Quantitative determination of the enantiomeric purity of synthetic pyrethroids. Part II. S-bioallethrin

Abstract

S-Bioallethrin consists primarily of (+)-allethronyl-(+)-trans-chrysanthemate, but technical samples contain small amounts of other allethrin isomers. The ratio of diastereoisomers can be measured directly from the nuclear magnetic resonance spectrum after using a europium shift reagent, when many of the resonances split into two distinct diastereoisomer signals. If the enantiomeric purity of the chrysanthemate moiety is determined independently, then the absolute enantiomeric purity of the allethrin sample can be calculated. Standard deviations for the measurement of laboratory or technical samples were between 0·3 and 0·7 per cent.

The accuracy of the method was verified by independently determining the enantiomer ratios of various allethrolone samples by gas chromatography of their diastereoisomeric (–)-α-methoxy-α-trifluoromethylphenylacetic esters, esterifying with natural (+)-trans-chrysanthemic acid and redetermining the enantiomeric purity by nuclear magnetic resonance. Good agreement was achieved between the two determinations.

The nuclear magnetic resonance method should also be suitable for measuring the diastereoisomer ratio of cis-allethrins.