Title: Intramolecular General Base Catalyzed Ester Hydrolysis. The Hydrolysis of 2-Aminobenzoate Esters
Abstract: Rate constants have been obtained for the hydrolysis of the trifluoroethyl, phenyl, and p-nitrophenyl esters of 2-aminobenzoic acid at 50 °C in H2O. The pseudo-first-order rate constants, kobsd, are pH independent from pH 8 to pH 4 (the pKa of the amine group conjugate acid). The 2-aminobenzoate esters hydrolyze with similar rate constants in the pH-independent reactions, and these water reactions are ∼2-fold slower in D2O than in H2O. The most likely mechanism involves intramolecular general base catalysis by the neighboring amine group. The rate enhancements in the pH-independent reaction in comparison with the pH-independent hydrolysis of the corresponding para substituted esters or the benzoate esters are 50−100-fold. In comparison with the hydroxide ion catalyzed reaction, the enhancement in kobsd at pH 4 with the phenyl ester is 105-fold. Intramolecular general base catalyzed reactions are assessed in respect to their relative advantages and disadvantages in enzyme catalysis. A general base catalyzed reaction can be more rapid at low pH than a nucleophilic reaction that has a marked dependence on pH and the leaving group.
Publication Year: 2002
Publication Date: 2002-04-17
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 33
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