Pyridine herbicide

Pyridine herbicides are not strongly sorbed to soils and ate readily leached. The mobiUty of flutoxypyt [69377-81-7] has been found to decrease with increasing incubation time (399) this is attributed to entrapment of the herbicide within the soil organic matter. 

Pyridines and Pyridazinones. Pyridine herbicides arc auxin-type herbicides generally used fur selective control of hroadleaved weeds in cropland, rangelands, and noncroplands. The pyridazinones arc used primarily for ihe... 

The newest class of pyridine herbicides with pre- and post-emergent activity, the pyridinesulfoneamides, is typified by A7-(2-chloro-3-pyridme-sulloiiyl)-A7 -[2-(4-di loro-5,6-dimcthylpyrimidyl] urea. 

Chemical/Pharmaceutical/Other Class Chlorinated amino-pyridine herbicide... 

We have found that several new fluorinated herbicide candidates currently under investigation at Monsanto are very efficient at electron capture and thus are ideally suited for negative ion LC/MS. One such candidate is the pre-emergence herbicide dithiopyr 1 which is illustrated in Figure 1. Dithiopyr is representative of a novel class of fluorinated pyridine herbicides whose metabolism has been studied extensively by negative ion LC/MS. 

Three structurally related pyridine herbicides, clopyralid, fluroxypyr, and triclopyr (Figure 1) were tested for cross-reactivity with the polyclonal and monoclonal anti-picloram antibodies. 

Neither antibody cross-reacted appreciably with the other pyridine herbicides as the I q values In all cases were greater than the highest concentration of herbicide tested (50 000 ng/mL for the polyclonal antibody, 10 000 ng/mL for the monoclonal antibody). 

To further study the utility of 3-tfm-pyridines in agrochemicals, we have focused our research to compounds in which the 3-tfm-pyridine is bonded to the rest of the molecular structure via sulfur. One chemical class investigated was sulfonylurea herbicides, and SL-160, the second 3-tfm-pyridine herbicide developed by ISK, was found (4). SL-160 is different from compounds of Figure 1 in that... 

A new class of fluoroalkyled pyridine herbicides has been synthesized from ethyl 4,4,4-trifluoroacetoacetate. The synthetic route involves formation of dihydropyridine intermediate which upon oxidation or dehydrofluorination produces the desired pyridine compounds. Hydrolysis of the ester groups followed by derivatization of the resulting acids yields a variety of herbicidally active pyridine compounds. 

Besides being useful precursors to pyrroles pyridine-2-ones -4-ones, -4-thiones. and -4-imines 4-alkylidene-dihydropyridines thiophenes 1,2,4-triazoles thiapyrane-2-thiones, isoquinoline-3-ones isoben-zothiophenes and 4-mercaptoimidazolium hydroxide inner salts, mesoionic thiazoles are potentially useful in the construction of molecules with herbicidic (39). central nerve stimulating, and antiinflammatory properties (40,41). Application in dye synthesis has likewise been reported (42). 

Applications. Until recently, haloxydine, a herbicide, was one of the few early examples of crop-protection chemicals containing riag-fluofinated pyridines. Fluroxypyr-(l-methylheptyl) and pyroxofop are new herbicides that are being commercialized (Table 14). 

Bipyridines. Siace the 1960s, the most important commercial agrochemical based on pyridine has been the herbicide paraquat (20) which is made from 4,4 -bipyridine (19). The isomeric herbicide diquat (59) is made by an analogous route, but utilising 2,2 -bipyridine [366-18-7] as a precursor. 

Pyridine is a polar, stable, relatively unreactive liquid (bp 115°C) with a characteristic strong penetrating odor that is unpleasant to most people. It is miscible with both water and organic solvents. Pyridine was first isolated, like pyrrole, from bone pyrolysates. Its name is derived from the Greek for fire (pyr) and the suffix idine used to designate aromatic bases. Pyridine is used as a solvent, in addition to many other uses including products such as pharmaceuticals, vitamins, food flavorings, paints, dyes, rubber products, adhesives, insecticides, and herbicides. Pyridine can also be formed from the breakdown of many natural materials in the environment. 

The photodegradation of the contact herbicide paraquat yielded many degradation products, but the major pathway produced l,2,3,4-tetrahydro-l-ketopyrido[l,2-fl]-5-pyrazinium that was further degraded to pyridine-2-carboxamide and pyridine-2-carboxylate (Figure 1.11) (Smith and Grove 1969). 

Only a few investigations have examined the degradation of halogenated pyridines, some of which are the basis of herbicides ... 

The classical route for producing 2,2 -dipyridyl consists in the dehydrodimerization of pyridine on Raney-Ni using a process developed by the Imperial Chemical Industries [63AHC(2)179 68CI(L)49, 80MI4]. 2,2 -Bipyridyl reacts with ethylene bromide to give l,l -ethylene-2,2 -bipyridylium bromide (diquat). The production of one ton of the diquat (which is widely used as a herbicide) requires 1.2 tons of pyridine [Eq.(17)]. 

An alternative approach was used in the synthesis of the herbicide 530, where the sulfoxide 529 was converted to 530 in a single step by heating with lithium chloride in refluxing pyridine <1997TL4339>. The one-pot transformation involves sigmatropic sulfoxide elimination, lithium chloride-induced demethylation of the carbomethoxy group, decarboxylation, and a final isomerization/aromatization step <1997TL4339>. 

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