THE REACTION OF PHLOROGLUCINOL IN THE PRESENCE OF ACID WITH LIGNIN-CONTAINING MATERIALS

UV-visible diffuse reflectance spectrometry has been used to monitor t he reaction of phloroglucinol (in the presence of hydrochloric acid) w ith high yield pulps. When papers made from such pulps are irradiated, coniferaldehyde residues are generated as judged by their reaction wi th phloroglucinol/HCl. Treatment of such papers with sodium borohydrid e reduces the coniferaldehyde residues and consequently no colour reac tion with phloroglucinol/HCl is observed. Irradiation of these borohyd ride-reduced papers leads to the generation of coniferaldehyde entitie s as detected by phloroglucinol/HCl. Similar results were obtained usi ng a thin section of abies wood. Irradiation of papers made from high yield pulps destroys coniferaldehyde residues on the one hand and gene rates them from other sources on the other hand. Examination of papers made from the morphological components of poplar showed that it is im possible to quantify the amount of lignin present by this colour test method. Thioacidolysis analysis of the fractions shows for all of them a higher proportion of syringyl than guaiacyl beta-O-4 aryl ether lin kages. In contrast, photocleavage of the beta-O-4 aryl ether linkages is more important for the guaiacyl structures. This is in accordance w ith the observed higher sensitivity to UV light of softwood pulps comp ared with hardwood pulps. Also, the thioacidolysis experiments indicat e that UV irradiation of the fractions maintains a stationary concentr ation of the coniferaldehyde structures.