Process for making carboxylic acid halides

A process for making carboxylic acid halides by reacting an alkyl halide having 1 to 6 carbon atoms or aryl halide or benzyl chloride with carbon monoxide optionally containing up to 30 volume % hydrogen under practically anhydrous conditions at temperatures of 350.degree. to 575.degree. K. under pressures of 1 to 300 bars in the presence of a catalyst system containing at least one noble metal belonging to Group VIII of the Periodic System of the elements or its compounds, iodine and/or its compounds, optionally at least one compound selected from the non-noble metals Ce, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, As, Sb, Bi, Cr, Mo, W, Mn, Re, Fe, Co or Ni and optionally an inert organic solvent which comprises using a catalyst system essentially free of organic phosphorus compounds which additionally contains a compound of the elements belonging to groups I to III of the Periodic System and acetic acid, the amount of acetic acid included in the catalyst system being about 50-500 moles per mole of said noble metal or its compounds.