Pyrolysis and combustion of cellulose. II. Thermal analysis of mixtures of methyl α‐D‐glucopyranoside and levoglucosan with model phosphate flame retardants

The thermal degradation of methyl α-D-glucopyranoside, a cellulose model of intermediate complexity, was investigated in an attempt to gain insight into the pyrolytic reactions of analogous cellulose systems. The pure glucoside pyrolysis proceeds through formation of an intermediate of higher thermal stability. Nitrogenous bases bring about decomposition of the glucoside at lower temperatures and without formation of a detectable intermediate. Phenyl phosphates and phosphoramides induce thermal degradation of methyl α-D-glucopyranoside at lower temperatures than observed for the pure glucoside. The postulated degradation mechanism involves esterification of the glucoside followed by dehydration and skeletal rearrangements. Nitrogenous bases assist the dehydration process but reduce the yield of residue and bound phosphorus. Levoglucosan, the cellulose degradation product responsible for flaming combustion, was pyrolyzed in the presence of model flame retardants. Nitrogenous bases were found to inhibit thermal polymerization of levoglucosan and to induce its decomposition at lower temperatures. Zinc chloride exerted its effects in two stages: acid-catalyzed polymerization at lower temperatures and dehydration at higher temperatures. Phenyl phosphates and phosphoramides alter levoglucosan pyrolysis by action as Lewis acids in a manner similar to zinc chloride.