Oxidation reaction of high molecular weight dicarboxylic acids in sub- and supercritical water

Sebacic and azelaic acids, which are representative of high molecular weight dicarboxylic acids, were oxidized in a batch reactor with H₂O₂ oxidant in water from 300 °C to 400 °C at sub- and supercritical conditions. Intermediate products were identified based on GC-MS, HPLC, and ¹H NMR. The main oxidation products were dicarboxylic acids and the minor products were monocarboxylic acids. (ω - 1)-Keto acids, aldehyde-acids, and γ-lactones with carboxylic groups also were identified. On the basis of the products identified, the oxidation pathways of high molecular weight dicarboxylic acids were formulated. The oxidation of high molecular weight dicarboxylic acids proceed with the consecutive oxidation of higher to lower molecular weight dicarboxylic acids mainly through the oxidation at α-, β-, and γ-carbons to a -COOH group. The oxidation of dicarboxylic acids was also accompanied by oxidative decarboxylation, leading to the formation of monocarboxylic acids.