The Carbonylation of Methanol Catalyzed by Rhodium Complexes in Solution

THE CARBONYLATION OF METHANOL CATALYZED BY RHODIUM COMPLEXES IN SOLUTION 

The only dependencies noted in the kinetic studies were first-order dependencies on iodide promoter and rhodium concentrations. Thus there was no observed effect of varying methanol concentration, and the partial pressure of carbon monoxide had no effect on the reaction rate. Similarly, the concentration of the products, methyl acetate and acetic acid, has no effect on the reaction rate. Thus we have the unusual situation of a reaction, CH3OH + CO — CH3COzH, in which the concentrations of the reactants and product have no kinetic influence. 

Quite different types of rhodium compound can give very similar reaction rates in a system which shows a kinetic dependence on the rhodium catalyst concentration. In particular, rhodium(III) halides and rho-dium(I) phosphine complexes give almost identical reaction rates after an initial induction period. Thus, in the case of these two systems, it appears that a common species is being formed. 

Spectroscopic investigations have shown that the carbonylation of rhodium(III) halides in alcoholic (9) and aqueous media (10) results in the formation of the dicarbonyldihalorhodate(I) anions, e.g., RhX3 + 3CO + HjjO - [Rh(CO)2X2]- + C02 + 2H+. 

two quite different forms of rhodium catalyst precursor can give the same rhodium species under the carbonylation reaction conditions. 

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