Parathion nitro reduction

Reduction of aromatic nitro groups occurs in three steps, via nitroso and hydroxylamine intermediates, to the amine. The amine can go on to form polymeric residues by a mechanism analogous to that for oxidative coupling of phenols, as in Equation 2. Abiotic nitro reduction is well documented for pesticides that contain aromatic nitro groups, such as the phosphorothioate esters methyl and ethyl parathion (22, 30-33). 

Epoxidation and hydroxylation A-Dealkylation O-Dealkylation -Dealkylation -Oxidation A-Oxidation P-Oxidation Desulfuration Dehalogenation Nitro reduction Azo reduction Cytochrome P450 (CYP) Aflatoxin, aldrin, benzo[a]pyrene, bromobenzene, naphthalene Ethylmorphine, atrazine, dimethylnitrocarbamate, dimethylaniline p-Nitroanisole, chlorfenvinphos, codeine Methylmercaptan Thiobenzamide, phorate, endosulfan, methiocarb, chlorpromazine 2-Acetylaminofluorene Diethylphenylphosphine Parathion, fonofos, carbon disulfide CCLt, CllCb Nitrobenzene O-Aminoazotoluene Flavin-Containing Monooxygenase (FMO)... 

Reduction of Nitro Substituents. These reactions are very common in anaerobic environments and result in amine-substituted pesticides anaerobic bacteria capable of reducing nitrate to ammonia appear to be primarily responsible. All nitro-substituted pesticides appear to be susceptible to this transformation, eg, methyl parathion (7) (eq. 9), triduralin, and pendimethalin. 

For spray residues of parathion Averell and Norris (4) have developed a method that is sensitive to about 20 micrograms. The method is based on the reduction of the nitro... 

The first compound of Equation 36 is not made by the condensation procedure, but by the chemical reduction of a nitro group in parathion. Some compounds are rather difficult to obtain by the general method. However, the next three compounds shown here were prepared by this method. 

A spectrophotometric determination of parathion-methyl (258) in soil and various vegetables is based on reduction of the nitro group to an amino group with zinc/HCl, dia-zotization and coupling with guaiacol (259) to form a yellow-colored azo dye in alkaline medium532. 

Degradation of parathion in soil was by hydrolysis to p-nitro-phenol and diethylthiophosphoric acid and reduction to aminopara-thion (25,26). Chemical oxidation of parathion in soils and waters was not prevalent, although oxidation of the phosphorus-sulfur bond has been shown to occur under ultraviolet light and in oxidizing environments (26). At ordinary levels of application to soil, parathion was degraded within weeks if microbial activity was available (27). Accumulations even after repeated applications were unlikely (28). When higher concentrations were applied to soil, persistence increased. Simulated spills of concentrated parathion resulted in a 15% residue after five years (29) and 0.1% after 16 years (30). 

Reductive reactions, like oxidation, are carried out at different rates by enzyme preparations from different species. Microsomes from mammalian liver are 18 times or more higher in azoreductase activity and more than 20 times higher in nitroreductase activity than those from fish liver. Although relatively inactive in nitroreductase, fish can reduce the nitro group of parathion, suggesting multiple forms of reductase enzymes. 

Because the reduction of aromatic nitro groups is such a facile process, reductive transformation of chemicals containing this moiety is often the dominant pathway for their transformation in the environment. For example, the reduction of methyl parathion, which is representative of the nitro-containing organophosphorus insecticides, to amino methyl parathion has been observed in anaerobic sediments (Wolfe et al., 1986) and flooded soils (Wahid and Sethunathan, 1979 Wahid et al., 1980 Adhya et al., 1981a and 1981b Gambrell et al., 1984), with half-lives on the order of minutes to hours (Equation 3.22). 

This newer analytical approach could effectively replace any need for reductive LCEC in the future, since it appears that most compounds already studied by reductive means can now be done by oxidative HPLC-hv-EC methods as well. This has Included compounds such as 1) organic nltro derivatives, C-nltro, 0-nitro, N-nitro, etc. 2) M-nltroso compounds, such as N-nltrosamlnes, N-nltroso amino acids, etc. 3) organothlophosphates, such as malathlon, parathion, ethion, etc. 4) aromatic esters and amides, such as benzamlde, vitamin B, alkyl benzoates, etc. 5) beta-lactams, such as penicillins and cephalosporins 6) mycotoxlns, such as vomltoxln or deoxynlvalenol ... 

Parathion, paraoxon and EPN are subject to reduction of the aromatic nitro group to an amino group [159] by mammalian, avian and piscine tissues [160], Paraoxon is the most readily reduced of the three compounds, EPN the least. Paraoxon metabolism to aminoparaoxon is the route of inactivation by rat, chicken and guinea-pig livers in vitro [160]. However, enzymatic hydrolysis of the phosphorus-nitrophenyl linkage of the oxo-analogues appears to he a major pathway of detoxication in manunals [142, 161, 162] but bovine rumen fluid is capable of reducing parathion and EPN to their... 

Aliphatic and aromatic nitro compounds are reduced at relatively positive potentials via the hydroxylamines to the corresponding amines. The carcinogenic 4-nitroquinoline-/V-oxide is determined by DPP in the presence of 4-hydroxyam-inoquinoline-/V-oxide and 4-aminoquinoline-/V-oxide via the reduction of the nitro group [79]. Nitrazepam, parathion, nitrofurantoin, and the ni-troimidazoles in blood plasma or urine are also determined via the reduction of the respective nitro groups. 

The few pesticides investigated so far on BDD electrodes using voltammetric methods include some carbamate pesticides (carbaryl, " carbendazim ), and organophosphorus pesticides (parathion, methyl parathion, and fenamiphos ). Determination of the latter group is based on the reduction of the nitro group and thus these pesticides are among the few examples on utilization of BDD electrodes for electroreduction. Carbamate pesticides, the N-substituted esters of carbamic... 

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