Thiadiazole herbicides

Thiadiazole herbicides, e.g., the post-emergence maize-selective herbicide fluthiacet-methyl (119 1999, Action ,... 

Thiosemicarbazides are useful in forming 1,3,4-thiadiazoles, a class of compounds having herbicidal activity. 

Chemists have found numerous industrial applications for 1,2,3-thiadiazole derivatives. In particular, 1,2,3-thiadiazole derivatives have been used as insecticide synergists, herbicides, and polymer compounds. They have also been shown to have sedative, antibacterial, and antibiotic activity. Examples of these compounds were discussed in CHEC(1984) and CHEC-II(1996). 

Thiadiazoles have found applications as pharmaceuticals, fungicides, herbicides, bacteriocides, dyes, lubricant additives, and vulcanization accelerators. Cephalosporins incorporating a 1,2,4-thiadiazole ring into the side chain have good antibiotic and antimicrobial properties. 

Both 3-amino and 5-amino-1,2,4-thiadiazoles form the expected derivatives with isocyanates, carbamates, and chloroformates the products from the reaction with the 5-amino isomer have been claimed as herbicides and bactericides <84CHEC-I(6)463>. 

Investigations on the nature of a colored impurity that occurs during the manufacture of the triazine herbicide metribuzin led to an unusual synthesis of 2,5-dihydrazino-l,3,4-thiadiazole (156). Addition of HjOj to the dihydrazide (155) in aqueous hydrochloric acid, and storage overnight followed by a complex workup, gave (156) in a crude yield of 28% <90JHC1053>. 

Di(halogenoalkenylthio)-l,2,4-thiadiazoles are useful as defoliants, herbicides, insecticides, and rubber preservatives.204... 

The widely used phenylureas have their heterocyclic counterparts, particularly amongst the 1,3,4-thiadiazoles. They are persistent total herbicides and important examples are tebuthiuron (11) (69GEP1912543) and thiazafluron (12) (69GEP1816696). Benzothiazolyl ureas such as methabenzthiazuron (13) (67BRP1085430) and benzthiazuron (60JIC621), which lacks the 1-methyl group, are also herbicidal. 

Flufenacet (Cadou , Drago ), the 5-trifluoromethyl-1,3,4-thiadiazol-2-yloxy acetanilide herbicide developed by Bayer CropScience, belongs to the oxyacet-amide class of herbicides. Flufenacet is effective in controlling a broad spectrum of annual grass, hedges, and small broadleaf weeds [74]. 

Herbicides that act as inhibitory uncouplers are dinitro-phenols, N-phenylcarbamates, acylanilides, halogenated benzoni-triles, substituted imidazoles, substituted benzimidazoles, bromofenoxim, substituted 2,6-dinitroanilines, pyridinols, and substituted 1,2,4-thiadiazoles (2). 

Generic structures (41) and (42) are examples of thiadiazoles with herbicidal activity (75USP3874873, 79GEP2728523). 

During the past 15 years numerous patents have issued on the synthesis and use of 1,2,4-thiadiazoles as fungicides, herbicides, insecticides, bactericides, dyes, lubricant additives and vulcanization accelerators. The largest number of patents appear to be concerned with fungicides. ... 

The well-known herbicide spike is prepared in high yield by heating in toluene a mixture of pivalic acid, JV-methylthiosemicarbazide, sulfuric acid and polyphosphoric acid to give (228 R = H), which on further treatment with methyl isocyanate yields (228 R = CONHMe) (81USP4283543). Other patented processes are known (76GEP2541115). Details on the structure-activity relationship of compounds in this class are available (70MI42700). A thiadiazole-containing insecticide is methidathion (229). 

Trifluoroacetic acid or trifluoroacetic acid anhydride reacts with hydrox-amic acid amides, thiosemicarbazide, and 1,2-diaminopyridine to yield herbicidal active 1,2,4-oxadiazoles [78GEP(0)2801509], fungicidal-active 1,3,4-thiadiazoles (80USP4264616), and 2-trifluoromethyltriazolo[l,5-alpyridines [80JFC(15)179. 2-Trifluoromethyl-L-histidine was obtained from L-histidine on treatment with benzoyl chloride/sodium hydroxide and subsequent ring closure with trifluoroacetic anhydride (78JOC3403) (Scheme 41). 

Dimercapto-l,3,4-thiadiazole has been used as a reagent for photometric determination of metals under the name of Bismuthiol It has also, like several of its S-substituted derivatives, been used as a herbicide. ... 

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. 

