Pyraflufen-ethyl

Pyraflufen-ethyl was primarily developed as a cereal herbicide to control a broad spectrum of broadleaf weeds. Pyraflufen-ethyl applied in early postemergence at 12 g a.i. ha provides excellent control of some important weeds such as Anthemis arvensis, Lamium purpureum and Sinapis arvensis and good suppression of Matricaria chamomilla, Stel-iaria media, Veronica persica and Viola spp. 

Pyraflufen-ethyl is also used as the defoliant for cotton and as a desiccant for potatoes. Pyraflufen-ethyl is a novel inhibitor of protoporphyrinogen IX oxidase. Inhibition of this enzyme in chloroplasts causes accumulation of protoporphyrinogen IX, which results in peroxidation of foliar cell membrane lipids under the light and finally death of cells. 

This herbicidal mode of action of pyraflufen-ethyl is similar to those of other peroxidizing herbicides containing a diphenyl ether moiety. Herbicidal effects of pyraflufen-ethyl are revealed as yellowing and browning in the foliar portion, and then death of the whole plant with leaf burn. 

The major metabolite of pyraflufen-ethyl in plants and soils is E-1 (ester hydrolysate). E-2 (phenol derivative) and E-3 (methylated E-2) are also detected as major metabolites in soils. The target analytes are considered to be pyraflufen-ethyl at least in plant materials, pyraflufen-ethyl, E-1, E-2 and E-3 in soils and pyraflufen-ethyl and E-1 in water samples. 

All of the compounds (pyraflufen-ethyl and its metabolites) are converted to E-2 and quantified as the total toxic residue of pyraflufen-ethyl. The conversion to E-2 is carried out by oxidative decomposition with concentrated sulfuric acid. The reaction mixture is extracted with a solvent and subjected to simple cleanup, followed by GC/NPD analysis. This method is rapid and simple compared with the Multi-residue analytical method , and has wide applicability to different varieties of the samples, such as plant materials, soils and water, with only minor adjustment of the analytical method. 

Mass-selective detector, MSD5973, electron ionization energy 70 eV, ion source temperature 135 °C mjz 412 (pyraflufen-ethyl), 398 (E-15), 326 (E-16) and 340 (E-3)... 

For GC/NPD Peaks of the analytes usually appear at retention times around 11.8, 11.3, 7.2 and 6.5 min for pyraflufen-ethyl, E-15 (E-1), E-16 (E-2) and E-3, respectively. Plot the peak areas against the concentrations of the analytes. 

Calculate the concentrations of analytes (pyraflufen-ethyl, E-1, E-2 and E-3) in plant, soil and water samples (mgkg or igL ) using the following equation ... 

Pyraflufen-ethyl and E-15 (methyl ester of E-1) are easily hydrolyzed to E-1. Careful handling is recommended to prevent the hydrolysis of these analytes. 

Pyraflufen-ethyl (ester type) and E-3 are quantitatively converted to E-2 by the sulfuric acid treatment, but not E-1 (free acid type) therefore, methylation of E-1 to E-15 (ester type) is a necessary step for accurate analysis of total residues. 

Pyraflufen-ethyl (Ecopart ) [114] is a broadleaf weed postemergence herbicide for use in cotton and cereals. Pyraflufen belongs to the family of herbicides that inhibit the Protox enzyme. 

Ethyl 2-chloro-5-(4-chloro-5-difluoromethoxy-l-methylpyrazol-3-yl)-4-fluorophenoxy-acetate as a new cereal herbicide, Pyraflufen-ethyl 03YGK2. 

Fig. 3.7. Chemical structure of fluazolate (17), pyraflufen-ethyl (18), and azafenidin (19).

Also published in 2004 were the synthesis and stmcture-activity of several 2- luoro-4-chloro-5-substituted-phenyl pyrrole Protox herbicides, such as compound 84 [95]. This interesting pyrrole class of chemistry further extends the stmcture-activity of the 2-fluoro-4-chloro-5-substituted-phenylpyrazoles fluazolate (17) and pyraflufen-ethyl (18) discussed in Section 3.2.2 (Fig. 3.22). 

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