Abstract
Photodecomposition of chinomethionat (S, S-6-methylquinoxaline-2, 3-diyl dithiocarbonate, Morestan®) was remarkably accelerated by natural unsaturated fatty acids such as oleic acid. The accelerating effect was based on the unsaturated double bond. In the homologous series of unsaturated fatty acids, increase in number of double bonds resulted in more enhanced photodecomposition of chinomethionat. Accelerating activity of normal chain unsaturated fatty acids with a double bond increased with the decrease in the length of carbon chain and with the increase of carbon chains between the double bond and carboxyl group. Among the structural isomers of unsaturated fatty acids, cis-forms showed much higher accelerating activity in comparison with trans-forms. The photodecomposition of chinomethionat was also accelerated by non-ionic surfactants and fatty oils containing unsaturated fatty acid moiety. Chinomethionat was almost completely decomposed by irradiation with UV light for 24hr when oleic acid was added over 23 times in molar ratio. The photodecomposition of anilazine, chlomethoxynil, chlornitrofen, chlorothalonil, dichlozoline, dicofol and procymidone was also accelerated in the presence of oleic acid, among other 26 pesticides tested.
