Rice herbicides

The ring-chiorinated benzyl chlorides are used ia the preparation of quaternary ammonium salts and as iatermediates for pharmaceuticals and pesticides. p-C. orohen zyl chloride is an iatermediate ia the manufacture of the rice herbicide, Saturn ((S-4-chlorobenzyl)-N,N-diethylthiolcarbamate [28249-77-6] (75). The o- and -chlorobenzal chlorides (l-chloro-2-and 4-dich1 oromethylhenzenes) are starting materials for the manufacture of o- and p- chlo rob enz aldehyde s. 

Development of paddy field rice herbicide Thenylchlor, A-(2,6-dimethyl-phenyl)-A-(3-methoxy-2-thenyl)chloroacetamide 98YGK221. 

Santos TCR, Rocha JC, Barcelo D (2000) Determination of rice herbicides, their transformation products and clolibric acid using on-line solid-phase extraction followed by liquid chromatography with diode array and atmospheric pressure chemical ionization mass spec-trometric detection. J Chromatogr A 879(1) 3-12... 

GraysonBT, Webb JD, Factors offecting the performance and crop phytotoxicity of a new rice herbicide, cinmethylin. 1. Effects of water depth and soil type on the distribution and uptake of anmethylin by transplanted and direct-seeded rice,... 

The rice herbicides cinmethylin (Figure 2.23), mefenacet (Figure 2.24) and daimuron and methyldymron (Figure 2.25) also interfere with meristematic activity in susceptible species. 

Coupe, R.H., E.M. Thurman, and L.R. Zimmerman (1998). Relation of usage to the occurrence of cotton and rice herbicides in three streams of the Mississippi Delta Environ. Sci. Technol., 32 3673-3680. 

As an example, an experimental rice herbicide (ERH-1), 2,2-dimethyl-l-(4mthylthio-5-pyrimidinyljindane, was advanced to phase 2 along with a request for a 3 kg sample. Typically expeditious delivery of the sample was required to meet a rapid development strategy, therefore the s)mthetic route (Scheme 1) developed by the discovery group would be utilized to fulfill the sample requirement The synthetic detail of the chemistry was published in the journal Organic Process Research Development, therefore the chemistry will not be discussed in this transcript... 

T.C.R. Santos, J.C. Rocha, D. Barcelo, Determination of rice herbicides, their transformation products and clofibric acid using on-line SPE-LC with DAD and APCI-MS detection, J. Chromatogr. A, 879 (2000) 3. 

A typical thermospray ionization mass spectrum for a sulfonylurea contains a weak protonated molecular ion and three to four characteristic fragment ions. Figure 2 shows the thermospray positive ion mass spectrum for HARMONY. The spectrum contains a protonated molecular ion at m/z 388, the sulfonamide ammonium adduct ion at m/z 239 and the protonated triazine urea fragment ion at m/z 184. At the same time, Figure 3 shows the positive ion thermospray mass spectrum for LONDAX. It contains the protonated pyrimidine amine at m/z 156, the protonated pyrimidine urea is at m/z 199 and the sulfonamide ammonium adduct ion at m/z 247. LONDAX (bensulfuron methyl) is a sulfonylurea rice herbicide and it elutes between EXPRESS and CLASSIC if we use the LC conditions outlined in Figure 1. HARMONY and LONDAX thermospray spectra were generated with the thermospray vaporizer tip temperature at 150°C and the source block temperature at 320°C. 

Of the registered pesticides in California, we have developed antibody for four the triazine herbicides atrazine and simazine, and the rice herbicides thiobencarb and molinate. Of these, an assay for atrazine has been developed and is now being tested. It is 40% cross-reactive to simazine. Assays for the two rice herbicides are now being developed. 

Modification of the Toxicity of Pesticides with Formulation Additives. Potentially the use of additives to modulate the toxicity of pesticides could lead to a considerable increase in their safety to non-target species, man included. This concept has been well explored and exploited in adding safeners to certain herbicides such as the thiocarbamates. These compounds stimulate defensive metabolic reactions in the crop species but not in weeds This principle has also been applied to vertebrates, but only to a very limited degree. Under some circumstances the thiocarbamate rice herbicide, molinate, may show toxicity to carp in nearby ponds. Based on a knowledge of the safeners that are active in plants, a compound was discovered that, when applied with molinate, acted as an antidote/safener for the carp (20). Little effort, either theoretical or empirical, seems to have gone into developing other such examples. 

Synthesis ofTriazolo[1,5-c]pyriniidme Sulfonamides Leading to the Discovery of Penoxsulam, a New Rice Herbicide... 

Bronze prize 5-(2,6-Difluorobenzyl)oxymefhyl-5-mefhyl-3-(3-methylthiophen-2-yl)-l,2-isoxazoline as a useful rice herbicide by I. T. Hwang et al., KRIGT, Korea. 

Seasonal fish kills in these agricultural dred.ns etre attributed to the rice herbicides. Zhe molinate concentration in the Colusa Basin Dr Lin has approached 350 Ug/L during early June idien herbicide use is heaviest. Fetrther downstream in the Sacramento River, near Sacramento s drinking water treatment facility, concentrations of molinate and thiobencarb have exceeded 20 ug/L... 

Flnlayson, B.J. Lew, T.L. Rice Herbicide Concentrations in Sacramento River and Associated Agricultural Drains. Administrative Report 83-7 California Department of Food and Agriculture Rancho Cordova, CA 1983. 

Orthosulfamuron (IR-5878, CAS-No. 213464-77-8) (Fig. 2.2.6) [47], is a broad-spectrum pre- and postemergent rice herbicide developed by Isagro for the control of annual broadleaf and sedge weeds. There is only limited public knowledge available about this compound but it is assumed to be applied at a use rate of 25-150 g-a.i. ha and could be on the market by 2007. 

In this section we discuss the unusual replacement of the phenyl portion of Protox herbicides with a pyrazole ring to give pyrazogyl (78) [88], a rice herbicide initially discovered by Aventis, now Bayer CropScience. 

As discussed in detail in Chapter 4.2, triketones exert their herbicidal mode of action by inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD) [6]. Triketones are not the only herbicide class that have this mode of action, and it has retrospectively been shown that apparently structurally non-related heterocyclic commercial herbicides such as isoxaflutole (7, BALANCE and MERLIN ), and the rice herbicides pyrazolate (8, SANBIRD ) and benzobicyclon (9, SHOW-ACE ) also cause these bleaching symptoms by the same mode of action. However, a common feature of these herbicides, after metabolic activation to the active metabolites (7 ) [7], (8 ) [8] and (9 ) [9] is the presence of an acidic 1,3-dicarbonyl moiety, which is also present in triketones (Fig. 4.3.2). Triketones and related her-... 

These result in a different environmental behavior and different herbicidal activity [14, 18]. The half-lives in paddy field soil rose from 4 to 15 days for pyrazoxyfen and to 38 days for benzofenap. The application rate of 3 kg ha is as high as for both the other rice herbicides but benzofenap allows a longer weed control of up to 50 days compared with 21-35 days with pyrazoxyfen. Importantly, benzofenap is a more crop selective herbicide. Another advantage of benzofenap over pyrazoxyfen is that it is not temperature-dependent. Even at higher temperatures no phytotoxicity is observed. 

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