Environ. Sci. Technol. 1989, 23, 243-244
Lambert, J. L.; Trump, E. L.; Paukstelis, J. V. Environ. Sci. Technol. 1987,21, 497. Lambert, J. L.; Liaw, Y.-L.; Paukstelis, J. V.; Chiang, Y. C. Environ. Sci. Technol. 1987, 21, 500. Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Interscience: New York, 1966; p 124.
(10) Flamm, D. L. Environ. Sci. Technol. 1977, 11, 978.
Received for review November 30,1987. Accepted August 1,1988. This research was supported in part by National Science Foundation Grant CHE-8311011.
Product Formation from the Gas-Phase Reactions of the OH Radical with (CH,O),PS and (CH30)2P(S)SCH3 Roger Atkinson," Sara M. Aschmann, Janet Arey, Patricia A. McElroy, and Arthur M. Winer
Statewide Air Pollution Research Center, University of California, Riverside, California 92521 were generated, at concentrations of (3-5) X lo7molecule ~ m - by ~ ,the photolysis of methyl nitrite in air, CH30 + NO CH30N0 + hv CH30 O2 HCHO H 0 2 HO2 + NO NO2 OH and NO was added to the reactant mixtures to avoid the formation of O3 and NO3 radicals. The initial reactant concentrations were as follows: (CH30)3PSor (CH30),P~; (when (S)SCH3, -2.4 X 1013 molecule ~ m - CH30N0 present), -2.4 X 1014molecule ~ m -and ~ ; NO, -2.4 X 1014 molecule ~ m - ~ Experiments . were carried out in a 6400-L all-Teflon chamber, equipped with black-light irradiation, at 296 f 2 K and -740 Torr total pressure of pure dry air Introduction (10). Irradiations were carried out at 50% of the maximum light intensity, with irradiation times of 2 and 4 min. Organophosphorus compounds containing the thiophosphoryl (P=S) bond, including demeton, diazinon, Gas samples of 100 cm3 were collected prior to and during the irradiations on Tenax GC solid adsorbent malathion, parathion, and phorate, are widely used insecticides in agricultural operations (1). Laboratory and (60/80 mesh) cartridges for analyses by gas chromatogambient air data have shown that for parathion and certain raphy with flame-ionization detection (GC-FID) and comother organophosphorus compounds containing the thiobined gas chromatography-mass spectrometry (GC-MS). phosphoryl bond, reaction occurs rapidly under atmosQuantitative GC-FID analyses were carried out by therpheric or simulated atmospheric conditions to transform mally desorbing the samples collected on Tenax solid adthe thiophosphoryl bond into a phosphoryl (P=O) bond sorbent at -525 K onto the head of a 15-m DB-5 Mega(2-5). Furthermore, the available evidence (2) suggests bore column (0.5-mm diameter, J&W Associates, Inc.) held that this conversion of parathion [p-o2NC6H40P(S)- at 273 K. The column was then temperature programmed from 273 to 473 K at 8 K m i d . Semiquantitative GC-MS after (OCzHs)2]to paraoxon [p-02NC6H40P(0)(OC2Hs)2] application of parathion occurs in the vapor phase. analyses also utilized thermal desorption of Tenax solid Recently, we have investigated the kinetics of the poadsorbent samples in the injection port of a Hewletttentially atmospherically important gas-phase reactions Packard 5890 GC, with cold trapping onto the head of an of a series of simple organophosphorus compounds (6-9) -40 m X 0.2 mm diameter cross-linked 5% phenylmethyl and have shown that for the trimethyl phosphorothioates silicone capillary column (Hewlett-Packard) at liquid nithe only significant atmospheric gas-phase chemical loss trogen temperature. The column was temperature proprocess is by reaction with the OH radical (6, 7,9), with grammed to 373 K at 20 K min-l and then at 10 K min-' no reaction being observed with the NO3 radical or 03. to 523 K while the HP 5970A Mass Selective Detector was From the kinetic data obtained, the majority (-85%) of in the scanning mode (40-400 amu). the OH radical reactions with O,O,O-trimethyl phosphoTrimethyl phosphate [ (CH30),PO] was obtained from rothioate [ (CH30),PS] and O,O,S-trimethyl phosphorothe Aldrich Chemical Co. and used as received. (CH3dithioate [(CH30)2P(S)SCH3]were postulated to occur by O),PS, (CH30)2P(S)SCH3,and (CH30)zP(0)SCH3were initial OH radical addition to the thiophosphoryl bond, available from our previous synthesis (7). These (CH3with the remainder occurring by H atom abstraction from O)3PS and (CH30)2P(S)SCH3 reactants contained small the C-H bonds of the CH30 or CH3S substituent groups amounts of (CH30)3P0(-7%) and (CH30)zP(0)SCH3 (-l%),respectively. Methyl nitrite was prepared as de(7). In this work, we have investigated the products formed scribed by Taylor et al. (11) and stored at 77 K under from the gas-phase OH radical initiated reactions, in the vacuum. presence of NO, of (CH30)3PSand (CH30)2P(S)SCH3, Results and Discussion with the major goal being to determine whether or not the corresponding +P=O compounds are formed from the A series of CH,ONO-NO-air and NO-air irradiations +P=S reactants and, if so, in what yield. of (CH,O),PS and (CH30)2P(S)SCH3were carried out. In the CHsONO-NO-air irradiations, the GC-FID analyses Experimental Section showed that up to -60% of the initially present (CH3The experimental methods used were generally similar O)3PSand (CH30)2P(S)SCH3 reacted and that (CH,O),PO to those used in our kinetic studies (7). Hydroxyl radicals and (CH30)2P(0)SCH3, respectively, were formed. This The products of the gas-phase reactions of the OH radical with (CH30)3PSand (CH30)2P(S)SCH3 have been investigated at room temperature and 1 atm air by gas chromatography and combined gas chromatrography-mass spectrometry. The only products observed from these reactions were (CH30)3P0 from (CH30)3PSand (CH3O)2P(0)SCH3from (CH30)2P(S)SCH3,with formation yields of 0.28 f 0.04 and 0.13 f 0.05, respectively. While the majority of the reaction products were not accounted for, these data may account for the observations of a rapid transformation of organophosphorus compounds containing a thiophosphoryl bond to their corresponding analogues containing a phosphoryl bond in ambient air.
0013-936X/89/0923-0243$01.50/0
0 1989 American Chemical Society
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Flgure 1. Plots of the amounts of (CH,0)3P0 and (CH,O),P(O)SCH, formed (corrected for reaction with the OH radical; see text) against the amounts of (CH30)3PSand (CH,O),P(S)SCH,, respectively, consumed by reactlon with the OH radical.
consumption of the +P=S reactants and the concurrent formation of the respective + P = O products was confirmed by the GC-MS analyses, which verified the identities of the products. In the NO-air irradiation (i.e., in the presence of much reduced OH radical concentrations), essentially no losses of the reactant trimethyl phosphorothioates were observed within the GC-FID measurement uncertainties of
