Method of preparing arylacetic acid alkyl esters

In a process of producing an alkyl ester of a substituted or unsubstituted arylacetic acid wherein a corresponding substituted or unsubstituted benzyl halide is reacted with carbon monoxide and an alcohol having an alkoxy group the same as that of said ester, the improvement which comprises carrying out said reaction in a basic reaction medium at a temperature of about 10.degree.-100.degree. C, and a carbon monoxide pressure of about 0.1-25 atmospheres in the presence as catalyst of at least one cobalt salt of the group cobalt halide, cobalt acetate, cobalt-acetylacetonate, cobalt nitrate, cobalthydroxide-carbonate and Co.sub.2 (CO).sub.8, at least one metal or metal alloy of the group manganese, iron, nickel and alloys thereof, and at least one water soluble sulfur compound of the group sodium dithionate, sulfoxylates, and sodium sulfide-sodium thiosulfate.