MONTMORILLONITE SURFACE-CATALYZED HYDROLYSIS OF FENOXAPROP-ETHYL

The degradation of the herbicide fenoxaprop-ethyl [ethyl -[(6-chloro-2 -benzoxazolyl)oxy]phenoxy]propanoate] on homoionic Fe3+, Al3+, Ca2+, a nd Na+ montmorillonite in aqueous medium was studied. The results show that the hydrolysis of the pesticide may involve two different mechan isms, both depending on the nature of the exchangeable cations. The he rbicide hydrolyzes to 6-chlorobenzoxazolinone and ethyl 2-(4-hydroxyph enoxy)propanoate on Fe3+ and Al3+ clays, whereas the fenoxaprop acid [ 4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid] is the main hy drolysis product on Ca2+ and Na+ clays with minor amounts of 6-chlorob enzoxazolinone and 2-(4-hydroxyphenoxy)propanoic acid. The protonation of the benzoxazole ring nitrogen of the herbicide can be responsible for the cleavage of the ether bridge of fenoxaprop-ethyl in the Fe3+ a nd Al3+ systems. Instead, the hydrolysis of the ester bond appears to be favored by the coordination of the carbonyl oxygen of fenoxaprop-et hyl with the hydrated exchangeable metal ions in the Ca2+ and Na+ syst ems.