Herbicides chloroxuron

PCDEs are used as intermediates in chemical syntheses, e.g. production of herbicides chloroxuron, 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) and binofex [300]. Because PCDEs have physico-chemical properties like PCBs, they are or were used also as heat exchangers. One product is Dowtherm A, a PCDE - PCB mixture, with heat transfer applications. However, in general their use pattern is unknown [301]. Beside the use as heat-exchange fluids, the lower chlorinated PCDEs have been used as flame retardants. It must be also stated that the PCDEs were never directly produced in large quantities. Nevertheless, these aromatic chlorinated compounds have been identified as widespread environmental contaminants. The widespread appearance of PCDEs in the aquatic and terrestrial environment could be most likely due to their presence as... 

HAs have been issued for bromacil, diuron, and fluometuron no occurrence data are available for tebuthiuron or terbacd (295). Chloroxuron [1982-47-4] fenuronTCA [4482-55-7] andnorea [18530-56-8] also are urea herbicides. 

Miscellaneous urea herbicides (chlorobromuron (3,4(bromo-3-chlorophenyl)-1 -methoxy-1 -methylurea), Chlorotoluron (3(3 chlorotoluyl) dimethyl urea), Diuron (N-(3,4 chlorophenyl) N,N dimethyl urea), Monolinuron (3(4, chlorophenyl-1-methoxy-1 -methylurea), Linuron (3,(3,4 dichlorophenyl)-1 -1 -methoxy-1 -methylurea) Chloroxuron (3, (3,4 dichlorophenyl-1,1 dimethylurea)... 

Fig. 9.11 Typical chromatograms obtained from 5pl injections of soil extracts (a) unfortified and (b) fortified with uron herbicides at 2mg kg-1.1, Monuron 2monoLinuron 3 Metobromuron 4 Chlorotoluron 5 Diuron 6 Linuron 7 Chlorbromuron and 8 Chloroxuron.

Photolytic. The UV irradiation of an aqueous solution containing chloroxuron for 13 h resulted in 90% decomposition of the herbicide. Products identified (% yield) were mono- (2.2%) and didemethylated (4.2%) products and carbon dioxide (64%) (Plimmer, 1970). 

The herbicidal properties of crystalline chloroxuron (12) were described by Aebi and Ebner (1961). It is absorbed by the roots and the leaves and is used for the pre-or postemergence control of annual grass and particularly of broad-leaved weeds. Owing to its poor water solubility and to its strong bonding to soil colloids, it remains near to the soil surface, and in dry weather the area treated must be irrigated to attain adequate herbicidal action. 

Voss and Geissbiihler (1966) compared the translocation of fluometuron, chloroxuron and metobromuron and found a considerable difference in the mobility of the three herbicides. Of the labelled compounds taken up from the nutrient solution through the roots of beans, chloroxuron was absorbed mainly in the roots, only a small quantity entering the stalk. Metobromuron and fluometuron were rapidly translocated into the leaves, but metobromuron accumulated in the leaf veins, while fluometuron accumulated in the spaces between the leaf veins. 

FIGURE 25.10 Capillary GC with fused-silica column coated with CP-Sil 5 (analogous to SE 30 and OV-101) of HFB-anilines obtained after extraction of a pure water sample spiked with 1 fjLg/ parent herbicides, and subsequent hydrolysis and derivatization. Stationary phase CP-Sil 5. Symbol explanation Fm, fluometuron Mo, monuron Ml, monolinuron Mb, metobromuron Ct, chlorotoluron Di, diuron Fi, linuron Mx, metoxuron Cb, chlorbromuron . Cx, chloroxuron Dx, difenoxuron. (From de Kok, A., Roorda, I. M., Frei, R. W., and Brinkman, U. A. Th., Chromatographia, 14, 579, 1981. With permission.)... 

The herbicidal effect of aryl- and hetarylurea, systematically studied starting from first observations in 1946, was improved between 1951 [30] and 1973 [31]. From this chemistry today the compounds chloroxuron (Ciba, 1960), dimefuron (Hoechst, 1969), diuron (Du Pont, 1954), ethidimuron (Bayer, 1973), fenuron (Du Pont, 1957), fluometuron (Ciba, 1960), isoproturon (Hoechst, 1974), linuron (Hoechst, 1960), methabenzthiazuron (Bayer, 1968), metobromuron (Ciba, 1963), metoxuron (Sandoz, 1968), monolinuron (Hoechst, 1958), neburon (Du Pont, 1957), siduron (Du Pont, 1964) and tebuthiuron (Elanco, 1973) are still used. 

Comprehensive reviews by Smith, Cripps and Roberts, and Hassall have covered many of the main classes of herbicides such as the ureas (e.g., diuron, linuron, chlorbromuron, chloroxuron, and chlortoluron), triazines (e.g., atrazine, simazine, trietazine, and prometryn), phenoxyalkanoates (e.g., 2,4-D, MCPA, and mecoprop), phenylcarbamates (e.g., propham and barban), benzoic acids (e.g., dichlobenil, dicamba, and chloramben), and dinitroanilines (e.g., trifluralin, nitralin, and isopropalin). Smith classified the major types of reactions into 12 general classes, 9 of which are biologically mediated and 3 of which can occur as a result of either biochemical or chemical mechanisms. Hill has also devised a scheme of 11 general classes. 

Figure 9.6. Uptake by roots and translocation to shoots of (from left to right) " C-labeled chloroxuron, metobromuron, and iluometuron in French dwarf bean seedlings, grown in nutrient solution containing 2.5 Mg/ml (and equal concentrations of radioactivity) of each herbicide. Plants were kept in herbicide solution for 24 h and then transferred to herbicide-free nutrient solution for an additional 24 h. Top Mounted plants. Bottom Autoradiographs of the same plants. [Voss and Geissbiihler reprinted from P. C. Kearney and D. D. Kaufman (eds.), Herbicides Chemistry, Degradation and Mode of Action, p. 86, by courtesy of Marcel Dekker, Inc.]...

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