A Study on the Stability of α-Cyanobenzyl Ester-type Pyrethroids in Mineral Carriers in the Presence of Malathion

Abstract

The stability of various pyrethroids in mineral carriers was studied in the presence or absence of malathion. All the pyrethroids studied were stable in mineral carriers in the absence of malathion. The pyrethroids having a cyano group in their alcohol moiety were significantly unstable in the presence of malathion, while the pyrethroids having no cyano group in their alcohol moiety were stable even in the presence of malathion. The decomposition seems to be caused by the reaction between the cyano group and some acidic, though unidentified, materials formed by the degradation of malathion in the mineral carriers. The results of mass, iH NMR, and IR spectra suggested that the decomposition product was formed through the conversion of a cyano group to a (methylthio)carbonyl group. Some kinds of alkali or alkaline earth metal salts of weak acids, such as calcium carbonate, calcium acetate, sodium phosphate acted as stabilizers for these pyrethroids in the presence of malathion without having any significant effect on the stability of malathion.