Atmospheric Chemistry of Isopropyl Methyl Methylphosphonate and Dimethyl N,N-Dimethylphosphoroamidate

Abstract

Rate constants for the reactions of OH radicals with isopropyl methyl methylphosphonate [(CH(3))(2)CHOP(O)(CH(3))OCH(3); IMMP] and dimethyl N,N-dimethylphosphoroamidate [(CH(3)O)(2)P(O)N(CH(3))(2); DMDMPA] have been measured over the temperature range 283-350 K and atmospheric pressure of air using a relative rate method. The rate expressions obtained were 2.72 x 10(-13) e((1642+/-144)/T) cm(3) molecule(-1) s(-1) (6.72 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + IMMP and 6.05 x 10(-13) e((1185+/-144)/T) cm(3) molecule(-1) s(-1) (3.23 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + DMDMPA. In addition, rate constants for the reactions of NO(3) radicals and O(3) with IMMP were measured at 296 +/- 2 K, of (4.8 +/- 2.1) x 10(-16) and <7 x 10(-20) cm(3) molecule(-1) s(-1), respectively. Products of the OH radical-initiated reactions were investigated using gas chromatography, in situ atmospheric pressure ionization mass spectrometry (API-MS), and in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH + IMMP reaction, the major initial products appear to be CH(3)OP(O)(CH(3))OC(O)CH(3) + (*)CH(3), with subsequent reactions of the methyl radical in the presence of NO(x) leading to HCHO, CH(3)ONO, and CH(3)ONO(2). For the OH + DMDMPA reaction, (CH(3)O)(2)P(O)N(CH(3))CHO was observed as a significant product. Possible reaction mechanisms are discussed.