Herbicides uracil derivs

Reaction of / fZ-amyl alcohol with urea in the presence of sulfuric acid gives a monoalkylated urea (61,62). Monoalkyl ureas are used to prepare uracil derivatives which are useful as herbicides, fungicides, and plant growth regulators (61). 

Malachite green (0.0...2.0) uracil derivatives, triazine herbicides [163] polar lipids [246, 247] phospholipids [248, 249] fatty acids, fatty aldehydes, phospholipids and glycolipids [250] microbiocidal isothiazolones [251]... 

Herbicidal and chemotherapeutic activity have also been noted in other dihydropyrimidines. Certain 5,5-dihalo-6-methoxydihydropyrimidines, especially the 3-substituted derivatives such as (LXXXIll), are reported to have herbicide activity against many grasses and broad-leaf weeds [645] (herbicidal activity of some corresponding A -substituted uracils has been discussed in the preceding section). The compounds can generally be prepared by halogenation of uracil derivatives in alcohol [646, 647]. 

Uracil derivatives can also function as herbicides by inhibition of the enzyme protoporphyrinogen-IX-oxidase (PRO), which is involved in the biosynthesis of chlorophyll <2006H(68)561>. Commercial examples of such PPO inhibitors include isocil 1104, bromacil 1105, terbacil 1106, flupropacil 1107, lenacil 1108, butafenacil 1109, and benzfendizone 1110 (Figure 9). 

Uracil derivatives Butafenacil (292, Inspire , Rebin ) and Benzfendizone (293) were introduced as herbicides in 1998, whereas their pyridazine-derived analogue Flufenpyr-ethyl (295) - in 2000 [258]. Butafenacil (developed by Syngenta... 

The uracils with herbicidal activity do not necessarily contain 5-halo substituents. 3-Cyclohexyl-5-methyluracil [354] (XLIV), l,3-di-isopropyl-6-methyl-uracil [352] (XLV) and 3-s-butyl-5-thiocyanato-6-methyluracil [353] (XLVI), for example, are cited as having this type of activity. 3-Butyl-6-methyluracil (XLlllc) possesses interesting selective activities. For instance, this pyrimidine kills many annual weed species without damage to peas and peanuts, even when applied at twice the concentration needed to kill the weeds [346]. On the other hand, the related 5-bromo derivatives, such as (XLlIlb), are useful as industrial herbicides where it is desirable to kill all plants [346]. 

The herbicides commonly used as arboricides include members of the triazines, ureas, and uracils, for grass and weed control in nursery and Christmas tree plantings. Other compounds include phosphonate and phosphate derivatives, pyridine-based organic acids of high activity, and organic arsenicals. Such a wide... 

Both underivatised and methylated samples are examined because uracil herbicides give a mixture of products on methylation and should be chromatographed in their underivatised forms, whereas carboxylic acid pesticides, e.g. chlorinated phenoxy acid herbicides, are best examined as methyl derivatives. 

Unsubstituted uracils have no herbicidal activity but certain derivatives substituted in the 3,5,6-positions are active. The most important examples are bromouracil, terbacil, and lenacil. These compounds were introduced by DuPont in 1963. These herbicides are applied to the soil and are used for selective weed control. Bromacil and terbacil are pre- and postemergence herbicides they control a wide spectrum of grass and broadleaf weeds when applied early in the growing season. These compounds must be carried to the roots by soil moisture, where they are absorbed and translocated to the rest of the plant. This family of herbicides is used for asparagus, sugar cane, pineapple, apple, and citrus crops. 

Most of the substituted uracils are total herbicides, but certain recently introduced derivatives have a selective action. 

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