Kinetics and mechanism of nitromethane chlorination. A new rate expression

Orvik, Jon A.

doi:10.1021/ja00522a050

Cited by 26 publications

(46 citation statements)

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“…The molar yield of chloropicrin from nitromethane in chlorinated samples from plants A, B, and D ranged from 2 to 40% (Figure S11), which is smaller than that observed previously in DI water, , likely due to scavenging of chlorine by other species present in wastewater. The concentration trends of chloropicrin across the treatment trains generally mirrored the concentration profile of nitromethane prior to chlorination (data from plant D shown in Figure ), and although the yield was not 100%, the trend is consistent with our hypothesis that halonitromethanes as a class of byproducts generally derive from halogenation of nitromethane.…”

Section: Results and Discussionmentioning

confidence: 55%

Formation and Fate of Nitromethane in Ozone-Based Water Reuse Processes

Shi

Plata

Kleimans

et al. 2021

Environ. Sci. Technol.

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Ozonation is widely used in wastewater reclamation treatment trains, either for micropollutant control or as a disinfectant and preoxidant in certain reuse processes. We recently found that ozonation of secondary effluent produces nitromethane, which can be efficiently transformed to genotoxic halonitromethanes by chlorination. In this work, the fate of nitromethane through water reuse treatment trains was characterized by analyzing samples from five reuse operations employing ozone. Nitromethane was poorly (<50%) rejected by reserve osmosis (RO), not removed by, and in some cases, increased by ultraviolet/advanced oxidation processes (UV/AOP). Sufficient nitromethane remained after advanced treatment that when chlorine was added to mimic secondary disinfection, halonitromethane formation was consistently observed. In contrast, biological activated carbon removed most (>75%) nitromethane. Bench-scale experiments were conducted to verify low removal by RO in clean systems and with wastewater effluent and to quantify the kinetics of direct and indirect photolysis of nitromethane in UV/AOP. An explanation for increasing nitromethane concentration during AOP is proposed. These results indicate that nitromethane presents a unique hazard to direct potable reuse systems, due to its ubiquitous formation during wastewater ozonation, poor removal by RO and UV/AOP, and facile conversion into genotoxic halonitromethanes upon chlorine addition.

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Section: Results and Discussionmentioning

confidence: 55%

Formation and Fate of Nitromethane in Ozone-Based Water Reuse Processes

Shi

Plata

Kleimans

et al. 2021

Environ. Sci. Technol.

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“…The maximum formation of nitromethane in water from all three plants ranged from 15 to 35 μg L –1 . Typical chloropicrin formation potential in O 3 /BAC effluent is 6–10 μg L –1 , suggesting that the amount of nitromethane formed is high enough to potentially explain most or all of the halonitromethane formation during subsequent chlorination or chloramination, assuming 50–100% molar yield as observed previously during nitromethane chlorination. , …”

Section: Resultsmentioning

confidence: 71%

“…For water samples A and B, break-point chlorine was achieved, but for water sample C, the dominant chlorine species was monochloramine due to the exceptionally high ammonia concentration (46.2 mg L –1 ) (Table S2). While chlorination of nitromethane is well documented, , the kinetics of nitromethane chloramination are currently unknown. We also directly chlorinated the water sample without prior ozonation and found low but nonzero chloropicrin formation (0.15–2.10 μg L –1 ) without preozonation, possibly due to background nitromethane.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, ozonation of secondary N- methylamines was shown to produce nitromethane, which has been used industrially as the precursor to synthetic chloropicrin . Nitromethane is relatively strong carbon acid (p K a = 10.2) with potential carcinogenicity, and its conjugate base carbanion can be successively chlorinated to form chloropicrin at 100% yield with species-specific rate constant between HOCl and the nitromethyl anion of k = 9500 M –1 s –1 . Thus, we hypothesized that nitromethane may be a singular common intermediate between halonitromethane precursors and halonitromethanes in ozonated wastewater.…”

Section: Introductionmentioning

confidence: 99%

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Transformation of N-Methylamine Drugs during Wastewater Ozonation: Formation of Nitromethane, an Efficient Precursor to Halonitromethanes

Shi

McCurry

2020

Environ. Sci. Technol.

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Potable reuse of wastewater is expanding, and ozonation for water reuse is becoming more common, either as a preoxidant before membranes or as part of ozone/biological activated carbon (O3/BAC) systems. However, previous research has demonstrated that ozone drastically increases the formation potential of genotoxic halonitromethanes (HNMs), including during O3/BAC. Chloropicrin, the most common HNM, is synthesized by chlorinating nitromethane, suggesting that nitromethane may be the immediate precursor of chloropicrin, although nitromethane is unlikely to occur naturally in wastewater. We hypothesized that wastewater ozonation forms nitromethane, which would be the key intermediate toward HNMs. Ozonation of wastewater effluent was shown to form abundant nitromethane, which explained the majority (in one case, all) of subsequent chloropicrin formation. Next, we investigated a suspected category of nitromethane precursor: stimulant drugs, such as ephedrine and methamphetamine, and certain antidepressants. These drugs all feature N-methylamine functional groups, and certain N-alkylamines have been shown to produce primary nitroalkanes upon ozonation. Ozonation of N-methylamine drugs ubiquitously formed nitromethane, typically at >50% yield. Subsequent chlorination converted nitromethane to chloropicrin. The reaction mechanism was investigated to understand the variation in nitromethane yield between different precursors. These results suggest that nitromethane fate during reuse and nitromethane control should be investigated.

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“…x) (6) [AmH'] Data for reaction with n-butylamine are in Table 1. In the absence of added amine salt values of kfaSt, representing reaction at the 3-position to give 4, increase linearly with amine concentration.…”

Section: Kand[am12mentioning

confidence: 99%