Nucleophilic Aromatic Substitution Reactions of Chloroazines with Bisulfide (HS^-) and Polysulfides (S_n^2-)

Abstract

Reactions of bisulfide and polysulfides with chloroazines (important constituents of agrochemicals and textile dyes) were examined in aqueous solution at 25 degrees C. For atrazine, rates are first-order in polysulfide concentration, and polysulfide dianions are the principal reactive nucleophiles; no measurable reaction occurs with HS-. Second-order rate constants for reactions of an array of chloroazines with polysulfides are several orders of magnitude greater than for reactions with HS-. Transformation products indicate the substitution of halogen(s) by sulfur. Ring aza nitrogens substantially enhance reactivity through a combination of inductive and mesomeric effects, and electron-withdrawing or electron-donating substituents markedly enhance or diminish reactivity, respectively. The overall second-order nature of the reaction, the products observed, and reactivity trends are all consistent with a nucleophilic aromatic substitution (S(N)Ar) mechanism. Rate constants for reactions with HS- and Sn2- (n = 2-5) correlate only weakly with lowest unoccupied molecular orbital energies, suggesting that the electrophilicity of a chloroazine is not the sole determinant of its reactivity. When second-order rate constants are extrapolated to HS- and Sn2- concentrations reported in salt marsh pore waters, half-lives of minutes to years are obtained. Polysulfides in particular could play an important role in effecting abiotic transformations of chloroazines in hypoxic marine waters.

Heterogeneous Nucleophilic Transformation of Metolachlor by Bisulfide on Alumina Surface

“…The same products were also obtained in one previous study, which identified the polysulfur-substituted products in the nucleophilic reaction of chloroacetaminlide herbicides with polysulfides (S n 2À ) [13]. The nature of the dechlorinated products substituted by nucleophiles suggests the bimolecular nucleophilic substitution (S N 2) mechanism being mainly responsible for metolachlor transformation by bisulfide [41], and the aluminas acting as the solid-mediator for accelerating the reactions between metolachlor and nucleophiles of bisulfide in the heterogeneous system [42,43].…”

Speciation of Polysulfides and Zerovalent Sulfur in Sulfide-rich Water Wells in Southern and Central Israel

“…Polysulfides play an important role in numerous environmental processes due to their high reductive and nucleophilic reactivity. Among those processes are transition metal complexation and pyrite formation (Rickard 1975;Howarth 1979;Luther 1991;Paquette and Helz 1997;Chadwell et al 1999;Luther and Rickard 2005), thiosulfate production by disproportionation to sulfide and thiosulfate under basic conditions (Bloxam 1895;Giggenbach 1974;Licht and Davis 1997), sulfurization of sedimentary organic matter (Aizenshtat et al 1983;Kohnen et al 1989;Vairavamurthy and Mopper 1989;Vairavamurthy et al 1992;Krein and Aizenshtat 1993;Aizenshtat et al 1995;Amrani and Aizenshtat 2004), volatile sulfur compounds (VSCs) formation (Ginzburg et al 1999;Heitz et al 2000;Franzmann et al 2001;Kamyshny et al 2003), as well as reductive dehalogenation and nucleophilic substitution of organo-halogen pollutants (Roberts et al 1992;Perlinger et al 1996;Miller et al 1998;Lippa and Roberts 2002;Loch et al 2002).…”

The Geochemistry of Pesticides

“…Among the other nucleophiles whose reactions with pesticide compounds may be significant in the hydrologic system, perhaps the most important are reduced sulfur anions (Barbash and Reinhard, 1989a), particularly bisulfide, polysulfides (e.g., Barbash and Reinhard, 1989b;Lippa and Roberts, 2002;Loch et al, 2002;Miah and Jans, 2001;Roberts et al, 1992;Stamper et al, 1997), and thiosulfate (e.g., Ehrenberg et al, 1974;Wang et al, 2000). Reactions with these nucleophiles are often an indirect mechanism of biotransformation, as these and other reduced sulfur anions are derived primarily from biological activity.…”

“…Such calculations have, in turn, been shown to be useful for elucidating the effects of pesticide structure on reactivity (e.g., Katagi, 1992;Lippa and Roberts, 2002).…”

“…In such instances, the pH dependence of the reaction rate will parallel that of the attacking species concentration. For pesticide compounds, this effect has been reported for nucleophilic substitution reactions involving H 3 O þ , OH -(e.g., Mabey and Mill, 1978), and HS - (Haag and Mill, 1988b;Lippa and Roberts, 2002;Roberts et al, 1992), for reduction (Strathmann and Stone, 2002a,b;Wang and Arnold, 2003) or hydrolytic catalysis by divalent metal cations (Huang and Stone, 2000), and for reduction by model compounds employed to mimic the electron-transfer capabilities of hydroquinone moieties found in NOM (Curtis and Reinhard, 1994;Tratnyek and Macalady, 1989). Indeed, the latter observation may explain why the reduction of methyl parathion in anoxic sediments was reported by Wolfe et al (1986) to occur more rapidly under alkaline conditions (8 < pH < 10) than under acidic conditions (2 < pH < 6).…”