Catalysis of Ester and Amide Hydrolysis

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catalysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (Kroll, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with amines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl 

Cu++-catalysed hydrolysis and 5-4 for alkaline hydrolysis of lsO-labelled ester. Formation of the tetrahedral intermediate in the scheme of equation (31) is indicated by the observed 1 sO-exchange. However, interactions of the carbonyl oxygen and the metal ion 

The following relative second-order rate constants have been obtained for hydroxide ion-catalysed hydrolysis glycine ethyl ester, 1 protonated glycine ethyl ester, 41 and the cupric ion complex of glycine ethyl ester, T3 X 10s (Conley and Martin, 1965). The large effect of the cupric ion cannot be due entirely to electrostatic effects, but rather to catalysis by direct co-ordination with the ester function. 

Metal-ion catalysis in these systems could take place by coordination of the metal ion with the amino-group and either the 

Stable cobalt(III) ion complexes with which ligand exchange does not occur were prepared by the scheme of equation (32) (Alexander and Busch, 1966 Buckingham et al., 1967a, b, c), and were isolated and characterized. Large rate enhancements in hydrolysis are observed in comparison with the uncomplexed esters for attack of H2 O at pH 1-4, but it is of greatest interest that the reactions are markedly catalysed by general bases. It has been observed that 

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Metal-ion Catalysis of Ester and Amide Hydrolysi Carboxyl Group Catalysis Mechanistic Conclusions... 

Broxton, T.J., Nasser, A. Micellar catalysis of organic reactions. Part 37. A comparison of the catalysis of ester and amide hydrolysis by copper-containing micelles. Can. J. Chem. 1997, 75, 202-206. 

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