TY - JOUR
T1 - Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole
AU - Kadoya, Warren M.
AU - Sierra-Alvarez, Reyes
AU - Jagadish, Bhumasamudram
AU - Wong, Stanley
AU - Abrell, Leif
AU - Mash, Eugene A.
AU - Field, Jim A.
N1 - Funding Information:
We thank Camila Madeira for her assistance with experiments, Chi Nguyen and Dr. Chao Zeng for their help with the Microtox assay, Dr. Christopher Olivares for his guidance, and Dr. Armando Durazo for his support regarding analytical equipment. NSF ( CBET-1510698 ) funded the research conducted for this study. W. M. Kadoya acknowledges the SMART Scholarship, funded by USD/R&E (The Under Secretary of Defense-Research and Engineering) , National Defense Education Program (NDEP)/BA-1 , Basic Research, for providing financial support (tuition and stipend) for his PhD. SMART did not directly fund this study.. Appendix A
PY - 2019/5
Y1 - 2019/5
N2 - Explosives, pesticides, and pharmaceuticals contain toxic nitroaromatic compounds that may form even more toxic azo compounds if they encounter reducing conditions in the environment. We investigated the mechanism by which 4,4′-dimethoxyazobenzene forms in anaerobic sludge incubations of 4-nitroanisole, an analog for the insensitive munitions compound 2,4-dinitroanisole (DNAN). Because studies have reported the mechanism to involve the coupling of reduced nitroaromatic intermediates, specifically aromatic amines and nitrosoaromatics, by nucleophilic processes, we abiotically paired 10 mM 4-aminoanisole with 2 mM 4-nitrosoanisole in nitrogen-flushed microcosms. However, only 7 μM of 4,4′-dimethoxyazobenzene had formed after 24 h. We identified the major product to be 4-methoxy-4′-nitrosodiphenylamine. Repeating this experiment in phosphate buffer at pH 5.1, 7.1, and 8.6 demonstrated that the formation of this unexpected product is acid catalyzed. We found that 4-methoxy-4′-nitrosodiphenylamine is more toxic than 4,4′-dimethoxyazobenzene to the bioluminescent bacterium Aliivibrio fischeri, with IC50 values of 0.1 μM and 0.5 μM, respectively. Both products are several orders of magnitude more toxic than reduced 4-nitroanisole intermediates 4-aminoanisole and 4-nitrosoanisole, as well as DNAN and its aromatic amine metabolites. Six-fold more 4,4′-dimethoxyazobenzene formed when we incubated 4-nitrosoanisole with ascorbic acid, a reducing agent, than when we incubated 4-nitrosoanisole with 4-aminoanisole in the absence of ascorbic acid. We therefore suspect that 4-hydroxylaminoanisole, the first reduction product of 4-nitrosoanisole, is a better nucleophile than 4-aminoanisole and couples more readily with 4-nitrosoanisole. Slightly basic and reducing conditions can prevent the formation and persistence of toxic coupling products on sites contaminated with nitroaromatics, i.e. DNAN-contaminated firing ranges.
AB - Explosives, pesticides, and pharmaceuticals contain toxic nitroaromatic compounds that may form even more toxic azo compounds if they encounter reducing conditions in the environment. We investigated the mechanism by which 4,4′-dimethoxyazobenzene forms in anaerobic sludge incubations of 4-nitroanisole, an analog for the insensitive munitions compound 2,4-dinitroanisole (DNAN). Because studies have reported the mechanism to involve the coupling of reduced nitroaromatic intermediates, specifically aromatic amines and nitrosoaromatics, by nucleophilic processes, we abiotically paired 10 mM 4-aminoanisole with 2 mM 4-nitrosoanisole in nitrogen-flushed microcosms. However, only 7 μM of 4,4′-dimethoxyazobenzene had formed after 24 h. We identified the major product to be 4-methoxy-4′-nitrosodiphenylamine. Repeating this experiment in phosphate buffer at pH 5.1, 7.1, and 8.6 demonstrated that the formation of this unexpected product is acid catalyzed. We found that 4-methoxy-4′-nitrosodiphenylamine is more toxic than 4,4′-dimethoxyazobenzene to the bioluminescent bacterium Aliivibrio fischeri, with IC50 values of 0.1 μM and 0.5 μM, respectively. Both products are several orders of magnitude more toxic than reduced 4-nitroanisole intermediates 4-aminoanisole and 4-nitrosoanisole, as well as DNAN and its aromatic amine metabolites. Six-fold more 4,4′-dimethoxyazobenzene formed when we incubated 4-nitrosoanisole with ascorbic acid, a reducing agent, than when we incubated 4-nitrosoanisole with 4-aminoanisole in the absence of ascorbic acid. We therefore suspect that 4-hydroxylaminoanisole, the first reduction product of 4-nitrosoanisole, is a better nucleophile than 4-aminoanisole and couples more readily with 4-nitrosoanisole. Slightly basic and reducing conditions can prevent the formation and persistence of toxic coupling products on sites contaminated with nitroaromatics, i.e. DNAN-contaminated firing ranges.
KW - 2,4-Dinitroanisole (DNAN)
KW - Aromatic amines
KW - Azobenzenes
KW - Insensitive munitions compound
KW - Nitroaromatics
KW - Nitrosoaromatics
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U2 - 10.1016/j.chemosphere.2019.01.163
DO - 10.1016/j.chemosphere.2019.01.163
M3 - Article
C2 - 30739063
AN - SCOPUS:85061625374
VL - 222
SP - 789
EP - 796
JO - Chemosphere
JF - Chemosphere
SN - 0045-6535
ER -