Molecular Design on Asymmetric Bidentate Chelate Rh(I)-8-Hydroxyquinoline Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid

Based on the theoretical study of the catalytic reaction mechanism, the Rh(I)-8-hydroxyquinoline catalyst was synthesized with 8-hydroxyquinoline as the ligand. Which is a four-coordination molecule with an five-membered ring asymmetric structure containing electron-donating groups. Rh(I)-8-hydroxyquinoline catalyst is used in the reaction of methanol carbonylation to acetic acid. Utilizing the steric hindrance effect of the ligand, Rh(I)-8-hydroxyquinoline fails to form Rh(III) dimers and is difficult to change valence and deactivate, wherefore bidentate complex Rh(I)-8-hydroxyquinoline catalyst with five-membered ring structure has high stability. At the same time, 8-hydroxyquinoline has an asymmetric electron-donating group structure, which effectively reduces the reaction energy barrier of the rate-determining step in the catalytic reaction, which is beneficial to increase the catalytic activity. According to the theoretical results, compared with the industrial rhodium-iodine catalyst system [1] , the rate-determining reaction steps of the Rh(I)-8-hydroxyquinoline catalytic system are significantly reduced, catalyst performance is significantly improved. The acetic acid yield and acetic acid selectivity reaches 100% under certain conditions. Furthermore, during the catalysis, compared with the Rh 2 (CO) 4 Cl 2 catalytic system, the loss of precious metal rhodium is only half of the former. In addition, in the Rh(I)-8-hydroxyquinoline catalytic system, the optimal water consumption is 6 wt%, which is greatly reduced compared with the industrial water consumption (14-16 wt%) for acetic acid production. In summary, Rh(I)-8-hydroxyquinoline catalyst obtained by molecular design has higher catalytic performance than the Monsanto catalyst. What’s more, during the carbonylation reaction of methanol to acetic acid our study shortens the time for catalyst research and development and reduces investment costs.