title: A mechanistic study of methyl parathion hydrolysis by a bifunctional organoclay.
abstract: The mechanism for the hydrolysis of methyl parathion (MP) by a bifunctional quaternary-ammonium based long-chained organclay(LCOC) containing an alkylamine (-CH2CH2-NH2) headgroup was elucidated. The pathway of the catalytic hydrolysis of methyl parathion by the LCOC was defined by following the effect of replacing H20 with D20, by replacing the primary amino headgroup by a tertiary amino group, and by a detailed mathematical analysis of the proposed reaction scheme. A phosphorothioate isomer of MP was formed in the presence of the LCOC as an intermediate reaction product, initially increasing in concentration and then disappearing. The isotope effect was minimal and substituting a tertiary amine in the LCOC increased the rate of MP hydrolysis. A mechanism is proposed in which hydrolysis of MP can proceed via both a direct route (specific base hydrolysis) and through the formation of the isomer which then undergoes specific base hydrolysis more rapidly than the parent MP. The relative importance of each pathway is a function of pH with the direct hydrolysis of MP being predominant at higher pH values (pH > 10) and the isomer intermediate pathway predominating at lower pH values (pH approximately 8-10).
authors.affiliation: Research Laboratory of Water Quality, Ministry of Health, P.O.Box 8255, Tel-Aviv 61080, Israel. , Institute of Soil, Water and Environmental Sciences, The Volcani Center, P.O.Box 6, Bet Dagan, 50250, Israel. haim.ravaha@PHLTA.health.gov.il
authors.forename: Chaim
authors.initials: C
authors.lastname: Rav-Acha
authors.forename: Ludmila
authors.initials: L
authors.lastname: Groisman
authors.forename: Uri
authors.initials: U
authors.lastname: Mingelgrin
authors.forename: Zvi
authors.initials: Z
authors.lastname: Kirson
authors.forename: Yoel
authors.initials: Y
authors.lastname: Sasson
authors.forename: Zev
authors.initials: Z
authors.lastname: Gerstl
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007554:Isotopes / Q000737:chemistry; D008743:Methyl Parathion / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D007554:Isotopes; D000644:Quaternary Ammonium Compounds; D008743:Methyl Parathion; D000077215:Clay