Kinetics of the atmospherically important gas-phase reactions of a series of trimethyl phosphorothioates

Heterogeneous ozonation of suspended malathion and chlorpyrifos particles

“…The decay rate of malathion particles and the growth rate of malaoxon (the main ozonation product) measured are $8.0 Â 10 À19 cm 3 molecule À1 s À1 . Using the formula of s O3 = 1/(k O3 Â [O 3 ]) and [O 3 ] = 7 Â 10 11 molecule cm À3 (Logan, 1985), the atmospheric lifetimes of malathion particles towards ozone reaction is $18 d. The decay rate of chlorpyrifos particles and the growth rate of chlorpyrifos oxon (the main ozonation product) measured are $1.5 Â 10 À18 cm 3 molecule À1 s À1 , which corresponds to an atmospheric lifetime of $9 d. Compared with the atmospheric lifetimes of the gas-phase O,O,S-trimethylphosphorodithioate (83 d, the analogue of malathion) and the O,O,O-trimethylthiophosphate (55 d, the analogue of chlorpyrifos) due to reaction with ozone (Goodman et al, 1988), the atmospheric lifetime of malathion and chlorpyrifos particles due to reaction with ozone are relatively shorter. The discrepancies between these atmospheric lifetimes may result from the different molecular structures of the analogues or the different circumstances of the reactions.…”

Heterogeneous atmospheric degradation of current-use pesticides by nitrate radicals

“…In the literature, some kinetic data are available for the degradation of pesticides in the gas phase, even if no data concerns the chemical families of compounds under study. (Atkinson, 1991) Degradation rate constants measured or modeled for pesticides in the gas-phase exposed to NO 3 radicals range from 10 -13 cm 3 molecule -1 s -1 to 10 -16 cm 3 molecule -1 s -1 (Table 2) ( Goodman et al, 1988;Aschmann et al, 2005aAschmann et al, , 2005bAschmann and Atkinson, 2006;Cheng et al, 2017). Heterogeneous reactivity showed degradation rate constants of about 10 -15 cm 3 molecule -1 s -1 (this study).…”

Atmospheric Chemistry of Methyl and Ethyl N,N,N′,N′-Tetramethylphosphorodiamidate and O,S-Dimethyl Methylphosphonothioate

“…This then suggests that any CH 3 S(OH)P(O)(CH 3 )OCH 3 adduct is less stable toward back-decomposition to reactants than is the CH 3 S-(OH)CH 3 adduct, with the stability of the CH 3 S(OH)P(O)-(CH 3 )OCH 3 adduct being ≤10 kcal mol −1 assuming that the rate constants for reactions 9 and 11 are similar to those for the corresponding reactions in the OH + dimethyl sulfide system. In order to explain the observed products from the reactions of OH radicals with DMMP and TEP, 8,10 it has previously been proposed 8,10 3,4 it is anticipated that CH 3 OP(S)(CH 3 )OH will be significantly more reactive than CH 3 SP(O)(CH 3 )OH toward OH radicals (because of the presence of a P=S bond, with, for example, (CH 3 O) 3 PS being a factor of ∼10 more reactive than (CH 3 O) 3 PO). Since the reactions of OH radicals with (CH 3 O) 3 PS, (CH 3 O) 2 P(S)-SCH 3 , (C 2 H 5 O) 3 PS, and (C 2 H 5 O) 2 P(S)CH 3 lead to the formation of (CH 3 O) 3 PO (in 28 ± 4% yield), 26 (CH 3 O) 2 P-(O)SCH 3 (in 13 ± 5% yield), 26 (C 2 H 5 O) 3 PO (in 60 ± 12% yield), 18 and (C 2 H 5 O) 2 P(O)CH 3 (in 21 ± 4% yield), 13…”

“…3−17 Under atmospheric conditions, reaction with OH radicals was calculated to dominate for the alkyl phosphates, phosphorothioates, phosphonates, and phosphonothioates. [4][5][6]8,10,13,15,16 ], rate constants for the OH radical reactions have been measured as a function of temperature 1 2 − 1 6 and product formation investigated. 8,10,13,15,16,18 These OH radical reactions all exhibit negative temperature dependencies, with values of B in k = A e −B/T ranging from −(474 ± 159) K for DMHP to −(1516 ± 149) K for the alkyl phosphates and phosphonates studied.…”