Sorption and catalytic hydrolysis of diethatyl-ethyl on homoionic clays

Sorption and catalytic hydrolysis of the herbicide diethatyl-ethyl [N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester] on homoionic Na+-, K+-, Ca2+, and Mg;(2+)-montmorillonite clays were studied in aqueous media. The Freundlich sorption coefficient, K-f, measured from isotherms on clay followed the order of Na+ approximate to K+ > Mg2+ approximate to Ca2+. Analysis of FT-IR spectra of diethatyl-ethyl sorbed on clay suggests probable bonding at the carboxyl and amide carbonyl groups of the herbicide. The rate of herbicide hydrolysis in homoionic clay suspensions followed the same order as that for sorption, indicating that sorption may have preceded and thus caused hydrolysis. Preliminary product identification showed that hydrolysis occurred via nucleophilic substitution at the carboxyl carbon, causing cleavage of the ester bond and formation of diethatyl and its dechlorinated derivative, and at the amide carbon, yielding an ethyl ester derivative and its acid. These pathways also suggest that hydrolysis of diethatyl-ethyl was catalyzed by sorption on the clay surface.