Photochemical oxidation of γ-exachlorocyclohexane and 4,4’- dichlorodiphenyldichloroethylene

Objectives: Utilization of the forbidden organochlorine pesticides demands searching of new ways of their neutralization. In such way there can be a photochemical oxidation of pesticides. As a research objects we chose γ-hexachlorocyclohexane (lindane) and 4,4 '- dichlorodiphenyldichloroethylene (DDE). Radiation treatment of solution is carried out by the UF-lamp with a wavelength of 254 nanometers.

Methods: Residual concentrations of pesticides were determined by "Lyumakhrom" liquid chromatograph. The infrared spectrum of initial lindane, DDE solutions in the process of photochemical oxidation of pesticides by hydrogen peroxide is observed in ZnSe precision cell by Infrared Fourier Transform Spectroscopy "Infralyum of FT-02". The kinetics of photochemical oxidation process of γ-hexachlorocyclohexane (lindane) and 4,4 '- dichlorodiphenyldichloroethylene (DDE) is studied.

Findings: The analysis of obtained results shows that use of the homogeneous catalysts, initiating the process of H2O2 and H2O photolysis, reduces the concentration of lindane and DDE in the first hour of treatment. Without catalyst the residual concentration of lindane is 0,289×10-6 mol/dm3, DDE – 0,235×10-6mol/dm3, while addition of iron (III) to H2O2 leads lindane concentration dilution up to 0,029×10-6 mol/dm3, DDE – to 0,046×10-6 mol/dm3. Addition as the Zn (II) catalyst to hydrogen peroxide decreases the concentration of lindane to 0,129×10-6 mol/dm3, DDE – to 0,163×10-6 mol/dm3 in 2 hours. In the presence of iron ions (III) as the homogeneous catalyst initiating the photolysis of hydrogen peroxide and water, the constant rates are increased by six times. The analysis of pesticides photochemical oxidation products by IR spectrums allowed assuming mechanisms of photochemical oxidation of pesticides by hydrogen peroxide. As may be supposed, there is a cycle rupturing in lindane leading to formation of the aliphatic ketones which are restored to secondary alcohols; and DDE have a rupture of C (1) atom benzene ring with formation of chlorophenols and alkenes. From then on chlorophenols are oxidized by hydroxyl radical to the carbon dioxide and water, and alkenes are hydrated to primary alcohols.

Conclusion: The conducted research showed high efficiency of photochemical oxidation process of pesticides in the presence of homogeneous catalyst – iron ions (III).