Triazines hexazinon

CyclohexyT6-amino-l -methyl-s-triazine-2,4(l//,3/4dione, see Hexazinone... 

Hexazinone is subject to microbial degradation (Rhodes, 1980 Feng, 1987). Metabolites identified in soils, alfalfa, and/or sugarcane include 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1 -methyl-s-triazine-2,4 (1 //, 3/7) dione, 3-cyclohexyl-6- (methylamino) -1 -methyl-5-triazine-2,4-... 

Feng (1987) monitored the persistence and degradation of hexazinone in a silt loam soil 104 d after treatment of the herbicide. After 104 d, 66% of the hexazinone degraded via hydroxylation to form the major metabolite 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-l-methyl-s-triazine-2,4(l//,3//)dione (30-50% yield). A minor metabolite, 3-cyclohexyl-6-(methylamino)-1-methyl-s-triazine-2,4(1//,3//)-dione, forming via demethylation, accounted for only 0-12% of the applied herbicide. Hexazinone and its metabolites were not detected in soils at depths of 15-30 cm. 

Changing the nature of the triazine substitution pattern to the l,3,5-triazine-2,4-dione system leads to another series of herbicides, of which the best example is hexazinone (1) (75USP3902887). It is built up from cyanamide which is converted in several steps to the guanidine (2). Reaction with cyclohexyl isocyanate then gives an intermediate which can be cyclized to hexazinone (Scheme 2). 

The triazine herbicides can be divided into four different structural classes chlorotriazines, methylthiotriazines, methoxytriazines, and atypical or asymmetrical triazines. The chlorotriazine group includes atrazine, simazine, pro-pazine, terbuthylazine, and cyanazine. The methylthiotriazine group includes ametryn, prometryn, and terbutryn. The methoxytriazine group will include prometon and secbumeton. Hexazinone and metribuzin were chosen to represent the atypical triazine group. The plant metabolism of the most researched member of each triazine group will be discussed in detail to cover all major biological and chemical transformations reported in the literature. 

The triazine herbicides simazine, atrazine, and hexazinone are commonly used in Christmas tree plantings in North America. Hexazinone is widely used in certain pines and on other conifer species in natural stands in regions where the organic matter content in soil is adequate to prevent excessive leaching to conifer root zones. Simazine and... 

Triazine herbicides are primarily effective in controlling herbaceous weeds. A notable exception is the use of granular hexazinone for controlling woody invaders such as oaks (Quercus spp.) or aspen (Populus tremuloides) in conifer stands on medium- and fine-textured soils in the South or in boreal forests. Hexazinone also is used in the Maritime Provinces of Canada for controlling woody and herbaceous growth in natural Christmas tree stands (Townsend, 1995a). The impact of herbaceous plant cover is somewhat different from that of woody plant competitors, so control strategies on various forest conifer sites may differ. 

Hexazinone is relatively mobile in coarse- to medium-textured forest soils under the influence of abundant moisture (Newton and Cole, 1997), and its penetration deeper in soil facilitates control of perennials, several shrubs, and hardwoods (Minogue et al., 1988 Quicke et al., 1996). It has replaced other triazines on sites where woody as well as herbaceous competitors are important. 

Several processes may play a role in the environmental dissipation of -triazine herbicides. Dissipation processes can include microbial or chemical degradation in soil metabolism or conjugation in plants photodegradation in air, water, and on soil and plant surfaces and volatilization and transport mechanisms. This chapter will address photolytic degradation and abiotic hydrolysis of the currently used triazine herbicides, the triazinone herbicides (metribuzin and metamitron), and the triazinedione herbicide hexazinone. 

Under the pH and temperature conditions of natural waters, the various 2-chloro-, 2-methylthio-, and 2-methoxy-.v-triazine herbicides are generally considered to be stable in solution between pH 5 and pH 9, stable in neutral, weakly acidic and weakly alkaline media, and stable to hydrolysis at 20°C in neutral, weakly acidic, and weakly alkaline media (Pesticide Manual, 1997). Metribuzin, metamitron, and hexazinone are also considered to be stable under these conditions (Pesticide Manual, 1997). Such hydrolytic stability of the triazine herbicides is supported by hydrolysis studies (Rhodes, 1980 Widmer et al., 1993 Noblet et al, 1996 Hequet et al, 1997) that indicate either very slow rates of hydrolysis or no measurable hydrolysis (Table 23.3) under these conditions. 

Aquatic animals were less sensitive to the triazines than were aquatic plants. Toxicity to fish and arthropods varied, with fish or crustaceans sharing the position of most sensitive aquatic animal, depending on the herbicide. In the case of atrazine, arthropods were generally more sensitive than fish. Ratios of the 10th centiles between animals and plants were varied. The animal/plant ratio for atrazine (arthropods) was 24, while hexazinone was 202800. The hexazinone data were from a small data set, and the atrazine data were for arthropods and could not be compared to data for the other triazines. However, the ratios for the other triazines also varied over an order of magnitude, from 176 for prometon to 1688 for prometryn. Since the molecular weights of the triazines are similar, one would expect their... 

Hexazinone heterocyclic nitrogen, triazine Hexythiazox thiazolidine, amide Hydramethylnon heterocyclic nitrogen, pyrimidine Hydroprene dienedodecanoate 8-Hydroxyquinoline sulphate heterocyclic nitrogen, quinoline... 

An elimination of ammonia from LXXXIV to purine followed by reduction of the latter may also be possible [468] such a reduction route is analogous to that of 4-amino-quinazoline in acid solution [409], in which quinazoline can be detected as an intermediate during the reduction. A similar reaction, a reduction followed by elimination of an amine and further reduction is found for the herbizide hexazinone (3-cyclohexyl-6-(dimethyla-mino)-1 -methyl-1.3.5-triazine-2,4( 1 H,3H)-dione [469]. 

The triazine herbicides are based on an s-triazine structure containing two amino groups. Atrazine, simazine and terbutryne present an absorption peak around 225 nm (Fig. 55), whereas hexazinone (Fig. 56) has an absorption maximum at 248 nm. 

Many studies for pesticides in soil have been carried out for triazines. Other analytes include carbofuran/ chlorpyrifos/ hexazinone/ metolachlor/ 4-nitrophenol/ and triasul-... 

Hexazinone is a representative of another family of herbicidal 1,3,5-triazines, which are characterized by the presence of a cyclic urea feature. It may be synthesized as in Scheme 11.3 by condensing guanidine derivative 11.1 and cyclohexyl isocyanate to form intermediate 11.2, which is then cyclized by the NH-to-ester condensation found frequently in pyrimidine synthesis to give hexazinone (11.3). 

The 1,2,4-triazinones [25], metamitron (Bayer, 1975) and metribuzin (Bayer, Du Pont, 1971) and the l,3,5-triazine-2,4(lH,3H)-dione [26] hexazinone (Du Pont, 1975), resulted first from the resynthesis of university publications or analogue synthesis using uracils as starting ideas. 

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