S. Possidonio, O. A. Seoud
May 1, 1999
Citations
0
Influential Citations
12
Citations
Journal
Journal of Molecular Liquids
Abstract
Abstract The pH-independent hydrolysis of bis (2,4-dinitrophenyl) carbonate in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl group = cetyl and dodecyl), and polyoxyethylene (9) nonylphenyl ether has been studied spectrophotometrically. Observed rate constants, kobs, decrease in the following order: alkyldimethylbenzylammonium chlorides > bulk water ≈ alkyltrimethyl- ammonium chlorides > nonionic micelles > anionic micelles. Surfactant-substrate association constants have been determined from the dependence of kobs on [surfactant]. 1H NMR study of the solubilization of a model compound, phenyl-2,4-dinitrophenyl carbonate, showed that all surfactant segments are affected by the solubilizate, and that the ester penetrates deeper in micelles of alkyldimethylbenzylammonium chlorides relative to the corresponding alkyltrimethylammonium chlorides. Micellar effects on kobs are analyzed in terms of “medium” and “electrostatic” effects. The lower microscopic polarity at the reaction site cause rate decrease, whereas electrostatic interactions of the dipolar transition state with the charged interface result in rate decrease by anionic micelles, and rate enhancement by cationic ones.