A Pd/C-HCl catalytic system is highly active and selective in the hydrogen transfer from H 2 O-CO to ArCHOHCOOH for the synthesis of ArCH 2 COOH (Ar is para substituted with a OH group). Typical reaction conditions are: temperature 50-70°C; P C O 20-80 atm; solvent: acetonitrile; substrate/Pd/HCl/H 2 O = 200-400/1/25-100/500-2000; [Pd] = 0.6-1.2 mmol l - 1 . The reaction rate is approximately of the first order with respect to ArCHOHCOOH. The yield increases with the increasing of P C O and of the temperature, as expected, and passes through a maximum with the increasing of the concentration of H 2 O and of HCl. The proposed catalytic cycle proceeds through the following steps. (i) H 2 O and CO interact with the metal giving rise to an intermediate having a Pd-COOH moiety, which, upon β-hydride abstraction, gives off CO 2 with formation of a Pd-H species. (ii) The starting substrate is in equilibrium, in the presence of HCl, with the corresponding chloride ArCHClCOOH, which adds to the metal forming an intermediate having a Pd-CH(Ar) COOH moiety. (iii) This species interacts with the hydride yielding the product ArCH 2 COOH and regenerating the catalyst. The reaction is compared to the closely related catalyzed water gas shift reaction.