On the possibility of evaluative prediction of the extraction of organic substances of complex structure using the method of group increments

Abstract

The distribution of pesticides of different classes (amides, anilinopyrimidines, benzene derivatives, benzoylphenylureas, benzenesulfonates, hydrazides, dinitroanilines, carbamates, pyretroids, pyrimidines, tetrazines, triazoles, pheny lureas, organophosphorus compounds, esters of carboxylic acids) was studied at 20 ± 1 °C in the extraction systems of hexane–water, hexane–acetonitrile, hexane– acetonitrile and water mixture that are most often used in analytical chemistry of pesticides. The distribution constants P of pesticides and the increments of logarithms of the distribution constants If of their functional groups between the hydrocarbon and polar phases are calculated. Two main methods for evaluative prediction of lg P of pesticides are proposed and approved – substitutive method based on the calculation of lg P by replacing the substituents in the base molecule and the method of absolute addition of increments. The possibilities of the both methods are illustrated. The reasons for the deviations of the experimental values from the calculated ones are discussed. The influence of the nature and composition of the polar phase on the magnitudes of the observed deviations is estimated. In particular, they decrease dramatically with an increase in the acetonitrile content in the polar phase. Averaged values of correction to the calculated values of lg P are introduced. In most cases, they allow predicting lg P of pesticides with a deviation of not more than 0.5–1.0 from the calculated one.