Highly Efficient Direct Carboxylation of Propane into Butyric Acids Catalyzed by Vanadium Complexes

A direct and highly efficient carboxylation of propane by carbon monoxide into butyric acids (mainly isobutyric and, in a smaller amount, n ‐butyric), in the presence of potassium peroxodisulphate (K 2 S 2 O 8 ) and in trifluoroacetic acid solution, has been achieved by using a vanadium catalytic system based on Ca[V{ON(CH(CH 3 )COO) 2 } 2 ] (synthetic amavadine ), its model compounds Ca[V{ON(CH 2 COO) 2 } 2 ] or [VO{N(CH 2 CH 2 O) 3 }] – other simpler vanadium compounds, such as [VO(acac) 2 ] or VOSO 4 , are less active. Overall yields (based on propane) of carboxylic acids up to 70 % and TON values up to 18.4×10 3 have been reached. The effects of various factors such as the propane and carbon monoxide pressures, temperature, time, catalyst amount and radical traps have been investigated, the reactions are shown to proceed v ia both C ‐ and O ‐centred radicals, with K 2 S 2 O 8 playing the role of an oxidant via a free radical mechanism.