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Heterogeneous reactions of pirimiphos-methyl and pirimicarb with NO3 radicals

Youfeng Wang1, Bo Yang, Peng Zhang

  • 1Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.

The Journal of Physical Chemistry. A
|October 23, 2012
PubMed

Insights

Pirimiphos-methyl (PMM) and pirimicarb (PM) react with NO(3) radicals, forming distinct products. DFT calculations reveal oxidation mechanisms, aiding understanding of organothionophosphorus pesticide degradation in the environment.

Area of Science:

  • Environmental Chemistry
  • Atmospheric Chemistry
  • Chemical Kinetics

Background:

  • Pirimiphos-methyl (PMM) and pirimicarb (PM) are widely used N,N-dialkyl substituted pyrimidine pesticides.
  • Understanding pesticide degradation pathways is crucial for environmental risk assessment.

Purpose of the Study:

  • To investigate the heterogeneous reactions of PMM and PM particles with NO(3) radicals.
  • To elucidate the reaction mechanisms and determine rate constants.
  • To provide insights into the environmental degradation of organothionophosphorus compounds.

Main Methods:

  • Online aerosol time-of-flight mass spectrometry and real-time atmospheric gas analysis mass spectrometry.
  • Gas chromatography-mass spectrometry (GC/MS) for product identification.
  • Mixed-phase relative rate method for rate constant determination.
  • Density Functional Theory (DFT) calculations for mechanism elucidation.

Main Results:

  • Three products for PMM and five products for PM were identified, including phosphoric acid 2-diethylamino-6-methyl-4-pyrimidinyl dimethyl ester (PMM) and 2-(dimethylamino)-5,6-dimethyl-4-hydroxy-pyrimidine (PM).
  • Effective rate constants for PMM and PM with NO(3) radicals were determined as (9.9 ± 0.3) × 10(-12) and (7.5 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), respectively.
  • DFT calculations identified key intermediates, including S-oxide and diradical species, for the oxidation of PMM's P═S group to P═O.

Conclusions:

  • The study elucidates the atmospheric degradation pathways of PMM and PM via heterogeneous reactions with NO(3) radicals.
  • The determined rate constants and identified products contribute to understanding pesticide fate in the atmosphere.
  • Theoretical calculations provide a detailed mechanistic understanding of the oxidation process, valuable for environmental impact assessments.

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