Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D235/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, condensed with other rings
  • C07D235/02—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, condensed with other rings condensed with carbocyclic rings or ring systems
  • C07D235/04—Benzimidazoles; Hydrogenated benzimidazoles
  • C07D235/06—Benzimidazoles; Hydrogenated benzimidazoles with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached in position 2
  • C07D235/10—Radicals substituted by halogen atoms or nitro radicals

Definitions

• a method of eliminating weeds from an area infested with weed seeds and growing weeds which comprises contacting said area with an effective amount of a benzimidazole represented by the formula wherein R is a perfluoro C -C alkyl group and R, R, R and R" are the same or different members of the group consisting of hydrogen, halo, nitro, C -C alkyl, C C alkoxy and trifluoromethyl.
• This invention relates to a novel herbicidal process comprising the application to an area infested with weed seeds and which is to be planted to crops, of a herbicidal amount of a benzimidazole represented by the formula:
• Substituted benzimidazoles corresponding to the above formula which are substituted in the benzene ring portion of the molecule are named for convenience according to the numbering system above; that is to say, a single substituent on one of the two carbon atoms adjacent to the benzimidazole ring portion will be called a 4-substituent and a single substituent 5 on one of the two carbon atoms remote from the benzimidazole ring portion will be called a 5-substituent.
• the imidazole ring exists as an equilibrium mixture of two tautomeric forms inasmuch as the hydrogen of the imidazole ring can shift from one of the nitrogens to the other.
• a 4,6-dichlorobenzimidazole can also be named as a 5,7- dichlorobenzimidazole and the compound, as it actually exists, is a mixture of these two tautomers. it should be understood, therefore, that the alternate tautomeric structure is in every instance intended to be disclosed by the naming system used throughout this specification.
• a compound represented by the above structure is applied in a suitable formulation at the rate of from 0 5 to 8 pounds per acre to an area which is to be seeded to a crop plant such as corn, cotton or soybeans, which area contains, in addition, weed seeds belonging to both monocotyledonous and dicotyledonous weed species; i.e., the herbicidal benzimidazole is applied preemergently to both crops and weeds.
• the trifiuoromethylbenzimidazole can be formulated as a wettable powder, as a liquid emulsion, or in solid form as a dispersion on a solid carrier.
• 2,5-bis(trifiuoromethyl)benzimidazole was formulated as a percent wettable powder, the other ingredients of the formulation being kaolin, a surfactant such as the sodium salt of a naphthylenic sulfonic acid, and a dispersant, such as the sodium salt of sulfonated lignin.
• This wettable powder was dissolved in 500 ml. of water, and the resulting solution was placed in the concentrate tank of a logarithmic sprayer.
• a sufficient quantity of 2,5- bis(trifluoromethyl)benzimidazole was used to give an initial application rate of 8 pounds per acre.
• the sprayer was calibrated to deliver spray at the rate of 30 gallons per acre.
• the sprayer was preset so that the dosage rate was halved every 6.6 feet of sprayer travel. Stated another way, the spray was applied in an amount that decreased logarithmically from the initial application rate of 8 pounds (30 gallons) per acre as the sprayer moved forward, the half-dosage distance (the distance at which the rate delivered was one-half that of each of the original rates) being 6.6 feet.
• a 6-f0ot-wide band 19.8 feet long was then sprayed with the herbicidal benzimidazole. In that distance, three half-dosage intervals were obtained, beginning with a dosage rate of 8 pounds of the benzimidazole per acre and ending with a dosage rate of 1 pound per acre.
• column 1 gives the application rate
• column 2 the percent control of grass weeds
• column 3 percent control of pigweed
• column 4 percent control of other susceptible broadleaf weeds, including purslane, lambs-quarter, smartweed and carpetweed
• column 5 the percent of resistant broadleaf weeds, including ragweed, Venice mallow and velvetleaf.
• 5-Fluoro-2-trifluoromethylbenzimidazole acts similarly at an application rate of 4 pounds per acre and 5,6-dichloro-2-trifluoromethylbenzimidazole is similarly effective at an application rate of 2 pounds per acre.
• the herbicidal processes of this invention customarily employ a compound represented by the above formula in the form of a dispersion.
• a dispersion can be applied in liquid form by spraying or in solid form by using a fertilizer applicator or the like.
• Formulations suitable for spraying can be prepared as emulsifiable concentrates or wettable powders.
• Typical useful formulations include the following:
• Liquid Formulation 60 mg. of 5-chloro-2-trifluoromethylbenzimidazole 1.25 ml. of ethanol 12.5 ml. of water 0.0125 ml. of dispersant
• Useful dispersants for the above formulation include a mixture of the calcium salt of benzene dodecylsulfonate and either a polyoxyethylene ether of nonylphenol containing 9 ethylenoxide residues in the polyoxyethylene chain or a polyoxyethylene-sorbitan mono-oleate.
• the compounds represented by the above formula are also useful as all-purpose postemergent herbicides, with many of the compounds showing a marked ability to virtually eliminate weeds and crop plants at application rates varying from 2 to 8 pounds per acre depending upon the particular compounds. Because of the extremely high-postemergent activity of the compounds represented by the above formula and the corresponding lack of herbicidal activity against crop plants preemergent, it is of course possible to employ the compounds in processes which involve applying them preemergent to the crops but postemergent to the weeds. As will be understood by those skilled in the art, however, the opportunities for such selective type of application are strictly limited as compared with applications preemergent to both weeds and crops.
