Abstract: Benzidine derivatives constitute an important group of toxic and hazardous materials, which are known to be mutagenic, carcinogenic and extensively exsited in the environment. With benzidine as the model organic pollutant, the reaction mechanism of the protonated benzidine-ClO2 reaction in water was studied by gas chromatography-mass spectrometry (GC-MS), ultraviolet–visible spectroscopy (UV-vis) and infrared spectroscopy (IR) techniques. The relationship between presence states of benzidine and the solution pH was proposed. When the pH is lower than 3.57, benzidine presents as bi-proton state. The oxidation immediates and products formed in the reaction of the protonated benzidine with chlorine dioxide (ClO2) in the water were identified at pH 2.0 and the results showed that sequences of the main intermediates were diphenoquinone diimine, diphenoquinone dioxime and diphenoquinone. The end product of the proton state benzidine oxidized by ClO2 was unsaturated organic diacid. Through analyzing the reactions properties of chlorine dioxide with organic compounds and the molecular structure characteristics of benzidine, the possible pathway for the protonated benzidine-ClO2 reaction was proposed based on the theory of single electron transfer (SET).

Key words:
benzidine, chlorine dioxide, proton state, intermediate, reaction mechanism