Herbicides fluorine

Chemicals. Both organic and inorganic fluorine-containing compounds, most of which have highly speciali2ed and valuable properties, are produced from HF. Typically these fluorinated chemicals are relatively complex, sometimes difficult to manufacture, and of high value. These materials include products used as fabric and fiber treatments, herbicide and pharmaceutical intermediates, fluoroelastomers, and fluorinated inert Hquids. Other products include BF, SF, and fluoborates. 

Alkylation. Ben2otrifluoride can also be alkylated, eg, chloromethyl methyl ether—chlorosulfonic acid forms 3-(trifluoromethyl)ben2yl chloride [705-29-3] (303,304), which can also be made from / -xylene by a chlorination—fluorination sequence (305). Exchange cyanation of this product in the presence of phase-transfer catalysts gives 3-(trifluoromethylphenyl)acetonitrile [2338-76-3] (304,305), a key intermediate to the herbicides flurtamone... 

Difluoropyridines. 2,4-Difluoropyridine can be prepared (26% yield) from 2,4-dichloropyridine and potassium fluoride in sulfolane and ethylene glycol initiator (403). The 4-fluorine is preferentially replaced by oxygen nucleophiles to give 2-fluoro-4-hydroxypyridine derivatives for herbicidal apphcations (404). 

Applications of the inhibition of enzymes of the shikimic pathway have given rise to the synthesis of numerous fluorinated derivatives of shikimic acid, especially for applications in crop sciences (bactericides, fungicides, herbicides). " Due to the lack of precise data on the inhibition mechanism, these examples are not considered here. 

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... 

Lactofen [77501-63-4] - [HERBICIDES] (Vol 13) - [FLUORINECOMPOUNDS,ORGANIC - FLUORINATED AROMATIC COMPOUNDS] (Vol 11)... 

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... 

Substitution of the chloro atom by bromine, by fluorine, by nitrilo-, hydrazion-, alkyl-, haloalkyl-, alkoxyalkoxy groups leads very often to remarkable herbicidal but seldom -from the practical point of view - to superior activity. It is thereby obvious to everybody active in this field that the qualification superior activity can never relate to one parameter alone activity against the target organisms is, of course, an absolute prerequisite but this activity can, outside the field of industrial weed control, only be made valuable by a complementary suitable crop selectivity pattern. The following compounds resulting from our project reached the level of practical use ... 

The first significant commercial impact of fluorine in agriculture occurred with the introduction several decades ago of an aromatic trifluoromethyl group in several classes of herbicides, such as dinitroaniline, diphenyl ether, and bleaching herbicides. These early classes of herbicides continue to be used today, though their sales are steadily declining as newer, more effective materials are replacing them. 

Dinitroaniline herbicides. Trifluralin (Treflan ), a 4-trifluoromethyl substituted 2,6-dinitroaniline derivative, was the first main fluorine-containing herbicide to be marketed, with 18,000 tons sold in 1982 in the United States alone [16]. Trifluralin, which was introduced in 1960 by Eli Lilly, is a pre-emergence herbicide used in soybean for the control of a variety of grass and broadleaf weeds [17]. It is prepared from the nitration of 4-chlorobenzotrifluoride, followed by nucleophilic displacement of chlorine with di-n-propyl amine (Fig. 3). Following the success of trifluralin, a number of related A/,A/-dialkyl 4-trifluoromethyl 2,6-dinitroaniline herbicides were later introduced [18]. 

Another example of a trifluoromethyl heteroaryl-containing herbicide is di-thiopyr (Dimension ) [72], Structure-activity studies have demonstrated that a fluorinated alkyl group is required for optimum activity at the 2 and/or 6 positions of the pyridine ring [73], Thiazopyr (Mandate , Visor ), a herbicide related to dithiopyr, was introduced by Monsanto in 1992 and later sold to Rohm and Haas. It is used for the pre-emergence control of annual grass and a few broadleaf weeds in tree fruit, vines, sugar cane, and other crops. 

Several aromatic fluorine-containing herbicides were discussed earlier - diflu-fenican in Section 2.1.1.1 and flufenacet in Section 2.1.2.1-or will be discussed in more detail below - picolinafen and beflubutamid in Section 3.1. Another is fluroxypyr, a postemergence herbicide introduced by Dow AqroSciences in the UK in 1985 [146],... 

Protox herbicides. A number of Protox herbicides share a 2-fluorophenyl group. Initial investigations into an alternative synthesis of 2-fluoro-4-chlorophenyl triazolinones resulted in the very promising use of newer fluorinating reagents. The actual synthesis of carfentrazone-ethyl involved the use of 2-fluoroaniline as the starting material (Fig. 35) [150],... 

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