• the compounds utilized in this invention are prepared by the method of Phillips, J. Chem. Soc. 1928, 2,393. According to this procedure, a suitably substituted o-phenylenediamine and an organic acid are condensed in the presence of a strong acid, usually hydrochloric acid, to yield the desired product.
• a strong acid usually hydrochloric acid
• perfluoroacetic acid has an acid strength equivalent to that of a strong mineral acid
• the synthesis of 2- trifluoromethylbenzimidazole and related Z-perfluoroalkylbenzimidazoles represented by the above formula can be accomplished without the addition of a mineral acid.
• a typical preparation follows:
• Example I 5-Chloro-2-trifluoromethylbenzimidazole A mixture was prepared containing 30 ml. of trifluoroacetic acid and 70 ml. of water. 7.1 grams of p-chloro-o-phenylenediamine were added and the resulting mixture was refluxed for about 4 hours. The reaction product, a heavy black oil containing a few crystals, was poured into water and stirred until the oil solidified. The product was dissolved in base at a pH of about l1 and some black insoluble material was filtered therefrom. The pH was then lowered to about 7 at which point 5-chloro-2-trifluoromethylbenzimidazole began to crystallize out of solution.
• Example [I 4-Nitro-2,6-bis( trifl uoromethyl )benzimidazole A solution of 40.5 g. of 2,6-dinitro-4-trifluoromethyl-lchlorobenzene in 300 ml. of benzene was mixed with 250 ml. of 14 N ammonium hydroxide. The reaction mixture was stirred at room temperature for about 1.5 hours, at which point in time another 100 ml. of 14 N ammonium hydroxide were added and the stirring was continued for an additional 2 hours. The organic layer was separated, was washed with water and was dried. Removal of the solvents in vacuo yielded 2,6-dinitro-4-trifluoromethylaniline, which melted at about l42144 C. after recrystallization from a hexane-benzene solvent mixture.
• 4-Nitro-2,6-bis(trifluoromethyl)benzimidazole thus prepared has a surprisingly high activity as a preemergent herbicide.
• the compound in greenhouse tests, has demonstrated an ability to eliminate all seedling grass and broadleaf weed species from flats seeded to such species at application rates as low as 1 pound per acre and against mustard and pigweed at application rates as low as one-fourth to onehalf pound per acre.
• application rates of 2 Other compounds coming within the scope of this invention have been prepared by Smith and Stcinle. J. Am. Chem. Soc, 75, 1,292 (i953), by Belcher, Sykes and Tatlow, J. Chem. $00., 4,l59 (1954), by Fernandez-Bolanos ct al., Chem. 500.,
• Example ill 5 6-Dinitro-2-trifluoromethylbenzimidazole
• a nitrating mixture was prepared by adding 70 ml. of 90 percent nitric acid to 200 ml. of percent fuming sulfuric acid with stirring and cooling. 42.5 grams of S-nitro- 2tritluoromethylbenzimidazole dissolved in a mixture composed of 250 ml. of 18 M sulfuric acid and 50 ml. of 20 percent furning sulfuric acid were added to the nitrating mixture. The nitration reaction temperature was maintained at about 50 C. for about one-half hour, and was then heated to about 145 C. and maintained at that temperature for L5 hours. The reaction mixture was poured onto an excess of ice.
• a precipitate comprising 5,6-dinitro-2-trifluoromethylbenzimidazole prepared in the above reaction, was separated by filtration. Recrystallization of the solid from a methanolwater solvent mixture yielded 5,6-dinitro-2triflu0romethylbenzimidazole melting at 234-237 C.
• Certain other compounds represented by the above formula can be prepared by nitrating a Z-trifluoromethylbenzimidazole prepared by the procedures of example l.
• certain chlorine substituted 2-trifluoromethylbenzimidazoles can be prepared by chlorinating Z-trifluoromethylbenzimidazole or one of its substitution products.
• 4,5,6,7- tetrachloro-2-trifluoromethylbenzimidazole is prepared by chlorinating Z-trifluoromethylbenzimidazole until complete chlorination is achieved. The compound melts at about 269-270 C.
• 4,5-Dichloro-2-trifluoromethylbenzimidazole and 4,6- dichloro-2-t1ifluoromethylbenzimidazole can likewise be prepared by chlorinating 4- or 5-chloro-2-trifluoromethylbenzimidazole.
• electronegative groups are the methylsulfonyl, N-methylsulfonamido, the sulfonamido, the cyano and the like groups.
• a method of eliminating weeds from an area infested with weed seeds and growing weeds which comprises contacting said area with an effective amount of a benzimidazole represented by the formula I l R!!! 11 wherein R is a perfluoro C,C;, alkyl group and R, R", R' and R" are the same or different members of the group consisting of hydrogen, halo, nitro, C,C alkyl, C C; alkoxy and trifluoromethyl.
• herbicidally active compound is 4-nitro-2,6bis(trifluoromethyl)benzimidazole.
• a method to control unwanted plants which comprises bringing into contact with said unwanted plants a herbicidally effective amount of 5-chloro-2-trifluoromethylbenzimidazole.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)
• Plural Heterocyclic Compounds (AREA)

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Citations (4)

• 1966
  • 1966-01-26 US US523016A patent/US3632397A/en not_active Expired - Lifetime
• 1967
  • 1967-01-25 ES ES336063A patent/ES336063A1/es not_active Expired
  • 1967-01-25 DE DE19671670623 patent/DE1670623A1/de active Pending
  • 1967-01-26 GB GB4030/67D patent/GB1179461A/en not_active Expired
  • 1967-01-26 BR BR186535/67A patent/BR6786535D0/pt unknown
  • 1967-01-26 FR FR92654A patent/FR1509499A/fr not_active Expired

Patent Citations (4)

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