Methyl-l-(5-trifluoromethyl-I,3,4-thiadiazol-2-yJ)urea (MC 2692,40), dimethoxyethyl)-l-(5-trifluoromethyl-l,3,4-thiadiazol-2-yl)urea (HCS 3438, 41) and3-(/J, -dimethoxyethyl)-3-methyl-l-(5-<-butyl-l,3,4-thiadiazol-2-yl)urea(HCS 3510,42) are experimental herbicides of this group. This group contains both total and selective herbicides. 

Recently the Velsicol Chemical Co. developed a herbicide containing two five-membered heterocyclic rings, which can be considered a substituted thiadizole or a substituted imidazolidinone. It was introduced under the code number VEL-5026 (Anderson, 1974). Its chemical composition is 3-(5-r-butyl-l,3,4-thiadiazol-2-yl)-4-hydroxy-l-methyl-2-imidazolidone (buthidazole, 6). 

A wide range of 1,2,4-thiadiazoles has been deliberately synthesized in the search for herbicides, and success is frequently claimed in the patent literature. Favorable data are reported for fluorinated structures, e.g., l-(3-trifluoro-methyl-1,2,4-thiadiazol-5-yl)-3,3-dimethyl urea.3 7 3... 

In addition to their important well-established applications as pesticides, herbicides, and azo dyes, described separately in the appropriate Sections (see IV,C IV,E,4 V), 1,2,4-thiadiazoles are of actual or potential value in several technical fields. Derivatives incorporating sulfur-containing functions are especially prominent in this context. 

Aryloxymethyl-5,6-dihydroimidazo[2,l-6][l,3,4]thiadiazol-5-ones (402) have been screened for their herbicidal activity <93MI 805-03>. 

Table 16 [l,2,4]Triazolo[3,4-6][l,3,4]thiadiazoles (170) with fungicidal and herbicidal activities. ... 

Although the 1,2,4-thiazole moiety does not occur in natural products, many synthetic derivatives are biologically active and are used as insecticides, fungicides, herbicides and antibacterials. For instance, 5-ethoxy-3-trichloromethyl-l,2,4-thiadiazole (etridiazole) is used to combat or prevent fungal infestation of plants, fruit, cotton, seeds and soil [149]. 

Approximately half of all commercial herbicides act by inhibiting photosynthesis by interacting with specific sites along the photosynthetic electron transport chain. A number of diverse chemicals including the ureas, amides, triazines, triazinones, uracils, pyridazinones, quinazolines, thiadiazoles, and certain phenols are thought to act specifically at a common inhibitory site at the reducing side of photosystem II (PS II) (U ). 

Continuous study of oxyacetamide chemistry shifted research from the paddy herbicide to an upland herbicide with increasing water solubility that is suitable for such upland use. To this end, benzanellated analogues such as the benzothia-zole moiety of mefenacet were changed to simple five-membered heterocycles that contain at least one nitrogen atom to increase water solubility, and sulfur or oxygen atom to decrease lipophilicity, for instance thiazoles, thiadiazoles, oxazoles and oxadiazoles (Fig. 8.2). Consequently, many patent applications of the new class of heteroxyacetamide herbicides were disclosed [17, 18]. 

Through structure-activity correlation studies with the new oxyacetamide substances, only 1,3,4-thiadiazole derivatives with specified substituents provided high herbicidal activity. Requisite properties of the compound for selection were (1) very good efficacy against grassy weeds, (2) very good compatibility for maize and soybeans, and (3) suitable water solubility (56 mg at 25 °C). Based on these results, flufenacet (FOE 5043 Fig. 8.1) was selected and developed as a second-generation heteroxyacetamide class for use as an upland herbicide. 

Synonyms 1 -(5-t-Butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea Urea, 1-(5-(t-butyl)-1,3,4-triadiazol-2-yl)-1,3-dimethyl-Empirical C9H16N4OS Properties M.w. 228.35 Toxicology LD50 (oral, rat) 644 mg/kg, (oral, mouse) 579 mg/kg poison by ing. TSCA listed Hazardous Decomp. Prods. Very toxic fumes of SOx and NOx Uses Herbicide Regulatory SARA reportable... 

Certain 1,3,4-thiadiazoles, particularly 2-ureido-derivatives, possess herbicidal activity. - l-Methyl-3-(5-t-butyl-l,3,4-thiadiazol-2-yl)urea controls a broad range of weeds when sprayed on the foliage of the seedlings or the surface of the soil at a dosage of 1—2 kg/hm . The 1,3,4-thiadiazole nucleus appears to play an essential part in the activity, since analogous thiazoles are ineffective. The urea derivatives (184) and (185) (previous... 

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