The catalytic effect of catiohic amino micelles on the hydrolysis of substituted phenyl esters |
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| Institution: | 1. Division of Human Environmental Sciences, School of Applied Science and Technology, The Hebrew University, Jerusalem 91120, Israel;2. Department of Pharmacology, The Hebrew University, Jerusalem 91120, Israel;3. Department of Pharmaceutical Chemistry, School of Pharmacy, The Hebrew University, Jerusalem 91120, Israel;1. Dipartimento di Scienze Farmaceutiche (DISFARM), Sezione di Chimica Generale e Organica “Alessandro Marchesini” Università degli Studi di Milano, via Venezian 21, 20133 Milano, Italy;2. Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy;1. College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211800, China;2. College of Materials Science and Engineering, Nanjing Tech University, Nanjing 211800, China;3. State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing 211800, China;1. College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211800, China;2. College of Materials Science and Engineering, Nanjing Tech University, Nanjing 211800, China;3. State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing 211800, China |
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| Abstract: | The catalytic effects of two aminocationic micelles on the hydrolysis of substituted phenyldecanoate esters and a positively charched benzoate ester (CPNBA) were determined. The micellaric catalysts were of the general structure CH3(CH2)3N(CH3)2(CH2)nNH2]Br where n=2 (micelle 1); n=3 (micelle 2). The kinetics followed the expression: kobs =ko+kcat x Ka/(Ka+H+)+koOHOH-]. From the comparison of the kc OH rates with specific base catalysis rates deduced from reactions in non catalytic micelles, it was concluded that the kc OH term, is compatible mainly with an aminolysis reaction catalyzed by hydorxide ion. The Hammett and Bronsted correlations (p=2.8; β=1.0), in addition to the very small deuterium isotope effect, suggested that kcat corresponded with a nucleophilic mechanism. The Bronsted plot of log kcat vs pKa of the phenolate leaving groups in micelles 1 and 2 showed a biphasic behaviour. The break in the curve occured at pKo=5.89 and pKo=6.78 respectively. The partition ratio k±/k-a of the zwiterionic tetrahedral intermediate was derived from the experimental data and produced the following correlation: log k±/k-a=-0.92pKo+0.43pKN+2.466. The ester CPNBA exhibited a deuterium isotope effect of 2.1. From product analysis it was concluded that the reaction proceeds via a general base catalysis of aminolysis. |
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