Methyl parathion structure

Mathematical models have also predicted a low volatility for methyl parathion (Jury et al. 1983 McLean et al. 1988). One study using a laboratory model designed to mimic conditions at soil pit and evaporation pond disposal sites (Sanders and Seiber 1983) did find a high volatility from the soil pit model (75% of the deposited material), but a low volatility for the evaporation pond model (3. 7% of the deposited material). A study of methyl parathion and the structurally similar compound ethyl parathion, which have similar vapor pressures, foimd that methyl parathion underwent less volatilization than ethyl parathion in a review of the data, the reduced level of volatilization for methyl parathion was determined to be due to its adsorption to the soil phase (Alvarez-Benedi et al. 1999). 

Structures of toxicants that can affect pulse rate. Methyl parathion, a commonly used plant insecticide, can cause bradycardia. Imiprimine hydrochloride, a tricyclic antidepressant, can cause either tachycardia or arrhythmia. 

Structure 4.13 s II /= ch3o — p—0——no2 och3 Methyl Parathion 0,0-Dimethyl 0-/ -nitrophenyl Phosphorothioate... 

Figure 1 Structures of the phosphorothioate insecticides chlorpyrifos and methyl parathion and their corresponding oxygen analogs.

Malathion is a widely used member of a class of pesticides known as organophospate derivatives. It is biodegradable and less toxic (LDg for female rats is 1000 mg/kg) than DDT. Several other organophosphorus compounds are modifications of this basic structure. They include dimethoate (LD = 387 mg/kg), chlorpyrifos (LD q = 95-270 mg/kg), and methyl parathion (LD o = 18 -50 mg/kg). These organophosphates often are used in the treatment of many pests that are found on vegetables, or, in the case of methyl parathion, on cotton plants. 

In contrast to the high toxicity of methyl parathion, malathion shows how differences in structural formula can cause pronounced differences in the properties of organophosphate pesticides. Malathion has two carboxyester linkages, which are hydrolyzable by carboxylase enzymes to relatively nontoxic products as shown by the following reaction ... 

Fig. 8.7 Chemical structure of pesticides (a) parathion (b)phosmet (c) terbufos (d) chlopyrifos (e) azinphos-methyl (f) tribufos (g) bomoxynil (h) dichlorophene (i) pentrachlorophenol...

The metabolic and/or hydrolytic products of parathion encountered as residues in the urine include both diethyl phosphoric acid and diethyl phosphorothioic acid, most probably as their salts (potassium or sodium). Derivatization of these residues with diazomethane would result in the formation of three trialkyl phosphate compounds, namely, 0,0-diethyl O-methyl phosphate (DEMMP), 0,0-diethyl 0-methyl phosphoro-thionate (DEMMTP), and 0,0-diethyl S-methyl phosphorothiolate (DEMMPTh). Earlier (15), it had been shown by combined gas chromatography-mass spectrometry and other analytical data that a later-eluting major product ca. 85%) of the methylation of diethyl phosphorothioic acid formed under the conditions of the analytical method was DEMMPTh, and the minor product formed (ca. 15%) was DEMMTP. Accordingly, all three trialkyl phosphates were observed and confirmed by mass spectrometry in the analysis of the human urine extract. Sufficient internal bond energy differences are associated with the isomeric structures DEMMPTh and DEMMTP that qualitatively and quantitatively dissimilar fragmentation patterns are observed for both isomers as can be seen from the mass spectra of these compounds shown in Figure 4. 

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