Stereoselective hydrogenation of 4-alkylphenols over carbon-supported rhodium catalyst in supercritical carbon dioxide solvent

Hydrogenation of 4-alkylphenols was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide (scCO2) solvent, and the results were compared with those in 2-propanol. Higher selectivities to cis-4-alkylcyclohexanols were obtained in scCO2 than in 2-propanol for the hydrogenation of all 4-alkylphenols tested. In addition, the formation of alkylcyclohexane (dehydroxylated product) was suppressed in scCO2. Stereoselectivities to cis forms were further improved in the presence of hydrochloric acid.