Free Radical Chemistry of Disinfection Byproducts. 2. Rate Constants and Degradation Mechanisms of Trichloronitromethane (Chloropicrin)

Abstract

Absolute rate constants for the free-radical-induced degradation of trichloronitromethane (TCNM, chloropicrin) were determined using electron pulse radiolysis and transient absorption spectroscopy. Rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)-, reactions were (4.97 +/- 0.28) x 10(7) M(-1) s(-1) and (2.13 +/- 0.03) x 10(10) M(-1) s(-1), respectively. It appears that the *OH adds to the nitro-group, while the e(aq)- reacts via dissociative electron attachment to give two carbon centered radicals. The mechanisms of these free radical reactions with TCNM were investigated, using 60Co gamma irradiation at various absorbed doses, measuring the disappearance of TCNM and the appearance of the product nitrate and chloride ions. The rate constants and mechanistic data were combined in a kinetic computer model that was used to describe the major free radical pathways for the destruction of TCNM in solution. These data are applicable to other advanced oxidation/reduction processes.

Degradation of nitro-based pharmaceuticals by UV photolysis: Kinetics and simultaneous reduction on halonitromethanes formation potential

“…The first pathway was the homolytic cleavage of CeN bond without deprotonation, which generated the methyl radical and NO 2 radical. Then the intermediate underwent acid-catalyzed hydrolysis to form TBP R1 and TBP N1 and the NO 2 radical was released as NO 2 À (Phillips et al, 2005;Cole et al, 2007 (Fang et al, 2013). Note that the inter-transformation between NO 3 À and NO 2 À may occur during the UV photolysis.…”

Effects of Biochar Amendment on Chloropicrin Adsorption and Degradation in Soil

“…Considerable research has been conducted on the hydroxyl-radical-induced degradation reactions of fumigants [15,34,35]. Mezyk and Cole researched the reaction process and mechanism between CP and free radicals.…”

Free-Radical Chemistry of Disinfection Byproducts. 3. Degradation Mechanisms of Chloronitromethane, Bromonitromethane, and Dichloronitromethane

“…12 Ultimately, the products of these reactions will hydrolyze, to quantitatively produce chloride, carbon dioxide, and nitrite (nitrate). The hydrogen atom reaction for DCNM was also assumed to occur by reductive dissociation, with a model optimized reaction rate constant of 5.0 × 10 8 M -1 s -1 :…”

“…Advantage was taken of the mechanistic insights gained during our previous studies of the radiolytic degradation of chloropicrin. 12 Our previously measured rate constants for the reactions of the HNMs with e aq -and • OH radical, 13 and the results of current byproduct analyses of 60 Co steady-state irradiation experiments, were combined here into a general kinetic computer model to better understand the utility of electron beam irradiation for the treatment of these DBPs in drinking water.…”