Sorption in reconstituted waxes of homologous series of alcohol ethoxylates and n‐alkyl esters and their effects on the mobility of 2,4‐dichlorophenoxybutyric acid

Abstract

Equilibrium sorption of n-alkyl esters (dimethyl suberate, diethyl suberate, diethyl sebacate, dibutyl suberate and dibutyl sebacate) and monodisperse alcohol ethoxylates (diethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol and octaethylene glycol monododecyl ether) between the reconstituted cuticular waxes of Stephanotis floribunda Brongn (Madagascar jasmine) or Hordeum vulgare L (barley) leaves and an external aqueous receptor solution was determined. Logarithms of the wax/receptor partition coefficient (K(wax/rec)) of the n-alkyl esters increased linearly with the number of C-atoms. With alcohol ethoxylates, log K(wax/rec) decreased linearly with the number of ethylene oxide units. For both groups of compounds, K(wax/rec) increased with increasing lipophilicity. The values of K(wax/rec) in Stephanotis wax were between 5 and 16 times higher than in barley wax. It is argued that this difference was due to different chemical composition and crystallinity of the waxes. Mobility of [14C]2,4-dichlorophenoxybutyric acid (2,4-DB) in reconstituted Stephanotis and barley wax was increased by a factor of 2-8 by both n-alkyl esters and alcohol ethoxylates. Effects on the mobility of 2,4-DB were linearly related to the internal concentrations of n-alkyl esters and alcohol ethoxylates in reconstituted Stephanotis or barley wax. At the same internal concentrations the effect of n-alkyl esters on the mobility of 2,4-DB in wax exceeded that of alcohol ethoxylates by between 1 and 2 orders of magnitude. Results are discussed in relation to formulating systemic pesticides.