Sulfation of Abies Ethanol Lignin by Complexes of Sulfur Trioxide with 1,4-Dioxane and Pyridine

An optimization of sulfation of abies ethanol lignin by complexes of sulfuric anhydride with pyridine and 1,4-dioxane has been performed. Conditions for the implementation of the sulfation of abies ethanol lignin by complexes of sulfur trioxide with 1,4-dioxane and pyridine that provide a high sulfur content (12.0–12.6%) have been experimentally found. It has been shown that a high sulfur content of 12.0–13.5% (mass) in the resulting ethanol lignin sulfate is achieved at a chlorosulfonic acid to ethanol lignin ratio of 20.22 : 1 mmol : g and a duration of the process of 60–120 min and does not depend on the origin of the sulfation complex. The structure and the composition of water-soluble sulfated ethanol lignin have been confirmed by FTIR spectroscopy, gel-permeation chromatography, and elemental analysis. The IR spectra of sulfated abies ethanol lignin, as compared with the IR spectra of initial ethanol lignin, have absorption bands in the regions of 1270–1260, 1220–1212, and 861–803 cm–1, which correspond to the vibrations of sulfate groups. Sulfated ethanol lignin from abies wood has a low degree of polydispersity as compared with initial lignin. In particular, an increase in Mw from ~1.5 to ~3.4 kDa in lignin sulfated for 30 min and a decrease in polydispersity from 2.59 to 1.22 in comparison with the initial ethanol lignin were observed. As the time of sulfation increased, the profile of the curve of the molecular weight distribution shifted toward the high-molecular-weight region with a simultaneous increase in polydispersity to 1.5 and in the mean molecular weight to ~4.3 kDa.