DETERMINATION OF (R)-EPIMERS AND (S)-EPIMERS AT C-1 IN RESIDUAL AMOUNTS OF (+/-)-CIS,TRANS-PERMETHRIN AND CYPERMETHRIN BY GAS-LIQUID-CHROMATOGRAPHY

Treatment of (1R)cis-, (1S)trans- and (1R)trans-permethrin with sodium l-menthylate at room temperature produced the l-methyl esters of the corresponding 2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylic acids without epimerization at C-1 or C-3. These three esters, or the mixture of four esters produced by similar treatment of (±)-cis,trans-permethrin were readily separated by gas-liquid chromatography on OV-210. Minimum detectable amounts of each ester were ca. 0.1 ng using a pulsed 63Ni electron-capture detector. The l-menthyl esters corresponding to the permethrin isomers could also be prepared in high yield and without epimerization by alkaline hydrolysis at room temperature to the respective cyclopropanecarboxylic acids, crown-ether-catalyzed conversion to the benzyl esters and subsequent room-temperature trans-esterification of this ester with sodium l-menthylate. Using the longer procedure, cypermethrin could be converted into the same four-component mixture of l-menthyl esters that was obtain from permethrin. The application of these procedures to the determination of the individual (R)- and (S)-epimers (at C-1) in residual amounts of the parent pyrethroids is discussed. © 1979.