Acylation of humic acids

A method for the chemical modification of humic acids with benzoyl chloride under the conditions of phase-transfer catalysis was developed. It was demonstrated by potentiometric titration that the reaction of humic acids with benzoyl chloride can occur at both hydroxyl (–OH) and carboxyl (–COOH) groups. The antioxidant activity of the initial humic acids and their chemical modification products in radical-chain oxidation processes in an organic medium was determined by a gas-volumetric method. A decrease in the antioxidant activity of the acylated humic acids in comparison with that of the native forms was found; this can be related to a decrease in the amount of active functional groups (–OH,–NH, and–SH) due to binding with benzoyl chloride.