Use of Bisulfite Processing To Generate High-β-O-4 Content Water-Soluble Lignosulfonates

With lignin-first biorefineries likely to become a reality, controlled depolymerization of high-quality lignin streams to high-value products has become a priority. Using bisulfite chemistry, access to a high-β-O-4 content water-soluble lignosulfonate has been achieved, allowing follow-up procedures in water to be conducted. We show that phenolic β-O-4 units preferentially react under acidic bisulfite conditions, while nonphenolic β-O-4 units react much more slowly. Exploiting this improved chemical understanding and inherent selectivity, we have prepared a softwood lignosulfonate in which phenolic β-O-4 α-sulfonation has occurred, leaving significant native β-O-4 content. Use of an O-benzoylation protocol with lignin coupled with advanced two-dimensional nuclear magnetic resonance methods has allowed detailed analysis of this and other commercial and industrial lignosulfonates. Conversion of the native β-O-4 to benzylic, oxidized β-O-4 units was followed by a selective reductive cleavage to give a premium aromatic monomer in pure form.