Activity of ruthenium/iodine catalysts for the carbonylation of esters to give carboxylic acids

Abstract

Abstract Homogeneous ruthenium/iodide systems under a pressure of carbon monoxide effectively catalyze the isomerization of methyl formate to acetic acid with yields in the range of 70%. If alkyl acetates are treated with CO/H 2 , the dominant process is the carbonylation of the alkoxy moiety rather than the homologation of the acetyl or alkoxy moieties; e.g. n-butyl acetate is converted mainly into valeric acid and its derivatives, along with acetic acid and butane. Only in the case of methyl acetate is homologation of the alkoxy moiety, to give ethyl acetate along with acetic acid, the major process. This duality of behaviour can be rationalized in terms of η 2 -acetyl intermediates, which can be hydrogenated to ethanol rather than hydrolyzed to acetic acid. Ester carbonylation is shown to be fast compared with alcohol carbonylation or acid homologation; esters are probably intermediates in the last process.