Abstract

MANZANILLA-CANO, José A.; BARCELO-QUINTAL, Manuel H.; RENDON-OSORIO, Reyna B.  and  FLORES-RODRIGUEZ, Julio. EFFECT OF ZN(II) ON ACID HYDROLYSIS OF METHYLPARATHION. Rev. Int. Contam. Ambient [online]. 2006, vol.22, n.1, pp.21-26. ISSN 0188-4999.

Methylparathion (O,O,-dimethyl O-4 nitrophenylphosphorotioate) kinetic transformation in presence of Zn(II) was studied at pH range from 2 to 7. Between pH 2-5 methylparathion degraded, but at pH 6 and 7 Zn(II) precipitated and the pesticide hydrolysis did not occur. The reaction was first order and the rate constant values were 3.38 x 10-2 h-1 (pH 2), 7.69 x 10-3 h-1 (pH 3), 1.31 x 10-2 h-1 (pH 4) and 1.02 x 10-2 h-1 (pH 5). Paranitrophenol appeared as the only electroactive product at all pH values. It is proposed that the main degradation pathway for methylparathion in acid medium was a hydrolysis reaction of the pesticide catalyzed by Zn(II), via an electrophilic mechanism.

Keywords : methylparathion; Zn(II); hydrolysis; polarography; paranitrophenol.

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