Monitoring of free phenol content in lignosulfonates by ClO2 titration and UV difference spectroscopy

Lignosulfonates (LS) are water-soluble polyphenolic macromolecules derived from lignins and common industrial additives in plasticizers and dispersants. A key feature for a more efficient utilization of modified LS is the monitoring of their free phenol (OH ) content during various reactions as these phenols govern a large part of their chemical reactivity. Against this background, the UV difference spectroscopy (Δε method) and ClO titration have been revisited. Synthetic LS model compounds with a SO H group on their benzylic position and H, G, and S aromatic rings were synthesized and used to assess the suitability of both the ClO titration and the Δε method on LS. The methodology combining the two analytical methods was then used to determine the molar extinction coefficient of a given LS allowing the calibration of the Δε method for a convenient and rapid monitoring of OH in the course of LS reactions involving the OH groups.