Electrocatalytic reduction of arylethyl chlorides at silver cathodes in the presence of carbon dioxide: Synthesis of 2-arylpropanoic acids

The electrochemical reduction of some arylethyl chlorides ArCH(CH3)Cl (Ar = 4-isobutylphenyl, 3-phenoxyphenyl, 6-methoxy-2-naphthyl), which are used as precursors in the electrosynthesis of important anti-inflammatory drugs, has been investigated at Ag and glassy carbon (GC) electrodes in CH3CN and DMF. In both solvents Ag shows a remarkable catalytic effect for the electroreduction of the halides. The Ep values obtained at this electrode are 0.34-0.55 V more positive than those obtained at GC. The electrocatalytic effect of Ag is further enhanced by the presence of CO2, the observed positive Ep shift increasing up to 0.55-0.76 V in CO2-saturated solvents. The mechanism of the electrochemical reduction of the halides at both electrodes is discussed. Large scale reduction of ArCH(CH3)Cl at Ag carried out in CO2-saturated solvents at 298.15 and 273.15 K led to the formation of ArCH(CH3)CO2H as the principal product. Although satisfactory acid yields were obtained in both cases, better results were obtained at the lower temperature; the acid yields were 61-73% and 70-81% at 298.15 and 273.15 K, respectively.