Synthesis of acetic acid from methanol alone by homogeneous metal complex catalyst. Part II . Mechanistic study on methyl acetate formation from methanol alone by [( η5-C 5H 5)(PPh 3) 2RuX] (X=Cl, SnF 3) complex catalyst

Abstract

Catalytic activity of [( η 5-C 5H 5) (PPh 3) 2RuX] (X=Cl ( 1), SnF 3 ( 2)) was investigated for the highly selective formation of methyl acetate with methanol used as the sole source. Complex 2 was found to be more catalytically active than the singlemetallic complex 1. For both complexes, the initial reaction rate was first order with respect to the catalyst concentration, and a saturation curve was obtained for dependence on the reactant concentration. Extra addition of Cl − ion considerably slowed the reaction with 1 taken as catalyst, and an almost linear relationship was obtained between the reciprocal of initial rate and the concentration of added Cl − ion. This fact indicates the presence of pre-equilibrium to form catalyst-reactant complex through the substitution of Cl − ligand. In the case of 2, extra addition of PPh 3 gave a similar effect on the rate, allowing the same type of kinetic analysis. The role of Sn(II) ligand is considered in line with the mechanism that satisfies the rate equations derived from these kinetic results.