Lignin and related compounds. VIII. Lignin monomers and dimers from hydrogenolysis of aspen poplar wood using rhodium-on-charcoal catalyst

Abstract

Aspen poplar wood meal has been subjected to catalytic hydrogenolysis in dioxane–water (9:1) at 500 psig initial pressure of hydrogen over a 5% rhodium-on-charcoal catalyst for five hours at 195 + 5 °C. The resulting chloroform-soluble lignin degradation products were separated by cellulose and silica gel column chromatography. The following compounds were isolated and identified: 4-hydroxybenzoic acid (5), 1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (propiosyringone) (6), 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dipropylbiphenyl (7), 2,3-bis(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (11), and a mixture of 3-(4-hydroxy-3,5-dimethoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1-propanol (9) and 3-(4-hydroxy-3-methoxyphenyl)-2-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (10).