Effects of acid addition on transfer hydrogenolysis of aromatic ethers in hot-compressed 2-propanol over Ni catalyst

Abstract

The effect of acid additives during transfer hydrogenolysis of aromatic ethers (lignin model compounds) in 2-propanol over a Ni catalyst was investigated. HCl, formic acid, and acetic acid, which have been typically used in organosolv lignin extraction, generally decreased the conversion of aromatic ethers and yields of monomers, indicating an inhibitory effect on transfer hydrogenolysis. Blank experiments demonstrated that acidity (proton release) was the primary reason for the inhibitory effect, but gaseous products from carboxylic acids were also a contributing factor. Comparison of acids revealed that the magnitude of inhibition followed the order HCl > formic acid > acetic acid, which corresponded to the order of their acid strength. Furthermore, the effect was discussed based on the potential proton concentration released from acid additives using their pK_a values.