Efficient synthesis of acetic acid via Rh catalyzed methanol hydrocarboxylation with CO2 and H2 under milder conditions

Acetic acid is an important bulk chemical and synthesis of acetic acid via methanol hydrocarboxylation with CO2 and H-2 is a very promising route. In this work, we studied the reaction over a number of catalytic systems. It was found that Rh-2(CO)(4)Cl-2 with 4-methylimidazole (4-MI) as the ligand was very efficient in the presence of LiCl and LiI. Acetic acid began to form at 150 degrees C. The TOF was as high as 26.2 h(-1) and the yield of acetic acid could reach 81.8% at 180 degrees C. The catalytic system had obvious advantages, such as simplicity, high activity and selectivity, milder reaction conditions, and less corrosiveness. The excellent cooperation of CO and Cl-in Rh-2(CO)(4)Cl-2, suitable basicity and aromaticity of the ligand 4-MI, and the hydrogen bonding ability of Cl-were crucial for the outstanding performance of the catalytic system. The control experiments showed that the reaction did not proceed via the CO pathway.