Catalytic hydrolysis of quinalphos on homoionic clays

The decomposition of quinalphos, O,O‐diethyl O‐quinoxalin‐2‐yl phosphorothioate, on homoionic Cu(II)‐, Fe(III)‐, Al‐, Na‐, K‐ and Cabentonites in hydroalcoholic solution has been investigated. The results show that the hydrolysis of the pesticide may involve two different mechanisms, both depending on the nature of the exchangeable cations. The pesticide hydrolyses to 2‐hydroxyquinoxaline on the Cu‐, Fe‐ and Al‐clays, whereas O‐ethyl O‐quinoxalin‐2‐yl thiophosphoric acid is the main product of hydrolysis on the Na‐, K‐ and Ca‐clays. The de‐ethylation reaction appears to be favoured by the hydrolysis of the Na‐and K‐clays. A bidentate complex formed by quinalphos and the interlayer exchangeable cations may be responsible for the formation of 2‐hydroxyquinoxaline. The presence of this product in the interlamellar region of clay was shown by infrared and X‐ray data.