Insecticides fluorine

Halogen exchange has been the most widely used process for fluorine incorporation at C-3 and C-5 of the pyrazole ring. For instance, bromine-fluorine exchange in the 3-bromopyrazoline 3 was described as an alternative approach for the preparation of the 3-fluoropyrazole derivative 5, a precursor of insecticidal fluorinated anthranilic diamides [2]. Silver fluoride was used as both fluorine source and oxidation reagent of the pyrazoline ring (Scheme 2). 

Clark DA, Lahm GP, Smith BK, Barry JD, Clagg DG (2008) Synthesis of insecticidal fluorinated anthranUic diamides. Bioorg Med Chem 16 3163-3170... 

Rotenoids. The use of rotenone-bearing roots as insecticides in the United States was developed as a result of federal laws against residues of lead, arsenic, and fluorine upon edible produce. Rotenone [83-79-4] (5) is harmless to plants, highly toxic to many insects, and relatively innocuous to... 

Fluorination of hexamethylphosphoramide with ammonium fluoride gives 85-90% yield of the insecticide bis(dimethylamine)fluorophosphine oxide (Dimefox) [5(1] (equation 18). 

Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

The chemistry, insecticidal, activity and toxicity of the major organofluorine insecticides are reviewed. In the ten years since the discovery of DDT opened up a new field of endeavor for the chemist, biologist, and toxicologist, activity in the field of fluorine-containing insecticides has been great. 

The discovery of the phenomenal insecticidal activity of 1,1, l-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT), which occurred less than 10 years ago, opened up a new field of endeavor for the chemist, biologist, and toxicologist. The activity in this field is considerable, and a portion of it has been directed toward efforts-to locate useful insecticides among the fluorine-containing compounds. Some of the fluorine compounds known to be insecticidal were re-evaluated, other compounds were tested biologically for the first time, and new compounds were prepared to be subjected to such tests. 

Tables III to XI have been arranged in an effort to show the comparative activity of the organofluorine insecticides, principally DFDT, against a variety of organisms by including a reference standard compound, usually DDT. It is recognized that it would be advantageous to compare the chlorinated and fluorinated pairs, and this is done in so far as the sketchy data permit.

Monofluoroacetic acid offers little promise as a mosquito larvicide, but 2-ethylhexyl monofluoroacetate is a very powerful aphicide. The high toxicity of the fluorinated lower aliphatic acids and their esters to vertebrates probably precludes their use as insecticides except under highly controlled conditions. The toxicity of the fluorinated acids to the vertebrates is attributed to their interference with an enzyme system, but the possibility of finding one with a high specificity for insects is not excluded. 

The balance of the compounds in Table VIII support the earlier statement that any compound containing fluorine is toxic to moths. These fluorinated hydrocarbons, phenols, acids, sulfonic acids, and sulfones probably act against moths as stomach poisons. The fluorosulfonic acid derivatives and the sulfone with a fluorinated substituent were key compounds whose toxicity to moths laid the groundwork for the deductions which led to the synthesis and testing of DDT as an insecticide. 

The use of plant extracts for insect control dates into antiquity the use of Paris green as an insecticide for control of the Colorado potato beetle in 1867 probably marks the beginning of the modern era of chemical control of injurious insects. The development of lead arsenate followed later in the nineteenth century for gypsy moth control. The commercial production of nicotine insecticides, the production of calcium arsenate at the time of the first world war, and the use of fluorine, arsenical, and cyanide compounds, as well as other inorganic chemicals for insect control, were important steps in pest control. These chemicals were applied largely by dilute high pressure sprays or dusts. 

It is interesting to note that the toxic sodium fluoroacetate (above, p. 11) occurs in the poisonous South African plant gifblaar (Dichapetalum cymosum, PI. I). It has recently been shown that sodium fluoroacetate is a highly effective systemic insecticide, but it is difficult to say exactly how this substance will be applied on a large scale.6 There are many other insecticides containing fluorine and phosphorus, and special precautions must be taken when handling these toxic compounds. 

We concluded that phenoxy, benzyl, benzoyl and phenyl substituents were all members of a congeneric series of substituents to which simpler members, say fluorine or a methyl group also belonged. In other words, for these simple benzyl esters, no bridging atom was required for insecticidal activity. 

Potassium fluoride is a fluorinating agent in organic synthesis. Other applications are in making insecticide formulations, as an additive to flux for making hard solder, and to control fermentation. 

Examples of X groups are fluorine in isoflurophate (Floropryl, no longer available in the United States or Canada) and echothiophate (Phospholine). Parathion and malathion (insecticides) are thiophosphates... 

Pyrethrinoids are powerful natural insecticides that act on the nervous system of insects. They are esters of chrysantemic acid with a substituted cyclopentenol. The replacement of this motif by a more photochemically stable group affords products that are utilizable in agrochemistry. These compounds exhibit a high insecticide activity and are nontoxic for mammals consequently, they are established in very important markets (e.g., deltamethrin, permethriri). Some fluorinated pyrethrinoids have been synthesized and marketed. One goal of these compounds is to enhance the acaricide activity. Some examples are given in Figure 4.46. 

The preparation of new fluorine containing pyridazinones, prepared by electrofluorination in various base. HF systems has been patented by Rikagaku Kenkyusho as a route to herbicidal, insecticidal or bactericidal compounds... 

The interest in fluorinated organic sulphur compounds has continued unabated throughout the current period by virtue of their potential applications in such diverse fields as fuel cells, ion-exchange resins, insecticides, as well as the established surfactants. 

Examples of modem fluorine-containing herbicides, insecticides, and fungicides are shown below Most of these compounds are prepared starting from fluorinated bulk chemicals, such as fluorinated carbocyclic and heterocyclic compounds, benzotnfluonde, fluorinated acetic acid derivatives, and Freons Direct fluonnation is used only occasionally by producers of fine chemicals and will, at least in the near future, remain the domain of producers of bulk chemicals who have the necessary technical expertise... 

The fluorine anaologue of DDT, l,l,l-trichloro-2,2-bis-(4-fluorophenyl)ethane [475-26-3] (DFDT) (mp 44°C), has very similar properties to the chloro compound. It was used as a sanitary insecticide by the German army in World War II, but is too phytotoxic for agricultural use. The rat oral LDBq is 900 mg/kg. 

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