REACTION PATTERNS IN PHOTOOXIDATIVE DEGRADATION OF 2 HERBICIDES

Different reaction patterns of photooxidation has been witnessed for t he herbicides metribuzin, tyl-4,5-dihydro-3-methylthio-1,2,4-triazine- 5-one) and bromacil (5-bromo-3-sec-butyl-6-methyluracil). In the first case oxygen has a pronounced effect on the rate of photooxidation, wh ile the influence of hydrogen peroxide is quite moderate. The photolyt ic process in this case would apparently start via a reaction of the e xcited herbicide molecule with hydrogen peroxide or with oxygen. In an other case, exemplified by bromacil, oxygen does not have a pronounced effect on the rate of photooxidation, which however is considerably e nhanced by hydrogen peroxide. The reaction is initiated by hydroxyl ra dicals generated by hydrogen peroxide photolysis. These conclusions ar e supported by the different effects of isopropanol inhibition. (C) 19 98 Elsevier Science Ltd.