Structure of oxidized hydrolysis lignin

The main goal of this study was the elucidation of structures of products of oxidation of industrial hydrolysis lignin (HL) obtained in the system H2O2-H2SO4-H2O. It was found that the obtained oxidized hydrolysis lignin (OHL) contained structural fragments of muconic acid dilactone. The latter appeared as a result of the oxidation of aromatic ring of HL into unstable structures of 3,4-dihydroxyadipic acid, which are spontaneously cyclized into the corresponding fragments of muconic acid dilactone in acidic oxidative medium. Consequent reaction of OHL with aqueous sodium hydroxide (NaOH) led to the formation of sodium salt of OHL (Na-OHL), in which the muconic acid dilactone units of OHL opened into fragments of disodium salts of 3,4-dihydroxyadipic acid. The Na-OHL was transformed into the series of novel derivatives of lignins. Thus, the reaction of Na-OHL with thionyl chloride proceeded as a substitution of hydroxyl groups into chlorine atoms in the structure of OHL, that afforded chloro-derivative of OHL. The latter was transformed into amino-amide and ester-ether derivatives of OHL by nucleophilic substitution of chlorine atoms with amines and alcohols correspondingly.

Automated summary

The objective of this study was to determine the structures of oxidation products of hydrolysis lignin (HL) obtained in the H2O2-H2SO4-H2O system. The results revealed that the oxidized hydrolysis lignin (OHL) contained fragments of muconic acid dilactone. These fragments were formed through the oxidation of the aromatic ring of HL into unstable structures of 3,4-dihydroxyadipic acid, which cyclized into muconic acid dilactone in an acidic oxidative medium. Reaction of OHL with sodium hydroxide (NaOH) resulted in the formation of sodium salt of OHL (Na-OHL), in which the muconic acid dilactone units of OHL opened into disodium salts of 3,4-dihydroxyadipic acid. Na-OHL was further transformed into novel derivatives of lignins through reactions with thionyl chloride, amines, and alcohols.