Reactivity of lignin diphenylmethane model dimers - 1. Nitrobenzene oxidation

A series of unsubstituted phenolic lignin diphenylmethane (DPM)-model dimers of the guaiacyl type has been shown to be quite reactive under alkaline nitrobenzene oxidation conditions resulting in the formation of monomeric products. The yield of vanillin varied considerably with the linkage type (4-32 %), and decreases in the order of alpha-1, alpha-5, alpha-6 and 5,5'-DPM dimers. The reactions also included an oxidation of the a-methylene groups, leading to the formation of diphenylketone derivatives, which were obtained in 5-28% yield. In contrast, the etherified DPM-model dimers were relatively stable under nitrobenzene oxidation conditions.