Comparative studies of chlorine dioxide reactions with muconic acid derivatives and lignin model compounds

The reaction of chlorine dioxide with different types of lignin model compounds was investigated in order to compare the kinetics and to evaluate the amount of oxidant consumed by the different substrates. Complete reaction of lignin model compounds was observed at ClO2-to-substrate molar ratios of 0.9-1.2, which corresponds to an electron transfer varying between 5-6 equivalents per mole of substrate. Muconic acid derivatives also fully reacted, at a ClO2-to-substrate molar ratio of 1.2, with the oxidant consumption being about 4 equivalents per mole of substrate. The reaction of mixtures of phenolic, non-phenolic, and muconic acid type substrates showed that the reaction rates of non-phenolic and muconic acid type substrates were rather similar. This study suggests that further reaction between ClO2 and the primary lignin oxidation products, such as muconic acid type structures could be the cause of overconsumption of oxidant in a D stage.