Carbonylation of Alcohols and Esters

1 Carbonylation of Alcohols and Esters. The mechanism of ttie Rh/I catalysed alcohol carbonylation has been studied in detail. Rates decrease sharply from methanol to n-propanol. Formation of isobutyric acid as a by-product points to a p-H elimination-reinsertion sequence.This sequence has also been demonstrated for ethanol carbonylation by selective C labelling (eqn.l8). The reductive carbonylation of methanol in the presence of Col2 and PPhg generates acetaldehyde, ethanol and methyl acetate. Only diphenylether and alkanes as solvents did not decompose under the reaction conditions (17CPC, 

5000 psi). The carbonylation of methanol to methyl formate is catalysed by W(C0)g/0Me or [W2(C0) iqH] COj inhibits the reaction. The cobalt carbonyl catalysed-desulfurization of benzyl thiols gives COS and hydrocarbons CO insertion does not take place.Synthesis gas reacts with ethyl orthoformate under Ru/I catalysis to a mixture of hydrogenolysis and carbonylation products.A similar catalyst under more severe conditions converts methyl formate into acetic acid and methylacetate CO2 and methane are by-products The effectiveness of iodide promoters in the Ru catalysed carbonylation of methyl acetate decreases in the order PPh , KI Nal Li I Csl due to ion-pairing effects with the active species. The crystal structure of [K(18-crown-5)]+[fac-Ru(CO)3l3]- reveals weak interactions between K and the iodide ligands.Mixed Pd/Rh/MeI/PBui3 catalysts convert methyl acetate mainly to ethylidene diacetate (eqn.l9).  

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