N. Hiyoshi, C. Rode, O. Sato
Nov 15, 2007
Citations
0
Influential Citations
29
Citations
Journal
Journal of Catalysis
Abstract
Abstract Hydrogenation of 2-, 3-, and 4- tert -butylphenols was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide (scCO 2 ) solvent, and the results were compared with those in organic solvents. In the hydrogenation of 4- tert -butylphenol, a higher cis ratio for 4- tert -butylcyclohexanol (0.79) was obtained in scCO 2 (10 MPa) than in 2-propanol (0.70) and cyclohexane (0.64) under similar conditions of hydrogen pressure (2 MPa) and temperature (313 K). In the case of 2- tert -butylphenol, the cis ratio for 2- tert -butylcyclohexanol was as high as 0.95 in both scCO 2 and 2-propanol (hydrogen pressure, 2 MPa; reaction temperature, 313 K). In the case of hydrogenation of 3- tert -butylphenol, the cis ratio decreased with the progression of consecutive hydrogenation of 3- tert -butylcyclohexanone intermediate. In addition, the stereoselectivity to cis - tert -butylcyclohexanols in scCO 2 was improved in the presence of hydrochloric acid. It was found that the protons of hydrochloric acid accelerated the hydrogenation of the intermediates, tert -butylcyclohexanones, to the corresponding cis - tert -butylcyclohexanols. The hydrogenation mechanism of tert -butylphenols, particularly the enhanced selectivity to cis - tert -butylcyclohexanols in scCO 2 , is postulated based on the observed reaction profiles.