Paraoxon-ethyl

Methyl parathion, fenitrothion, ethyl parathion, fenitrooxon, paraoxon ethyl... 

A multiresidue method for analyzing 28 common organophosphorus pesticides and three of their main metabolites (paraoxon-ethyl, paraoxon-methyl, and malaoxon) in a variety of crop samples has been developed (59). The use of LC-DAD techniques allowed identification of both organophosphorus pesticides and metabolites by means of standard and spectral comparisons, respectively. A typical chromatogram for fortified apple extract is shown in Figure 4. 

Fig. 4 Chromatograms of a blank apple sample (top) and the same apple sample spiked with 27 of the 31 organophosphorus at the following concentration levels (bottom). 1 = paraoxon methyl 500 2 = malaoxon 6400 3 = paraoxon ethyl 800 4 = metidathion 500 5 = azinphos-methyl 200 6 = phosmet 200 7 = parathion methyl 800 8 = malathion 2000 9 = triazophos 200 10 = fenitrothion 800 11= azinphos ethyl 200 12 = chlorfenvinphos 200 13 = quinalphos 200 14 = parathion-ethyl 400 16 = ethrimphos 1000 17 = diazinon 800 18 = coumaphos 800 19 = fonophos 200 21 = phoxim 400 23 = chlorpyriphos-methyl 500 24 = disulfoton 2000 26 = isofenphos 500 27 = fenchlorphos 500 28 = temephos 400 29 = chlorpyriphos ethyl 200 30 = pyrimiphos-ethyl 200 31 = carbophenothion-ethyl 400. The chromatography was carried out with the Altima column using CH3CN/H20 as mobile phase in gradient elution CHjCN from 28 to 39% in 20 min, and then from 39 to 88% in 40 min. (From Ref. 59.)...

Chlorpyrifos, disfulfoion. EPN. fenthion. parathion-ethyl, and parathion-methyl at I jM inhibit nAChRs more potently than I rajWAChE 15 other OP compounds tested (e.g., malaoxon, malathion. Icptophos. and paraoxon-ethyl) are not as potent potency order ford OP compounds tested further against I ACh is disfulfoion (7 (ji.Vf) > parathion-ethyl > parathion methyl > fenthion (75 juA/)- Binding studies indicate that OP rapidly and reversibly bind.s to the receptor followed by stabilisation of the blocked state or receptor dcsensiiizatinn. OP compounds appear to interact directly with 0(4 2 nAChRs. 

Parathion degraded on both glass surfaces and on bean plant leaves. Metabolites reported were paraoxon, 4-nitrophenol, and a compound tentatively identified as 5-ethyl parathion (El-Refai and Hopkins, 1966). Upon exposure to high intensity UV light, parathion was altered to the following photoproducts paraoxon, 0,5-diethyl 0-4-nitrophenyl phosphorothioate, 0,0-diethyl 5-4-nitrophenyl phosphorothioate, 0,0-bis(4-nitrophenyl) 0-ethyl phosphorothioate, 0,0-bis(4-nitrophenyl) 0-ethyl phosphate, 0,0-diethyl 0-phenyl phosphorothioate, and 0,0-diethyl 0-phenyl phosphate (Joiner et al., 1971). 

PB was reacted with the following model compounds paraoxon (diethyl j-nltrophenyl phosphate), EPMP (ethyl Tiiltrophenyl methylphosphonate), PDEP (jg -nltrophenyl dlethylphosphlnate, PNPA ( P7nltrophenyl acetate), and PMP (hydrogen nltrophenyl methylphosphonate). 

The pesticides methyl and ethyl parathion were determined in run-off water er preconcentration on XAD-2. This allowed analyses of these compounds at the parts per billion level (497). Parathion and paraoxon obtained from leaf extracts and orchard soil have also been determined (492). The separation of 30 carbamate pesticides by RPC has been described (493). Various modes of postcolumn fluorometric detection of carbamate insecticides have been reported including post-colun)n reaction between o-phthalaldehyde and methylamine, a carbamate hydrolysis... 

It Is well known that phosphorothlonate insecticides such as parathlon (, 0-diethyl p-nitrophenyl phosphorothloate) and malathion [0, -dimethyl -(l,2 -dlcarbethoxy)ethyl phosphoro-dithioate] are Intrinsically poor inhibitors of acetylcholinesterase and in vivo activation to the respective anticholinesterases paraoxon and malaoxon is required before animals exposed to the phosphorothionates are intoxicated. Since metabolic activation is essential to the biological activity of these thiono sulfur-containing organophosphorus insecticides, compounds of this type may be considered as propesticides or, more specifically, prolnsectlcldes. 

Mevinphos I, dimethoate, mevinphos II, dichlorvos, diazinon, paraoxon, azinphos-methyl, fenamiphos, parathion-methyl, malathion, fenitrothion, azinphos ethyl, fenthion, parathion-ethyl, coumaphos, phorate, phoxim, disulfoton, chlorpyriphos, ome-thoate, monocrotophos, vamidothion, bromophos ethyl, metoxichlor, DDT... 

Water Dimethoate, fenamiphos, bromophos ethyl, fenthion, coumaphos, fenchlorfos, chlorpyriphos, monocrotophos, mevinphos, fosphamidon, paraoxon, azinphos methyl, foxim, carbophenothion, bromophos methyl Carbamates, phenyl urea, anilides, nitrofenoles... 

Isocratic conditions have been established for HPLC with ultraviolet detection to determine trace levels of five pesticides frequently used in fruits, e.g., paraoxon, guthion, methyl-parathion, ethyl-parathion, and fenitrothion, in fruits and surface water (95). And HPLC was adapted for the determination of trace concentrations of seven OPP pesticides in drinking water. The analytes concentrated on the precolumn were eluted and separated on a C18 analytical column with an elution gradient program and determined by measuring their UV absorption (48). 

Figure 8.29 Separation and detection of organophosphate nerve agent compounds (a) 1.0 x 10-5M paraoxon, (b) 1.0 x 10-5M methyl parathion, (c) 2.0 x 10-5M fenitrothion, and (d) 4.0 x 10-5 M ethyl parathion [24].

The methanolyses of several phosphate/phosphonate esters and their thio analogues [e.g. 0,0-diethyl 0-(4-nitrophenyl) phosphate, paraoxon (101 X = O, Z = 4-N02), 0,0-diethyl S- S-dichlorophenyl) phosphorothioate, (102 R = OEt), and 0-ethyl S-OA-dichlorophenyl) methylphosphonothioate (102 R = Me)] catalysed by methoxide and the complex of Zn2+ (MeO-) with 1,5,9-triazacyclododecane (79 M = Zn) were studied in methanol at 25 °C. The reaction of methoxide and (79 M = Zn) with the entire series of esters appears to adhere to a common mechanism that involves pre-equilibrium binding of the substrate, followed by intramolecular attack of the coordinated methoxide concerted with OAr or SAr leaving group departure.79... 

The first of the organophosphorus insecticides to gain widespread use was parathion which is still an important commercial pesticide. This compound (Figure 9) is converted to the S-ethyl isomer by heating whereas paraoxon, a more toxic compound, is formed by enzymic action in plants. In animals, the additional products, p-nitrophenol and p-amino-phenol, are also formed. At present, little information appears to be available regarding the decomposition products of parathion in soils. 

Petroianu, G.A., Kalasz, H. (2007). Comparison of the ability of pyridinium aldoximes to reactivate human RBC cholinesterases inhibited by ethyl- and methyl-paraoxon. Curr. Org. Chem. 11 1624-34. 

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