Abstract
Decarboxylation of oxalacetic acid (OAA) by metal chelates was examined, using copper (II) as a metal and seven kinds of ligand, which forms N, N-coordinated five membered ring chelate, used were 6, 6'-dimethyl-α, α'-dipyridyl, 4, 4'-dimethyl-α, α'-dipyridyl, α, α'-dipyridyl, 5-nitro-ο-phenanthroline, ο-phenanthroline, 4, 7-dimethyl-ο-phenanthroline, and ethylenediamine. When the concentration ratio of dipyridyl to copper (II) was varied, 1 : 1 ratio of copper to dipyridyl effected the fastest decarboxylation rate of OAA, and the rate was faster than that by copper (II) ion alone. Effect of each ligand on the reaction rate was examined and the reaction rate fell in the order of α, α'-dipyridyl, ο-phenanthroline, and ethylenediamine ; 5-nitro-ο-phenanthroline, ο-phenanthroline, and 4, 7-dimethyl-ο-phenanthroline ; α, α'-dipyridyl, 6, 6'-dimethyl-α, α'-dipyridyl, and 4, 4'-dimethyl-α, α'-dipyridyl. When the acetate buffer concentration was 0.1M, the reaction rate was faster, the smaller the pKa, and greater the catalytic effect. When the buffer concentration was 1.0M, the above order did not hold. It was also revealed that steric effect of the ligand affected this reaction. The intermediate formed in this decarboxylation reaction was examined by the measurement of ultraviolet and infrared spectra, and by isolation of this intermediate, and formation of a mixed chelate compound of OAA, copper, and ligand was confirmed.
