| Abstract: | Using a spin-trap reagent 3-nitrosodurene (1,2,4,5-tetramethyl-3-nitrosobenzene), the short-lived free radicals generated by ultraviolet irradiation of fenvalerate (RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] in degassed benzene or dichloromethane, were scavenged as the more stable nitroxide radicals. These radicals were separated by high-performance liquid chromatography and identified individually by electron-spin resonance spectroscopy, as well as by gas chromatography/mass spectrometry. As a result, they were found to be the spin adduct mixtures of the 4-chloro-α-isopropylbenzyl and α-cyano-3-phenoxybenzyl radicals, which are involved in the photo-induced decarboxylation process of fenvalerate. Discrimination of the radicals was also performed by the isotope-labelling method whereby the benzylic proton in the acid moiety was deuteriated. The spin numbers of the nitroxides decreased by about five-fold when photolysis was carried out in oxygenated benzene solution. N-Benzylidene-tert-butylamine N-oxide trapped both radicals but much less efficiently. The nitroxide of the 4-chloro-α-isopropylbenzyl radical was predominant at 25°C or –40°C, but the proportion of the α-cyano-3-phenoxybenzyl nitroxide radical increased at the lower temperature. |
