in the specific micellar environment where micellar bound PS-molecules exist. The increase in [ROH]T decrease the value of the binding constant of PSwith SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PSare explained in terms of the porous cluster micellar structure.