Herbicides trifluoromethanesulfonanilide

Although structure-activity studies were carried out on the substituted trifluoromethanesulfonanilides, Trepka and co-workers (5) noted that no single property of the TFMS series members tested could satisfactorily explain their observed herbicidal activity and selectivity toward grasses, broadleaves, and crops. They concluded that a combination of steric, acidic, lipophilic, and electronic properties must govern the pre-and post-emergence herbicidal activity of the TFMS compounds. 

Although the complex herbicidal activity and selectivity characteristics of the trifluoromethanesulfonanilides could not be correlated with single molecular properties of series members, we believed that an appro-... 

The complex activity and selectivity characteristics of substituted trifluoromethanesulfonanilide herbicides were not correctable with single molecular properties (see Table I and Ref. 5). We were particularly interested in determining whether the multiparameter Hansch equation, whose utility and apparent generality has already been substantiated in correlation studies on enzymatic systems (14, 15, 16, 17, 25), drugs and pharmaceuticals (18,19,20,23,24), pesticides (10,21), and plant growth regulators (22), could be used to provide meaningful structure—activity... 

Determination of Octanol/Water Partition Coefficients. Since oc-tanol/water partition coefficient data for trifluoromethanesulfonanilide (I) and its substituted derivatives have not been reported in the literature and since it was not apparent that any of the substituent tt values previously determined by Fujita et al. (11) would be directly applicable to the TFMS herbicidal system, all TFMS partition coefficients and tt values were determined experimentally. The fluoroalkanesulfonanilides are very acidic because of the electron-withdrawing power of the parent fluoro-alkanesulfonyl group (5). The parent TFMS compound (I), for example, has a pKa in water of 4.45 at 25 °C. This inherent acidity extends to all TFMS series members and requires that the usual partition coefficient measurement procedure described by Fujita et al. (11) be modified to obtain accurate values of log P and tt. 

Table V gives substituent tr values measured in the absence of surfactant for the five parent series previously compared in Table III. Examination of the table indicates that the experimentally measured TFMS series tt values do not coincide with those of any of the other parent series but lie roughly midway between the corresponding tt values of the phenoxyacetic acid and phenol series. In those cases where comparisons are possible, ir values for the 4-CH3, 4-F, 4-OCH3, 3-COCH3, and 3-OH substituents in the TFMS series lie closer to the tt values of the corresponding substituents in the phenoxyacetic acid series than they do to those in the phenol series. In contrast, w values for TFMS 4-C1, 3-CF3, 3-C1, and 3-F substituents lie closer to corresponding phenol series tt values. On the basis of the direct comparison between parent series afforded by Table V, it is evident that none of the partitioning data previously presented by Fujita et al. (II) for the various model parent series adequately describe the partitioning behavior of the substituted trifluoromethanesulfonanilide herbicides.

One explanation may be that the substituent is metabolicaUy unstable under the test conditions. An example of this situation can be found in a report by Yapel. In this study of trifluoromethanesulfonanilide herbicides, the sequential removal of substituents from the regression analysis was used as a test of outliers. ... 

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