Change in the Acid Hydrolysis Mechanism of Esters Enforced by Strongly Acid Microemulsions

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• 作者：E. Ferná ; ndez ; L. Garc&iacute ; a-R&iacute ; o ; P. Rodr&iacute ; guez-Dafonte
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：October 4, 2007
• 年：2007
• 卷：111
• 期：39
• 页码：11437 - 11442
• 全文大小：90K
• 年卷期：v.111,no.39(October 4, 2007)
• ISSN：1520-5207

文摘

A kinetic study was carried out on the acid hydrolysis of 4-nitrophenylacetate and 4-nitrophenyllaurate inwater/HOT/isooctane microemulsions. The substitution of Na⁺ in the sodium salt of bis(2-ethylhexyl)sulfosuccinate by H⁺ has permitted us to obtain a functionalized surfactant (HOT) and, consequently, stronglyacid microemulsions. The use of HOT-based microemulsions allows us to reach concentrations of H⁺ in theaqueous core corresponding to a Hammett acidity function of H₀ = -2. The rate constant at the interface andthe distribution constants of the carboxylic esters throughout the different microenvironments of themicroemulsion have been quantified by application of the pseudophase formalism. The results obtained showthat the hydrolysis rate constant at the interface increases as the water content of the system decreases. Thecorrelation of the rate constants at the interface of the microemulsion with the Hammett acidity function, H₀(on the basis of the Bunnett-Olsen criterion), has allowed us to confirm that the hydrolysis process takesplace via an A2 mechanism for high water contents and through an A1 mechanism for values of W 15 (W= [H₂O]/[HOT]).