The oxidative carbonylation of benzotrifluoride to form trifluoromethylbenzoic acid (TFMBA) has been catalyzed using either Rh(Ill) or a Pd(II) cation in combination with a carboxylic acid and its anhydride, ammonium metavanadate, CO, and O-2. The influence of metal cation and vanadate concentrations, temperature, time, acid composition, and gas pressures, were explored. The accumulated data suggest that oxidative carbonylation of benzotrifluoride proceeds via an electrophilic mechanism. Rh-catalyzed reactions exhibited higher activity (similar to 70 turnovers in 4 h at 353 K) and trifluoromethylbenzoic acid selectivity (similar to 92-95%) than Pd-catalyzed reactions (similar to 6 turnovers in 4 h at 353 K and a trifluoromethylbenzoic acid selectivity of 80%). Formation of the principle reaction byproducts, benzoyl fluoride and benzoic acid, was highly dependant on the V(V) concentration and the acid composition. Reactions conducted in the presence of CF3COOH yielded the highest catalytic activity. but reactions conducted in CCl3COOH resulted in the highest trifluoromethylbenzoic acid selectivity. A possible mechanism for the reaction has been proposed. (C) 2008 Elsevier B.V. All rights reserved.