Abstract
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 IC 50 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.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 789-796 |
| Number of pages | 8 |
| Journal | Chemosphere |
| Volume | 222 |
| DOIs | |
| State | Published - May 1 2019 |
Fingerprint
Keywords
- 2,4-Dinitroanisole (DNAN)
- Aromatic amines
- Azobenzenes
- Insensitive munitions compound
- Nitroaromatics
- Nitrosoaromatics
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry
- Chemistry(all)
- Pollution
- Health, Toxicology and Mutagenesis
Cite this
Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole. / Kadoya, Warren M.; Sierra Alvarez, Maria Reye; Jagadish, Bhumasamudram; Wong, Stanley; Abrell, Leif M; Mash, Eugene A; Field, James A.
In: Chemosphere, Vol. 222, 01.05.2019, p. 789-796.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole
AU - Kadoya, Warren M.
AU - Sierra Alvarez, Maria Reye
AU - Jagadish, Bhumasamudram
AU - Wong, Stanley
AU - Abrell, Leif M
AU - Mash, Eugene A
AU - Field, James A
PY - 2019/5/1
Y1 - 2019/5/1
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 IC 50 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 IC 50 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
UR - http://www.scopus.com/inward/record.url?scp=85061625374&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85061625374&partnerID=8YFLogxK
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 -