Stereoselective hydrogenation of guaiacol to cis-2-methoxycyclohexanol using supported rhodium catalysts in supercritical carbon dioxide

Selective hydrogenation of lignin-derived phenolic monomer to valuable chemicals has attracted attention and investigated well; however, stereoselective hydrogenation is required for practical applications, and is still challenging. In this study, we examined the stereoselective hydrogenation of guaiacol to cis-2-methoxycyclohexanol over supported metal catalysts in several solvents at mild reaction conditions. Rh/C in supercritical CO2 gave a higher proportion of cis-2-methoxycyclohexanol in total 2-methoxycyclohexanol compared to water solvent. Finally, guaiacol could be stereoselectively hydrogenated to cis-2-methoxycyclohexanol with the yield 83.9 % (total 2-methoxycyclohexanol yield was 95.5 %) even at 313 K for 1 h using the Rh/C catalyst in supercritical CO2 (CO2 25 MPa, H2 1.5 MPa).