MICELLAR CATALYZED HYDROLYSIS OF A PHOSPHATE ESTER IN AQUEOUS SOLUTIONS CONTAINING DIMETHYL SULFOXIDE
Abstract:
<p align="justify"> The hydrolysis of p-nitrophenyldiphenyl phosphate lil:ls studied in aqueous solutions containing micelles of diethylheptadeaylimidazolinium ethyl sulfate (DEHIES), sodium hydroxide .and various aonaentrations of dimethyl sulfoxide (DMSO). Pseudo-first order (k<sub>ψ</sub>) and second-order rate constants (k<sub>2</sub>) were determined at l5º, 25º, and 35 ºC and activation parameters such as Ea,ΔG<sup>≠</sup>, ΔH<sup>≠</sup> and ΔS<sup>≠</sup> were also measured. The rate profiles obtained for solutions containing 10-50% DMSO by volume exhibited clear maxima that shifted to higher concentrations of DEHIES as a function of DMSO added. For solutions containing 60-80% DMSO, there was no maximum in the rate profile, and inhibition of the reaction took place. Solutions containing 90% by volume of DMSO exhibited much higher reaction rates and considerably more catalysis. The experimental results are explained in terms of the Hughes-Ingold Theory, specific solvent effects, polarity, and internal pressure of the reaction medium. The interpretation and discussion of the results takes into consideration the formation of the stoichiometric hydrate DMSO.2H<sub>2</sub>O and the inhibitory effect of dimethyl sulfoxide on the formation of micelles of DEHIES. </p>
<p align="justify"> The hydrolysis of p-nitrophenyldiphenyl phosphate lil:ls studied in aqueous solutions containing micelles of diethylheptadeaylimidazolinium ethyl sulfate (DEHIES), sodium hydroxide .and various aonaentrations of dimethyl sulfoxide (DMSO). Pseudo-first order (k<sub>ψ</sub>) and second-order rate constants (k<sub>2</sub>) were determined at l5º, 25º, and 35 ºC and activation parameters such as Ea,ΔG<sup>≠</sup>, ΔH<sup>≠</sup> and ΔS<sup>≠</sup> were also measured. The rate profiles obtained for solutions containing 10-50% DMSO by volume exhibited clear maxima that shifted to higher concentrations of DEHIES as a function of DMSO added. For solutions containing 60-80% DMSO, there was no maximum in the rate profile, and inhibition of the reaction took place. Solutions containing 90% by volume of DMSO exhibited much higher reaction rates and considerably more catalysis. The experimental results are explained in terms of the Hughes-Ingold Theory, specific solvent effects, polarity, and internal pressure of the reaction medium. The interpretation and discussion of the results takes into consideration the formation of the stoichiometric hydrate DMSO.2H<sub>2</sub>O and the inhibitory effect of dimethyl sulfoxide on the formation of micelles of DEHIES. </p>
DOI: 10.48141/SBJCHEM.v1.n1.1993.79_1993.pdf
Download PDF