Chloroacetonitrile and N,2-Dichloroacetamide Formation from the Reaction of Chloroacetaldehyde and Monochloramine in Water

Abstract

Combined chlorine is increasingly being used as an alternative disinfectant to free chlorine to maintain a residual in drinking water distribution systems mainly because it would reduce the formation of regulated disinfection byproducts (DBPs) trihalomethanes and haloacetic acids. However, the use of combined chlorine could promote the formation of currently unregulated nitrogenous DBPs (N-DBPs) such as haloacetonitriles and haloacetamides that are found to be more cyto- and genotoxic than regulated DBPs. Monochloramine quickly reacts with chloroacetaldehyde, a DBP formed during primary disinfection with free chlorine, forming and reaching pseudoequilibrium (equilibrium constant K1 = 1.87 × 10(3) M(-1)) with the carbinolamine 2-chloro-1-(chloroamino)ethanol. 2-Chloro-1-(chloroamino)ethanol undergoes slow dehydration to form the imine 1-chloro-2-(chloroimino)ethane that decomposes at a faster rate to chloroacetonitrile. 2-Chloro-1-(chloroamino)ethanol is also oxidized by monochloramine to produce the previously unreported DBP N,2-dichloroacetamide. The carbinolamine dehydration step was found to be acid/base catalyzed (k2(0) = 3.30 × 10(-6) s(-1), k2(H) = 2.43 M(-1) s(-1), k2(OH) = 3.90 M(-1) s(-1)). In contrast, N,2-dichloroacetamide formation was observed to be only base catalyzed (k3(OH) = 3.03 × 10(4) M(-2) s(-1)). N,2-dichloroacetamide cytotoxicity (LC50 = 2.56 × 10(-4) M) was found to be slightly lower compared to that reported for chloroacetamide but higher than those of di- and trichloroacetamide.

The formation of haloacetamides, as an emerging class of N-DBPs, from chlor(am)ination of algal organic matter extracted from Microcystis aeruginosa, Scenedesmus quadricauda and Nitzschia palea

“…15 Solutions contained AOMs that were chlorinated or chloraminated in sealed 50 mL amber glass bottles at ambient temperature in the dark for a pre-determined time (24 h or 72 h). 18,19 Although many studies have focused on DCAcAm and BAcAm at relatively higher concentrations, 20,21 no studies have reported the reliability of the analytic method used in this study. 16 Ascorbic acid at a concentration of 40 mg L À1 was used to quench residual chlorine and monochloramine before DBPs analysis.…”

The formation of haloacetamides and other disinfection by-products from non-nitrogenous low-molecular weight organic acids during chloramination

“…Other selected LMWOAs (the four saturated carboxylic acids and one aromatic acid) formed more TCM than DCAA during chloramination, indicating the molecular characteristics of LMWOAs impacted the formation of TCM and DCAA. [18,20,21]. It is known that DCAN and TCAN can hydrolyze to form DCAcAm and TCAcAm respectively, which can themselves further hydrolyze to form DCAA and TCAA, respectively ( Figure S2) [44].…”

“…Nonetheless, recent studies have reported that chloramines may provide the nitrogen in HANs and HNMs, during reactions with organic nitrogen precursors [18,19]. And, it was found that non-nitrogenous lignin phenols and chloroacetaldehyde could react with chloramines to form dichloroacetonitrile (DCAN) and chloroacetonitrile, respectively [20,21]. However, knowledge gaps remain regarding whether chloramine may also contribute the nitrogen in HAcAms, and more broadly whether chloramine can also react with non-nitrogenous precursors to produce nitrogenous HAcAms.…”

Occurrence and Comparative Toxicity of Haloacetaldehyde Disinfection Byproducts in Drinking Water

“…Trihalomethanes (THMs) were discovered as the first chemical class of DBPs in 1974. 2 Since then, research has led to the identification of emerging DBPs 3–7 and determination of their formation kinetics, 8–10 toxicity, 7,11,12 exposure, and risk assessment. 13–17 To date, more than 600 DBPs have been identified, and many are reported to be cytotoxic, genotoxic, teratogenic, or carcinogenic.…”