CONVERSION METHOD OF A STARTING MIXTURE OF ISOMERIC PYRETHROIDS SUCH AS CYPERMETHRINE AND CYPHLATRINE CONTAINING LESS PESTICIDALLY ACTIVE ISOMERS TO PESTICIDALLY MORE ACTIVE ISOMERS

摘要

Crystallizable pyrethroid isomer or enantiomer pairs are converted to more pesticidally active isomers by contacting a hydrocarbon slurry of the starting isomers with a base and a catalyst, the catalyst being substantially soluble in the slurry and selected from a quaternary ammonium compound, a quaternary phosphonium compound and a crown ether, agitating the slurry while maintaining a temperature effective for conversion, and recovering the resulting isomers. The tendency to form benzoin ester by-product is reduced by including in the slurry a weak base, an aldehyde scavenger such as a metabisulfite, and/or a tetraalkyl(C1-C5)ammonium halide catalyst dissolved in an aprotic solvent such as an organic nitrile. The process typically is effective for enriching cypermethrin, cyfluthrin and (cyano)(3-phenoxyphenyl)methyl 3-(2,2-dibromoethenyl)-2,2-dimethylcyclopropanecarboxylate in the more active species.