Heterogeneous Reactions of Pirimiphos-Methyl and Pirimicarb with NO₃ Radicals

Abstract

Pirimiphos-methyl (PMM) and pirimicarb (PM) are two typical N,N-dialkyl substituted pyrimidine pesticides. The heterogeneous reactions of suspended PMM and PM particles with NO 3 radicals are investigated using an online aerosol time-of-flight mass spectrometer and a real-time atmospheric gas analysis mass spectrometer. Three products for PMM and five products for PM are observed and assigned with the aid of GC/MS. Phosphoric acid 2-diethylamino-6-methyl-4-pyrimidinyl dimethyl ester and 2-(dimethylamino)-5,6-dimethyl-4-hydroxy-pyrimidine are the main reaction products observed for PMM and PM, respectively. The effective rate constants for the reactions of PMM and PM particles with NO 3 radicals are (9.9 ± 0.3) × 10 −12 and (7.5 ± 0.3) × 10 −13 cm 3 molecule −1 s −1 , respectively, obtained using a mixed-phase relative rate method. Geometries and energies of transition states (TS) and intermediates (IM) are obtained by DFT calculation to elucidate the detailed mechanism of the PS group oxidation into the PO group for PMM. The theoretical studies present the reasonable intermediates including the S-oxide and the diradical (IM1 a and IM2 a ). The mechanism explanation may provide useful information for understanding the degradation mechanism of organothionophosphorus compounds in the environment.

Kinetic studies of heterogeneous reactions of particulate phosmet and parathion with NO3 radicals

“…The results reveal phosmet and parathion with high reactivity toward NO 3 radicals. The calculated uptake coefficients of NO 3 radicals on phosmet and parathion particles are close to those of NO 3 radicals on pirimiphos-methyl (one typical OPPs) and pirimicarb (Wang et al, 2012).…”

“…In the previous studies, the heterogeneous reaction rates of pirimiphos-methyl with NO 3 radicals and O 3 were determined to be 9.9 Â 10 À12 and 1.97 Â 10 À17 cm 3 molecule À1 s À1 , respectively Wang et al, 2012). Compared to the results obtained in this study, the effective rate constants of phosmet and parathion with NO 3 radicals are 3 times slower than that of pirimiphos-methyl, while $5 orders of magnitude faster than that of pirimiphos-methyl with O 3 .…”

“…Considering its high concentration at night, NO 3 radicals may play an important role in controlling the lifetimes of atmospheric OPPs. However, few rate data for heterogeneous reactions of particulate OPPs with NO 3 radicals have hitherto been determined (Liu et al, 2011(Liu et al, , 2012aWang et al, 2012).…”

Heterogeneous reaction of particulate chlorpyrifos with NO 3 radicals: Products, pathways, and kinetics

“…An 8 mm diameter copper rod coupled with a cartridge heater placed in the detection chamber was used to vaporize the particles, and the nascent organic vapor was photoionized with light radiated from a laboratory-assembled VUV lamp powered by RF of 80 W [32]. The ions produced by VUV photoionization were extracted into a field-free flight distance of 1.4 m by an ion optical system and then detected by a microchannel plate detector.…”

“…The attachment of an oxygen atom is speculated to be formed by addition of NO 3 radicals, followed by a loss of a NO 2 molecule [29]. The intermediate I a then rearranges, leading to the formation of the diradical intermediate I b [32]. One evolution of I b involves the transformation of the P S double bond into the P O double bond.…”