Mercury-Promoted Hydrolysis of Parathion-methyl:  Effect of Chloride and Hydrated Species

Abstract

Mercury salts are commonly used in laboratory and field experiments as biocides. It has been previously reported that Hg(II) can enhance chemical hydrolysis of a number of pesticides. Earlier studies on metal-promoted hydrolysis have reported overall rate constants as a function of total metal concentration. There are three advantages in reporting the relative importance of the different species: (1) results can be extrapolated form one situation to another, (2) rates can be predicted for specific conditions, and (3) greater understanding of the catalysis mechanism can be gained. In this study, mercury-promoted hydrolysis of parathion-methyl (O,O-dimethyl-O-p-nitrophenyl phosphorothionate), a probe organophosphate compound (OP), was studied as a function of Hg(II) speciation. The observed rate of hydrolysis was a function of specific mercury species rather than of the total mercury in solution. Second-order rate constants were determined experimentally at various pH values. A pH-dependent kinetic expression, k obs = (αHg 2+ k 1 + αHgOH + k 2 + αHg(OH) 2 k 3) where ki = with Ki representing the Hg:OP equilibrium constant, the rate constant for Hg:OP hydrolysis for the different Hg(II) species, and α is the fraction of the total Hg(II) present as specific species, provides a plausible interpretation for the system. Mercury-chloride species proved to have little catalytic power, whereas the contributions for Hg2+ and Hg(OH)+ were significant. Our results also suggest that a mixed mechanism (electrophilic and nucleophilic) may have to be considered for general metal-promoted hydrolysis of OPs.

Photocatalytic degradation of methylparathion—An endocrine disruptor by Bi3+-doped TiO2

“…These include the use of UV radiation and hydrogen peroxide [3,4], ultrasonic irradiation [5], or mercury promoted hydrolysis [6]. The major disadvantage of these technologies is that they are designed for decontamination of aqueous solutions with very low active ingredient contents and are not suitable for degrading higher concentrations of unwanted pesticides.…”

31P NMR and ESI-MS Study of Fenitrothion-Copper Ion Complex: Experimental and Theoretical Study

“…The transition Cu 2+ metal was chosen because of their possible interaction with sulfur containing ligand in solution. The Cu 2+ ion has strong affinity to S atom 21 in the compounds on the basis of HSAB theory. 21 The ESI-MS and MS/MS data for the FN in methanol and FN with copper ions in 50% DDW-50% Methanol are summarized in Table 3.…”

“…The Cu 2+ ion has strong affinity to S atom 21 in the compounds on the basis of HSAB theory. 21 The ESI-MS and MS/MS data for the FN in methanol and FN with copper ions in 50% DDW-50% Methanol are summarized in Table 3. Protonated molecular ion peak at 278 (m/z) was attributed to [ Figure 3, excellent agreement is observed between the theoretical and experimental spectrum.…”

Electrochemical treatment of drainage water from toxic dump of pesticides and degradation products

“…Various innovative technologies have been proposed for elimination of organophosphoric pesticides. Especially, degradation of methyl-parathion has been examined by photocatalysis [2,3], hydrogen peroxide [4], ultrasonic radiation [1] or hydrolysis promoted by mercury [5]. The major disadvantage of these technologies is that they are designed for decontamination of aqueous solutions with a very low pollu-tant concentration and are not suitable for treatment of higher concentrations of pesticides.…”