Glycine hydrolysis, metal catalysis

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 catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 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 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

Angelici and his collaborators [20] have studied the catalytic effect of a variety of metal ions on the base hydrolysis of ethyl glycinate N,N-diacetate (7.4), i.e. the monomethyl ester of nitrilotriacetic acid. Copper(II) catalysis is believed to involve... 

Co(II) and Cu(II) ions can promote the hydrolysis of glycine ethyl esters at pH 7 to 8, 25 C, conditions under which they are otherwise stable. Com-plexation takes place between the metal ion (M " ) and the amino acid ester to form a five-membered metal chelate. Subsequently, catalysis occurs as a result of the coordination of the metal ion with the amino and ester functions of the amino acid. In either case the metal ion can polarize the carbonyl group, thereby promoting attack of OH". The rate of hydrolysis increases with pH showing that OH" ion participates in the mechanism. Thermodynamically the hydrolysis occurs presumably because the carboxylate anion formed coordinates more strongly to the metal cation than the starting ester. 

Solvolysis of Organic Ligands.— The catalysis of hydrolysis of organic esters by metal ions or complexes has been much studied for many years. Recent examples of kinetic studies include hydrolysis of oxalate esters catalysed by a variety of ions, and of the bis[-L-(-J-)-histidine methyl ester] complexes of copper(n) and of nickel(n). The relative catalytic effects of several copper(n) complexes, including Cu(imda), Cu(nta), and Cu(dien) +, on the hydrolysis of methyl glycinate have been determined. Rate constants for base hydrolysis of this ester correlate with stability constants for mixed complexes of this ester with the above-named copper(n) complexes. ... 

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