Mild and highly selective hydrogenation of cyclohexyl acetate to cyclohexanol over Cu(i) coordinated amino-functionalized poly(ionic liquid)s

Abstract

A novel, efficient and economical process of cyclohexanol (CHOL) production based on cyclohexene esterification–hydrogenation has become a research hotspot in recent years. Wherein, hydrogenation of cyclohexyl acetate (CHA) derived from the esterification of cyclohexene with acetic acid is a crucial step. Combining the advantages of metal complexes and heterogeneous catalysts, the robust Cu(I) coordinated amino-functionalized poly(ionic liquid)s (PILs-Cu(I)) were, in this research, synthesized for use in the mild and highly selective hydrogenation of CHA to CHOL. The results of FT-IR, UV-vis, BET, XPS and SEM-EDS confirmed that the Cu(I) was dominant in the PILs-Cu(I), and was homogeneously and stably coordinated on the amino-functionalized poly(ionic liquid)s. Benefiting from that, the PILs-Cu(I) was endowed with an unprecedented performance in the mild and highly selective hydrogenation of CHA to CHOL. Specifically, 95.6% CHA conversion with 96.6% selectivity of CHOL, and 97.0% selectivity of ethanol was obtained under extremely mild conditions of 80 °C and 2 MPa H₂. Furthermore, no significant activity loss was observed over the PILs-Cu(I) after recycling for at least five times, delivering excellent stability and reusability.