Herbicides urea derivatives

Methabenzthiazuron is a preemergence herbicide, urea derivative and photosynthetic inhibitor that inhibits photosynthetic electron transport at the diuron site . After treatment with this herbicide, the wheat crop showed physiological effects , such as a delayed senescence of leaves, a greening effect and a decrease in carbohydrate content. 

You are concerned about the longevity of the herbicide, linuron, leaching into a river from some neighboring farmland. Given the structure of this urea derivative, you expect it will be biodegraded via a hydrolysis mechanism. You recall a report of a hydrolase enzyme from a common bacterium that exhibits a half-saturation constant, KMM, for linuron of 2 /tM and a maximum degradation rate, Vmax, for linuron of 2500 /nmol kg-1 protein s l. 

H Buser, K Grolimund. Direct determination of A -phenyl urea derivatives in herbicide technical products and formulations, using gas-liquid chromatograpy. J Assoc Off Anal Chem 57 1294-1299, 1974. 

These urea derivatives are a large group of important herbicides. The her-bicidal efficacy of the first described member of this group, diuron, was shown in 1951. 

Many commercial herbicides kill weeds by interfering with the action of photosystem II or photosystem I. Inhibitors of photosystem II block electron flow, whereas inhibitors of photosystem I divert electrons from the terminal part of this photosystem. Photosystem II inhibitors include urea derivatives such as diuron and triazine derivatives such as atrazine. These chemicals bind to the Qg site of the D1 subunit of photosystem II and block the formation of plastoquinol (QH2). 

Thus, the reaction has some value for the synthesis of known ureas derived from methoxymethyl amine such as the herbicide Linuron [see scheme 141] (Ref. 196). 

Linuron, a urea derivative herbicide and androgen receptor antagonist, and butyl benyl phthalate, a plasticizer, are two compounds with very different chemical properties, yet in a laboratory animal study, prenatal exposure to a mixture of these produced dose-additive testosterone and other adverse developmental effects. I66 ... 

Some nitrogenous herbicides are derived from urea, such as diuron, and contain an aromatic ring (phenylurea). The corresponding UV spectrum shows an absorption peak at 250 nm (Fig. 54). 

Several compounds among the benzothiazole derivatives have a fungicidal action, while the urea derivatives reveal an important herbicidal action. 

Urea herbicides form, along with phenoxy derivatives and triazines, the most important agricultural herbicide group. Since their discovery almost thirty years ago several tens of thousands of urea derivatives have been synthesised in research laboratories, and almost all of the major pesticide manufactures have marketed herbicides with a urea derivative as the active substance. 

Most of the urea derivatives are compounds with herbicidal activity, although some of the aliphatic guanidine derivatives have a fungicidal action and some of the aromatic thioureas a rodenticidal action. 

The first compound with significant herbicidal action discovered among aliphatic urea derivatives, N-butyl-N, N -dimethylurea (Searle, 1954) was never put on the market. Others, for example, halo and polyhaloallyl-N,N-dimethyl ureas, also have herbicidal properties, while symmetric tetraalkyl-ureas are inactive. 

Urea herbicides with cycloaliphatic substituents may contain several kinds of cycloalkyl and cycloalkenyl radicals, but only those in which two methyl groups are the substituents on N 1 are of satisfactory activity. A longer alkyl chain reduces herbicidal efficiency, this is also true for aryl urea derivatives. 

Diary] and triaryl or naphthyl carbamates exhibit low herbicidal activity. The substitution of the aryl radical for a heterocyclic radical gives heterocyclic alkyl and dialkyl ureas, of which many examples have been prepared in recent years. The herbicidal activity of urea derivatives containing a heterocyclic radical, such as benzthiazole, thiazole, thiadiazole, oxadiazole and pyridine, is favourable if one or two methyl groups are substituted at the N -nitrogen. The carrier of total or selective action in these derivatives is presumably the heterocyclic part of the molecule. More recently several new groups of compounds have become known, mainly in the patent literature, for which the structure-activity on relationships are still to be elucidated. 

Compared to the respective urea derivatives, thiourea derivatives usually have a weaker herbicidal action. According to our present knowledge, this is attributed to the fact that unlike urea derivatives the thiourea derivatives do not exert their action by the inhibition of photosynthesis, but by another still unknown means. 

It was developed as an experimental herbicide in 1958 by the BASF. Relationships between the structure and biological activity of cycloaliphatic urea derivatives were summarised first by Scheurer and Fischer (1962).Three routes are described in the patent literature for the synthesis of cycluron (Fischer et al 1958 Fischer, 1959 Steinbrunn and Fischer 1959). 

Of all the urea derivatives the herbicide fenuron (5) has the highest solubility in water and is the least adsorbed by the soil. Owing to its good water solubility, it is easily washed into the deeper layers of the soil. Absorbed through the roots it kills deep-rooted grass and broad-leaved weeds. It is also effective for the control of... 

Huryn, D.M. and Okabe, M., AIDS-driven nucleoside chemistry, Chem. Rev. 92 (8), 1745, 1992. Holan, G., Rational design of degradable insecticides. Nature (London) 232 (5313), 644, 1971. Meyer, W., Application EP 92-810027 92-810027 496701, 1992, N-[[2-[[(3-oxetanyl)oxy]carbo-nyl]phenyl]sulfonyl]urea derivs. and N-[[2-[[(3-thietanyl)oxy]carbonyl]phenyl]sulfonyl]urea derivs., methods for their preparation and their use as herbicides. 19920116. 

The Lyonnaise des Eaux in France [4.116] has developed a process for the denitrification of underground waters in order to produce drinking water. This process combines a bioreactor with adsorption by powdered activated carbon, together with a hollow-fiber UF unit. This process allows the elimination of nitrates, nitrites, pesticides, and herbicides (atrazine, diethylatrazine, simazine, metabenzthiazuron, and urea derivatives, etc.) as well as taste and odor compounds. These molecules are frequently present in underground waters in Europe, as a result of past intensive agricultural practices. The UF membrane unit also disinfects the water by removing protozoa, bacteria, and viruses. 

Analysis of Urea Derivative Herbicides in Water and Soil... 

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