Process for preparing carboxylic acids by carbonylation of ethers and thioethers

A process for preparing an aryl-substituted aliphatic carboxylic acid thereof having the formula:

• ##STR4## where R.sub.1 is hydrogen or alkyl, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same or different and are hydrogen, alkyl, cycloalkyl, alkyl-substituted cycloalkyl, aryl either substituted or unsubstituted, alkoxy, alkylthio, heteroaryl either substituted or unsubstituted, alkanoyl, aroyl either substituted or unsubstituted, heteroarylcarbonyl either substituted or unsubstituted, trifluoromethyl or halo and Ar is unsubstituted or substituted aryl which comprises treating a compound of the formula:
• ##STR5## where X is sulfur or oxygen and R is alkyl or aryl either substituted or unsubstituted;
• Ar, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are as previously defined and water with carbon monoxide at a pressure of at least about 1 atmosphere and a temperature from about 25.degree. C. to about 200.degree. C. in the presence of a catalyst that is a) palladium(O) or a compound of palladium where palladium has a valence of 1 or 2 or b) a mixture of palladium(O) or the compounds of palladium where palladium has a valence of 1 or 2 and the compounds of copper having a valence of 1 or 2 and (c) at least one acid stable ligand.