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Title: Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction
Ozone is commonly used as a pre-disinfectant in potable water reuse treatment trains. Nitromethane was recently found as a ubiquitous ozone byproduct in wastewater, and the key intermediate toward chloropicrin during subsequent secondary disinfection of ozonated wastewater effluent with chlorine. However many utilities have switched from free chlorine to chloramines as a secondary disinfectant. The reaction mechanism and kinetics of nitromethane transformation by chloramines, unlike free chlorine, are unknown. In this work, the kinetics, mechanism, and products of nitromethane chloramination were studied. The expected principal product was chloropicrin, because chloramines are commonly assumed to react similarly, although more slowly, compared to free chlorine. Different molar yields of chloropicrin were observed at acidic, neutral, and basic conditions, and surprisingly, transformation products other than chloropicrin were found. Monochloronitromethane and dichloronitromethane were detected at basic pH, and the mass balance was initially poor at neutral pH. Much of the missing mass was later attributed to nitrate formation, from a newly-identified pathway involving monochloramine reacting as a nucleophile rather than halogenating agent, through a presumed SN2 mechanism. The study indicates that nitromethane chloramination, unlike chlorination, is likely to produce a range of products, whose speciation is a function of pH and reaction time.  more » « less
Award ID(s):
2003472 1944810
PAR ID:
10469507
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
American Chemical Society
Date Published:
Journal Name:
Environmental Science & Technology
ISSN:
0013-936X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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