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 H₂ is a very promising route. In this work, we studied the reaction over a number of catalytic systems. It was found that Rh₂(CO)₄Cl₂ 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°C. The TOF was as high as 26.2 h^-1 and the yield of acetic acid could reach 81.8% at 180°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 Rh₂(CO)₄Cl₂, 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.