Double-metal cyanide as an acid and hydrogenation catalyst for the highly selective ring-rearrangement of biomass-derived furfuryl alcohol to cyclopentenone compounds
Herein, novel green synthetic routes to 4-hydroxy-2-cyclopentenone (HCP) and 2-cyclopentenone (CPE) from biomass-derived furfuryl alcohol via double-metal cyanide catalysis are proposed. For the synthesis of HCP, in comparison to conventional solid acids (i.e., amberlyst-15), MOFs with coordinatively unsaturated metal ions as pure Lewis acid sites exhibit advantageous catalytic selectivity in the reaction under an N2 atmosphere in a bi-phasic water/n-hexane solvent system. FeZn and FeZn-P result in an HCP yield of 77.4% and 88.2%, respectively. For the CPE synthesis, the reaction conditions are the same as those for HCP, except a mono-phasic water solvent system and H2 atmosphere were employed. In addition to the acid-catalyzed rearrangement reaction, FeZn-DMC exhibits catalytic hydrogenation capability via heterolytic cleavage of the H-H bond over Zn-N frustrated Lewis pairs, and a CPE yield of 61.5% is obtained. The DFT simulation indicates that the acid sites and catalytic acid sites are ascribed to the tri-coordinatively unsaturated Zn2+ site (Zn(N)3) on the catalyst surface. Moreover, the DMC catalyst shows excellent stability and recycling performance. This work not only provides an efficient and green catalytic system for CPE and HCP preparation but also demonstrates the interesting bifunctional catalysis of both acid and hydrogenation catalysis over DMC.