Sulphite-promoted delignification of wood: identification of paucidisperse lignosulphonates

Abstract

Paucidisperse lignosulphonates, previously described as a distinct group of compounds called "hemilignins" [Formula: see text] were conclusively shown to be a complex mixture of monomeric (C9) sulphonic acids. Since these compounds are rapidly solubilized only during the early stages of delignification from softwoods (≤30% lignin removal), it can be concluded that they are selectively removed from the secondary wall and not from the middle lamella. This result gives chemical support to the hypothesis that morphological differences in lignin structure exist. It is proposed that the generation of monolignols and their sulphonated derivatives may occur via an α-O-aryl bond cleavage rather than β-O-aryl cleavage as previously suggested. For softwoods, several other major constituents were isolated, which may be derived from sulphonation of a β-hydroxylated form of coniferyl alcohol.