Spectrophotometric investigation of palladium(II)–disulfoton complexes in aqueous ethanolic media

Abstract

The systemic insecticide disulfoton {O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate} forms stable complexes with Pd^II in ethanol. With an excess of disulfoton in solution, Pd^II forms 1 : 1 or 2 : 2 complexes. With an excess of PdCl₂, an equilibrium between 2 : 2 and 3 : 2 complexes is maintained; further addition of PdCl₂ leads to a situation where the 3 : 2 complex prevails. With a large excess of PdCl₂, an additional complex of unknown composition, probably 4 : 2, can be observed. The most characteristic absorption maxima for these complexes are exhibited between 270 and 300 nm. Hence, the spectrophotometric determination of disulfoton with PdCl₂ in ethanolic media is possible. By measuring the absorbance at 278 nm, disulfoton can be determined in the concentration range from 2 to 17 mg l^–1(a correlation coefficient of 0.9958 for nine standard solutions was calculated). As PdCl₂ interferes slightly with disulfoton at this wavelength, the measurement can be performed at 390 nm with lower sensitivity. Further, disulfoton can also be determined in ethyl acetate by shaking an ethyl acetate–disulfoton solution with aqueous PdCl₂, whereby the Pd^II-disulfoton complex is extracted into ethyl acetate. This procedure is sensitive and precise, with an optimum concentration range of disulfoton between 1 and 15 mg l^–1 at 268 nm (r= 0.9999). However, it must be noted that this method is inadequate for residue analysis of disulfoton with regard to the specificity and detection limit.