Selective Hydrogenation of 4‐Substituted Phenols to the Cyclohexanone Analogues – Catalyst Optimization and Kinetics

Abstract

4‐position substituted cyclohexanones are of great importance as key intermediates for the synthesis of liquid‐crystal materials. Unsubstituted cyclohexanone can be manufactured by the selective hydrogenation of phenol. Industrial processes exist, in which phenol is hydrogenated by a heterogeneous catalyst in the vapor or liquid phase melt with high selectivity leading to high amounts of cyclohexanone. However, very little kinetic data exists to date for the selective hydrogenation of phenol and the cresols in an inert solvent. The aim of this work is to optimize the selective liquid‐phase hydrogenation of 4‐(4′‐trans‐n‐propylcyclohexyl)‐phenol.

Selective hydrogenation of phenol and related derivatives

“…Vogel et al found that palladium-on-charcoal, modified with sodium carbonate, hydrogenates 4-(4-propylcyclohexyl)-phenol to the corresponding cyclohexanone derivative effectively in a non-polar solvent. 134 It was suggested that the substrate and target product do not compete for the catalytically active sites, which is inconsistent with the results obtained by Gut et al 135 and Nishimura et al 43,136 Li et al pointed out that the hydrogen reduction method leads to a better Pd dispersion and a higher catalytic activity compared with the formaldehyde reduction method. Besides, K and Sn dopants enhance the 4-(4-proplycyclohexyl)-phenol conversion rate and the selectivity to 4-(4-proplycyclohexyl)-cyclohexanone.…”