Two new structural classes of herbicide have been discovered which are based on the 1,2,4-triazolo[1,5-a]pyrimidine ring system. These compounds are related to the known herbicidal sulfonylureas and imidazolinones and other studies have shown that they have a similar mode of action, involving the inhibition of branched-chain amino acid biosynthesis, the site of action beingthe enzyme acetolactate synthase. The design, synthesis and structureactivity relationships of these new classes of compounds are described.

Abstract. The hydrolysis rate of chlorpyrffos (the active ingredient of DURS-BAN @ and LORSBAN | insecticides, registered trademarks of The Dow Chemical Company, Midland, Michigan) in water followed simple first-order kinetics over the concentration range, 3 x 10 -9 to 3 x 10-ZM. In buffered distilled water at 25~ and pH 8. I, 6.9, and 4.7, the haft-life was 22.8, 35.3, and 62.7 days, respectively. Additional data were obtained for rates at 15 ~ and 35~ The activation energy for the reaction under these conditions was 21.2 kcal/mole. A 16-fold rate enhancement was demonstrated in canal and pond water at 25~ Likewise, there was a catalytic effect on the hydrolysis rate in the presence of copper (II) ion.The same information was generated for chlorpyrffos-methyl, the dimethyl analog of chlorpyrifos. In this case, the corresponding "half-life values for hydrolysis at 25~ and pH 7.8, 6.7, and 4.2 were 12.7, 17.4, and 22.8 days, respectively. The activation energy was 20.8 kcal/mole, not significantly different from that for chlorpyrffos. A hydrolysis rate enhancement also occurred for chlorpyrifos-methyl in canal water.Qualitatively, the products of chlorpyrifos hydrolysis were 3,5,6-trichloro-2-pyridinol (I), O-ethyl O-hydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (II), and O, O-dihydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (III). In the case of chlorpyritbs-methyl, the hydrolysis products were compound I and the methyl analog of compound II.Because of the need to evaluate the fate of pesticides in the environment to which they may be applied, a study was carried out to determine the fate of chlorpyrifos in water. The efficacy of this compound has been well demonstrated (Collier and Dieter 1965, Gray 1965, Kenaga et al. 1965. The dimethyl analog, chlorpyrifosmethyl, was included in this study. The investigation reported herein defines the hydrolysis rates at different pH and temperature values, gives the observed activation energy for the reaction, and describes the hydrolysis products.

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We have shown by means of laboratory experiments with a wide range of soil types that the decomposition rate of picloram (4-amino-3,5,6-trichloropicolinic acid) in soil is dependent on soil temperature and moisture content and to no significant extent on organic matter, sand, silt, clay, pH, or initial concentration. A fractional order rate law (0.8) describes the disappearance rate best. It was not possible to develop a suitably precise equation for prediction of loss rate as affected by the above soil and climatic factors. Application of the Arrhenius equation to the data indicates an activation energy of 5.4 kcal/mol for the decomposition of picloram in soil, thus suggesting that the reaction is biological rather than chemical.

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