Atmospheric chemistry of diethyl methylphosphonate, diethyl ethylphosphonate, and triethyl phosphate

Rate constants for the reactions of OH radicals and NO3 radicals with diethyl methylphosphonate [DEMP, (C2H5O)(2)P(O)CH3], diethyl ethylphosphonate [DEEP, (C2H5O)(2)P(O)C2H5], and triethyl phosphate [TEP, (C2H5O)(3)PO] have been measured at 296 +/- 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10(-11) cm(3) molecule(-1) s(-1)) were as follows: DEMP, 5.78 +/- 0.24; DEEP, 6.45 +/- 0.27; and TEP, 5.44 +/- 0.20. The rate constants obtained for the NO3 radical reactions (in units of 10(-16) cm(3) Molecule(-1) s(-1)) were the following: DEMP, 3.7 +/- 1.1; DEEP, 3.4 +/- 1.4; and TEP, 2.4 +/- 1.4. For the reactions of O-3 with DEMP, DEEP, and TEP, an upper limit to the rate constant of < 6 x 10(-20) cm(3) molecule(-1) s(-1) was determined for each compound. Products of the reactions of OH radicals with DEMP, DEEP, and TEP were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEP reaction, gas chromatography with flame ionization detection (GC-FID) and in situ Fourier transform infrared (FT-IR) spectroscopy. The API-MS analyses show that the reactions are analogous, with formation of one major product from each reaction: C2H5OP(O)(OH)CH3 from DEMP, C2H5CP(O)(OH)C2H5 from DEEP, and (C2H5O)(2)P(O)OH from TER The FT-IR and GC-FID analyses showed that the major products (and their molar yields) from the TEP reaction are (C2H5O)(2)P(O)OH (65-82%, initial), CO2 (80 +/- 10%), and HCHO (55 +/- 5 %), together with lesser yields of CH3CHO (11 +/- 2%), CO (11 +/- 3%), CH3C(O)OONO2 (8%), organic nitrates (7%), and acetates (4%). The probable reaction mechanisms are discussed.