Ozone Promotes Chloropicrin Formation by Oxidizing Amines to Nitro Compounds

Abstract

Chloropicrin formation has been associated with ozonation followed by chlorination, but the reaction pathway and precursors have been poorly characterized. Experiments with methylamine demonstrated that ozonation converts methylamine to nitromethane at ∼100% yield. Subsequent chlorination converts nitromethane to chloropicrin at ∼50% yield under the conditions evaluated. Similarly high yields from other primary amines were limited to those with functional groups on the β-carbon (e.g., the carboxylic acid in glycine) that facilitate carbon-carbon bond cleavage to release nitromethyl anion. Secondary amines featuring these reactive primary amines as functional groups (e.g., secondary N-methylamines) formed chloropicrin at high yields, likely by facile dealkylation to release the primary nitro compound. Chloropicrin yields from tertiary amines were low. Natural water experiments, including derivatization to transform primary and secondary amines to less reactive carbamate functional groups, indicated that primary and secondary amines were the dominant chloropicrin precursors during ozonation/chlorination. Ozonation followed by chlorination of the primary amine side chain of lysine demonstrated low yields (∼0.2%) of chloropicrin, but high yields (∼17%) of dichloronitrolysine, a halonitroalkane structural analogue to chloropicrin. However, chloropicrin yields increased and dichloronitrolysine yields decreased in the absence of hydroxyl radical scavengers, suggesting that future research should characterize the potential occurrence of such halonitroalkane analogues relative to natural radical scavenger (e.g., carbonate) concentrations.

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

“…For precursors containing an amine-group, the combined ultraviolet (UV)/chlorine treatment could oxidize the amine-group to a nitrogroup, which is always a rate-limiting step for the formation of HNMs (Deng et al, 2014). Ozonation also led to a promoted TCNM formation and primary and secondary alkyl amines are the predominant precursors (McCurry et al, 2016). UV irradiation has been recognized as a promising disinfection means because it neither requires additional chemical(s) nor impairs the aesthetic quality (e.g., taste and odor) of treated water and wastewater.…”

Effects of Pre-Oxidation on Haloacetonitrile and Trichloronitromethane Formation during Subsequent Chlorination of Nitrogenous Organic Compounds

“…HANs, including dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), bromochloroacetonitrile (BCAN), and dibromoacetonitrile (DBAN) are often detected in chlorinated water [12]. Trichloronitromethane (TCNM) is the most important HNM that is often identified in chlorinated water [13,14].Nitrogenous organic compounds (NOC) play an important role in providing precursors to generate N-DBPs, such as HANs and HNMs, during chlorination [15,16]. Amino acids (AAs) are the most studied subclass of NOC; they are found widely in fresh waters and are difficult to remove using traditional drinking water treatment processes [17].…”

Reducing disinfection byproduct formation potential using ozonation and biological drinking water treatment

“…For amines ( Figure 6.6c), an ozone adduct on the nitrogen atom leads to formation of N-oxide for tertiary amines and hydroxylamine for primary and secondary amines (von Gunten 2003a) (see also Chapter 4). A recent study also reported formation of nitromethane from ozonation of methylamine (McCurry et al 2016).…”

“…The formation potentials of HAN4 and THAMs decreased 30 to 41% and 20 to 32%, respectively, when the specific ozone dose increased from 0.4 to 1 mg O 3 /mg DOC. Although the differences in concentrations after ozonation did not reach statistical significance (p>0.05), the decreasing trend in formation potentials at higher ozone dose suggests favorable oxidation of HAN4 and THAM precursors to nitroalkane groups which in turn promotes THNM formation (Huang et al 2012, McCurry et al 2016, Yang et al 2012b). These reactions may explain the significant increase in THNM formation potentials from 0.005 to 0.060 µmol/mmol C when ozone dose was increased.…”

“…THMs = trihalomethanes, HAAs = haloacetic acids, CH = chloral hydrate, HK = haloketones, HANs = haloacetonitriles, TCAM = trichloroacetamide, THNM = trihalonitromethanes. Reactions were based on the following references: Deborde and von Gunten (2008), Hubner et al (2015), McCurry et al (2016), Wenk et al (2013), von Gunten (2009), von Sonntag and.…”