Correlation analyses for bimolecular nucleophilic substitution reactions of chloroacetanilide herbicides and their structural analogs with environmentally relevant nucleophiles.
Second-order rate constants (kNuc) for aqueous-phase bimolecular nucleophilic substitution (SN2) reactions of a range of anionic nucleophiles with alachlor, propachlor, and two analogs of propachlor (a thioacetanilide and a beta-anilide) were fit to the Swain-Scott and Edwards models. Correlations of literature kNuc values for analogous reactions of methyl chloride and methyl benzenesulfonate were included for comparison. The Swain-Scott correlation yielded poor to fair results for chloroacetanilides and their analogs, with adjusted (adj) r2 values ranging from 0.67 to 0.89, which are comparable to correlations for CH3Cl and CH3OSO2Ph (r2 (adj) = 0.80 and 0.85, respectively). Both the one- and two-parameter Edwards models yielded improved correlations for the majority of substrates. A pronounced dependence on the substrate polarizability (alpha) factor generally was observed for the Edwards model, with a negligible dependence on the substrate basicity (beta) factor. Substrate polarizability factors for the one-parameter Edwards model were significantly larger for alachlor, propachlor, and the beta-anilide analog of propachlor than for methyl chloride and methyl benzenesulfonate. This indicates that the chloroacetanilides are activated toward SN2 reactions with highly reactive nucleophiles (e.g., HS-, PhS-, and Sn(2-)) relative to other saturated carbon substrates. At best, the Swain-Scott and Edwards models only furnish order-of-magnitude predictions of kNuc for the substrates investigated.
Lippa
Katrice A
KA
Department of Geography and Environmental Engineering, 313 Ames Hall, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218-2686, USA.
Roberts
A Lynn
AL
D000081:Acetamides / Q000737:chemistry*; D000083:Acetanilides / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D021281:Quantitative Structure-Activity Relationship
D000081:Acetamides; D000083:Acetanilides; D006540:Herbicides; C011088:propachlor; C078188:2-chloro-N-(ethoxymethyl)-N-(2-methyl-6-(trifluoromethyl)phenyl)acetamide