Facilitation of aldol condensation for lignin alkaline cupric (II) oxidation products having long-wavelength UV absorption

Abstract

The purpose of this study is the efficient production of long-wavelength UV absorbing lignin oligomers by accelerating their formation reactions. In previous study, several oligomers were isolated from lignin alkaline cupric (II) oxide (CuO) oxidative degradation products and were expected to be used in value-added applications. Some of these lignin oligomers are estimated to be formed via aldol condensation reactions between lignin degradation monomers and acetone. For efficient production, acetone was added as a raw material to hardwood alkaline CuO oxidative degradation system. As a result of acetone addition, the yields of oligomers in the lignin degradation products increased as the amount of acetone increase. LC-MS analysis of the degradation products showed that aldol condensation products were increased compared to the without acetone. Furthermore, a model experiment was conducted that vanillin and syringaldehyde were used as lignin degradation product models. This experiment showed that the addition of acetone to the lignin alkaline CuO oxidative degradation system promoted the aldol condensation reaction due to the formation of dehydrozingerone.