Ultraviolet irradiation of fenitrothion and the synthesis of the photolytic oxidation products

Abstract

The ultraviolet irradiation of fenitrothion in oxygenated solutions produced isomerization, oxidation, and solvolysis. In hexane, both the P=S and the aryl methyl group were oxidized to give fenitrooxon and formylfenitrothion. Small amounts of denitrofenitrothion were also formed. Irradiation in methanol gave carbomethoxyfenitrothion formed from oxidation followed by solvolysis. Isomerization of fenitrothion to its S-methyl isomer took place on a small scale in all solvents; however, no S-aryl isomer was detected. Irradiation of hydroxymethylfenitrothion in hexane readily gave formyl-and carboxyfenitrothion. This supports the suggestion that hydroxymethylfenitrothion is a reactive intermediate formed in the photolysis of fenitrothion. Several potential oxidation products, hydroxymethyl, formyl, carboxy, and carbomethoxy analogues of fenitrothion and fenitrooxon were prepared together with the S-aryl isomer. The mass spectral (MS) and nuclear magnetic resonance (NMR) data, gas chromatographic (GC), and thin-layer chromatographic (TLC) properties of these compounds and other fenitrothion derivatives are given.Fenitrothion [O,O-dimethyl 0-(4-nitro-m-tolyl) phosphorothioate] (I) is an important insecticide used in many countries for orchard and field crops. In Canada, its main use is to control defoliators in forests.It is structurally similar to parathion, the ultraviolet (uv) photolysis of which has been extensively studied (Cook and Pugh, 1957; Frawley et al., 1958;Koivistoinen and Merilainen, 1963;El-Rafai and Hopkins, 1966; and Joiner and Baetcke, 1974). In contrast, little work has been carried out on the photolysis of fenitrothion. Brewer et al. (1974) reported the formation of two products on irradiation of fenitrothion with light >300 nm, one of which was identified as 4-nitro-rn-cresol (11). A more exhaustive investigation was carried out by Ohkawa et al. (1974) who studied the photodecomposition in various solvents and as films by both uv and sunlight. Five products were isolated, resulting from photoinduced isomerization, oxidation, hydrolysis, and solvolysis. The predominant reaction in benzene, acetone, methanol, and aqueous methanol was oxidation of the aryl methyl group to give carboxyfenitrothion and its oxygen analogue, which were characterized by nuclear magnetic resonance (NMR) and infrared (ir) spectroscopy.

Photodegradation kinetics of fenitrothion in various aqueous media and its effect on steroid hormones biosynthesis

“…Compound (7), with a molecular weight of 321, was identified as carbomethoxyfenitrothion by its EI spectrum (Greenhalgh and Marshall, 1976;Durand et al, 1994). Besides the typical ions corresponding to the phosphorothioate moiety at m/z values of 125, 79, and 109, the EI spectrum of this compound showed a parent ion at an m/z value of 321 with two characteristic ions at m/z values of 151 and 181 being obtained.…”

“…This compound had been previously identified as one of the fenitrothion photoproducts (Greenhalgh and Marshall, 1976;Durand et al, 1992Durand et al, , 1994; it gives an EI spectrum with characteristic ions at m/z values of 136, 153, and 77.…”

“…Compound (1), with a molecular weight of 277, was identified as fenitrothion, with an OH loss at m/z value of 260 and the characteristic ions of the phosphorothioate moiety at m/z values of 109 and 125 were identified (Greenhalgh and Marshall, 1976;Durand et al, 1992Durand et al, , 1994.…”

“…Besides the typical ions corresponding to the phosphorothioate moiety at m/z values of 125, 79, and 109, the EI spectrum of this compound showed a parent ion at an m/z value of 321 with two characteristic ions at m/z values of 151 and 181 being obtained. The absence of the M-17 (260) ion indicated that a change had occurred in the aryl methyl position (Greenhalgh and Marshall, 1976).…”

“…Therefore, it becomes necessary to monitor the behavior as well as the presence of fenitrothion and its photoproducts in the environment (Lacorte and Barcelo, 1994). In spite of, the many degradation studies carried out using various types of water examining the photolysis and photocatalytic degradation of fenitrothion (Greenhalgh and Marshall, 1976;Mikami et al, 1985;Durand et al, 1992Durand et al, , 1994Kerzhentsev et al, 1996), the concentrations used in many cases were so high (mg/l level) that the behavior of fenitrothion may not adequately reflect what happens in real environmental situations. Furthermore, the differences in direct versus indirect photolysis using nitrate, known to be natural component of environmental water, have not been studied for fenitrothion.…”