SYNTHESIS OF ARYLACETIC ACID-DERIVATIVES FROM MANDELIC-ACID DERIVATIVES BY HYDROGEN-TRANSFER FROM H2O-CO CATALYZED BY A PD C-HCL SYSTEM/

A Pd/C-HCl catalytic system is highly active and selective in the hydr ogen transfer from H2O-CO to ArCHOHCOOH for the synthesis of ArCH2COOH (Ar is para substituted with a OH group). Typical reaction conditions are: temperature 50-70 degrees C; P-CO 20-80 atm; solvent: acetonitri le; substrate/Pd/HCl/H2O = 200-400/1/25-100/500-2000; [Pd] = 0.6-1.2 m mol . l(-1). The reaction rate is approximately of the first order wit h respect to ArCHOHCOOH. The yield increases with the increasing of P- CO and of the temperature, as expected, and passes through a maximum w ith the increasing of the concentration of H2O and of HCl. The propose d catalytic cycle proceeds through the following steps. (i) H2O and CO interact with the metal giving rise to an intermediate having a Pd-CO OH moiety, which, upon beta-hydride abstraction, gives off CO2 with fo rmation of a Pd-H species. (ii) The starting substrate is in equilibri um, in the presence of HCl, with the corresponding chloride ArCHClCOOH , which adds to the metal forming an intermediate having a Pd-CH(Ar) C OOH moiety. (iii) This species interacts with the hydride yielding the product ArCH2COOH and regenerating the catalyst. The reaction is comp ared to the closely related catalyzed water gas shift reaction.