Studies on the residue chemistry of some organophosphorus pesticides

Soares, Vera Maria (1987) Studies on the residue chemistry of some organophosphorus pesticides. Doctoral thesis, Polytechnic of North London.


The plan of working has involved synthetic organic chemistry and analytical chemistry related to specific studies on two organophosphorus pesticides, viz. Q, Q-diethyl -(K-ethosycarbonyl-8-methylcarbamoylmethyl) phosphorodithioate (common name mecarbam) and 0, G-diethyl S-chloromethyl phosphorodithioate (common name chlormephos).

The preparation of a full range of possible metabolites and their methylated derivatives was carried out and the compounds were characterised by mass spectrometry, nuclear magnetic resonance (ý'P, 1 C, and 'H), and infrared spectroscopy. The spectroscopic data were discussed in terms of structure.

The compounds have also been studied by both electron impact and fast atom bombardment (FAB) mass spectrometry. In general the FAB spectra gave parent ions stronger than from the electron impact technique. The FAB technique, which has not previously been applied to these types of compounds, also presented additional modes pf fragmentation which are discussed.

Separation of the pesticides and their possible metabolites by gas chromatography has been investigated and the combined technique gc-ms (gas chromatography-mass spectrometry) has also shown it is possible to identify certain components by this method.

Hydrolytic studies have shown that mecarbam at 70°C in 50% ethanol (buffer pH 7.0) has a half-life of approximately 3 hours. Chlormephos is considerably more stable. In the presence of alkali, hydrolysis took place by attack either at phosphorus to give Q, Q-diethyl phosphorothioate or at the carbamoyl carbonyl group to give diethoxyphosphinothioylthioacetic acid. Under similar conditions chlormephos also gave 12, Q-diethyl phosphorothioate and a number of other products resulting from reaction of the 12,0-diethyl phosphorothioate and phosphorodi thi oats anions with a further molecule of chlormephos.

Degradation in the presence of lamb liver homogenate was shown to be rapid for both compounds. Any metabolites formed were too rapidly degraded for detection to be possible.

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