Metal-ion assisted catalysis of nucleophilic attack. Part II. The pathway of zinc–base co-operation in aldehyde hydration

Abstract

A path for acetaldehyde hydration in which zinc and acetate or pyridine act as co-operative catalysts is described. Comparison with pyridine-2-carboxyiate shows that the zinc ion and the base are not bound to each other when acting as co-catalysts. In the presence of chloride ions a different type of co-operative catalysis is seen. The rates observed in the zinc–pyridine and –acetate co-operative catalysis of the hydration are analysed in terms of the concentrations of complex species present in solution. The only effect of a base bound to the metal ion appears to be to block some of the metal's catalytic co-ordination sites.