Thermal stability of Peroxynitrates

Peroxynitrates are thermally unstable intermediates (at ambient temperatures) in the atmospheric degradation of hydrocarbons. In this work, thermal lifetimes of nine peroxynitrates have been measured as a function of temperature and, for two of them, also, as a function of total pressure. In the presence of excess NO, relative concentrations of the peroxynitrates were followed in a 420 I reaction chamber as a function of time by means of longpath IR absorption using a Fourier transform spectrometer. Original data on the unimolecular decomposition rate constants are presented for the peroxynitrates RO₂NO₂ with R = C₆H₁₁, CH₃C(O)CH₂, C₆H₅CH₂, CH₂I, CH₃C(O)OC(H)CH₃, C₆H₅OCH₂, (CH₃)₂NC(O), C₆H₅OC(O), and C₂H₅C(O). Thermal lifetimes at room temperature and atmospheric pressure are very short (in the order of seconds) for substituted methyl peroxynitrates (i.e., R'CH₂O₂NO₂) but rather long for substituted formyl peroxynitrates (i.e., R″C(O)O₂NO₂). Kinetic data from this and previous work from our laboratory are used to derive structure‐stability relationships which allow an estimate of the thermal lifetimes of peroxynitrates from readily available ¹³C n.m.r. shift data. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 127–144, 1999