Montmorillonite surface-catalyzed hydrolysis of fenoxaprop-ethyl

The degradation of the herbicide fenoxaprop-ethyl [ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoate] on homoionic Fe3+, Al3+, Ca2+, and Na+ montmorillonite in aqueous medium was studied. The results show that the hydrolysis of the pesticide may involve two different mechanisms, both depending on the nature of the exchangeable cations. The herbicide hydrolyzes to 6-chlorobenzoxazolinone and ethyl 2-(4-hydroxyphenoxy)propanoate on Fe3+ and Al3+ clays, whereas the fenoxaprop acid [2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid] is the main hydrolysis product on Ca2+ and Na+ clays with minor amounts of 6-chlorobenzoxazolinone 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+ and Al3+ systems. Instead, the hydrolysis of the ester bond appears to be favored by the coordination of the carbonyl oxygen of fenoxaprop-ethyl with the hydrated exchangeable metal ions in the Ca2+ and Na+ systems.