QSAR Study of the Reduction of Nitroaromatics by Fe(II) Species

Abstract

The development of predictive models for the reductive transformation of nitroaromatics requires further clarification of the effect of environmentally relevant variables on reaction kinetics and the identification of readily available molecular descriptors for calculating reactivity. Toward these goals, studies were performed on the reduction of a series of monosubstituted nitrobenzenes in Fe(II)-treated goethite suspensions. The energy of the lowest unoccupied molecular orbital, ELUMO (B3LYP/6-31G*,water), of the nitrobenzenes was capable of explaining 99% of the variability in the rates. Results of experiments in which the surface area loading of ferric oxides was systematically varied indicate that (i) the reactivity of mineral-surface-associated Fe(II), Fe(II)surf, toward the reduction of p-cyanonitrobenzene (CNNB) decreased in the order hematite > goethite > lepidocrocite > ferrihydrite and (ii) the surface density of Fe(II)surf did not play a crucial role in determining the observed reactivity trend. CNNB was reduced in Fe(II)-only control experiments in a pH range of 7.28-7.97 with a pH dependency consistent with the transformation of Fe(II) to Fe(OH)3 or related oxides. The pH dependency of the reduction of CNNB in Fe(II)-treated ferric oxide suspensions (pH 6.1-7.97) could be accounted for by the oxidation of Fe(II)surf, forming an Fe(III) oxide.

Reductive Transformation of 2,4-Dinitrotoluene: Roles of Iron and Natural Organic Matter

“…c k obs for the reduction of 25 lM 2,4-DNT in the presence of 10 mM ascorbic acid by 500 lM Fe(II) (right) and 1.0 g L -1 goethite without acidic pre-equilibration (left) reduce goethite during the pre-equilibration period, resulting in the formation of reactive surface-bound Fe(II) species. Observed rate dependence on goethite loading and preequilibration period is in agreement with a previous investigation on 4-cyanonitrobenzene (E m = -0.34 V (Colon et al 2006b)). When 40 lM 4-cyanonitrobenzene was reacted with 1.0 g L -1 goethite (pre-equilibrated with 1.0 mM ascorbic acid for a week at pH 4.0) at pH 7.0, approximately 250 lM Fe(II) (of which 100 lM was adsorbed on goethite) remained in solution after complete reduction to 4-cyanoaniline (Smolen et al 2003).…”

“…Historically, reduction of nitrobenzenes by Fe(II) has been studied in the presence of mineral surfaces because of the pronounced reactivity of sorbed Fe(II) species [see e.g., (Klausen et al 1995;Colon et al 2006b)]. In the environment, surface-associated Fe(II) will coexist with natural organic matter (NOM).…”

The kinetics and QSAR of abiotic reduction of mononitro aromatic compounds catalyzed by activated carbon

“…Under natural anoxic conditions, the predominant transformation pathway of NACs is via reduction of the nitro groups (Barrows et al, 1996;Wang and Arnold, 2003;Colón et al, 2006). Recently, a number of studies have reported that black carbon (e.g., activated carbon, graphite, soot, and charcoal) can act as effective redox mediators and significantly accelerate the reductive transformation process of NACs in the presence of a reductant (Oh and Chiu, 2009;Yu et al, 2011Yu et al, , 2012Amezquita-Garcia et al, 2013;Fu and Zhu, 2013;Gong et al, 2014;Oh et al, 2013).…”

“…Previous researchers have developed predictive models of the reduction reactivity of NACs for various chemical parameters, including the one-electron reduction potential (E 10 h ), energy of the lowest unoccupied molecular orbital (E LUMO ) and electron affinity (EA) (Dunnivant et al, 1992;Heijman et al, 1995;Rügge et al, 1998;Hofstetter et al, 1999;Wang and Arnold, 2003). Colón et al (2006) obtained linear relationships between the rate constant of the reduction of nitrobenzenes (NBs) and the chemical descriptors, such as, log k NBs ¼ 5:98E 10 h þ 2:14 (R 2 = 0.974), log k NBs ¼ 2:29EA À 3:16 (R 2 = 0.834), and log k NBs ¼ À57:8E LUMOðB3LYP=6 31G Ã ;ÀwaterÞ À 6:26 (R 2 = 0.987). However, these models have been unable to accurately predict or explain the reduction reaction of NACs when taking into account only one chemical parameter, since their reduction potential is closely related to various physicochemical properties.…”

Effects of dissolved organic matter on adsorbed Fe(II) reactivity for the reduction of 2-nitrophenol in TiO2 suspensions

“…Iron is the most abundant transition metal in the Earth's crust, and ferrous ion [Fe(II)] adsorption onto mineral surfaces is an important environmental process (Klupinski et al, 2004;Colón et al, 2006;Li et al, 2009). Mineral-bound Fe(II), one of the most reactive chemical reductants present in natural sediments and aquifers, promotes the reductive transformation of organic chemicals (Rügge et al, 1998;Hakala and Chin, 2010).…”