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Thermal Stability of n ‐Acyl Peroxynitrates
Author(s) -
KABIR M.,
JAGIELLA S.,
ZABEL F.
Publication year - 2014
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20862
Subject(s) - chemistry , thermal decomposition , reaction rate constant , decomposition , thermal stability , bromine , alkyl , homologous series , bar (unit) , analytical chemistry (journal) , stereochemistry , kinetics , crystallography , organic chemistry , physics , quantum mechanics , meteorology
Peroxynitrates (RO 2 NO 2 ), in particular acyl peroxynitrates (R = R′C(O) with R′ = alkyl), are prominent constituents of polluted air. In this work, a systematic study on the thermal decomposition rate constants of the first five members of the series of homologous R′C(O)O 2 NO 2 with R′ = CH 3 ( =PAN), C 2 H 5 , n ‐C 3 H 7 , n ‐C 4 H 9 , and n ‐C 5 H 11 is undertaken to verify the conclusions from previous laboratory data (Grosjean et al., Environ. Sci. Technol . 1994, 28, 1099–1105; Grosjean et al., Environ. Sci. Technol . 1996, 30, 1038–1047; Bossmeyer et al., Geophys. Res. Lett . 2006, 33, L18810) that the longer chain peroxynitrates may be considerably more stable than PAN. Experiments are performed in a temperature‐controlled, evacuable 200 L‐photoreactor made from quartz. n ‐Acyl peroxynitrates are generated by stationary photolysis of mixtures of molecular bromine, O 2 , NO 2 , and the corresponding parent aldehydes, highly diluted in N 2 . Thermal decomposition of R′C(O)O 2 NO 2 is initiated by the addition of an excess of NO. First‐order decomposition rate constants k 1 of the reactions R′C(O)O 2 NO 2 (+M) → R′C(O)O 2 + NO 2 (+M) are derived at 298 K and a total pressure of 1 bar from the measured loss rates of R′C(O)O 2 NO 2 , correcting for wall loss of R′C(O)O 2 NO 2 and several percentages of reformation of R′C(O)O 2 NO 2 by the reaction of R′C(O)O 2 radicals with NO 2 . With increasing chain length of R′, k 1 (298 K) slightly decreases from 4.4 × 10 −4 s −1 (R′ = CH 3 ) to 3.7 × 10 −4 s −1 (R′ = C 2 H 5 ), leveling off at (3.4 ± 0.1) × 10 −4 s −1 for R′ = n ‐C 3 H 7 , n ‐C 4 H 9 , and n ‐C 5 H 11 . Temperature dependencies of k 1 were measured for CH 3 C(O)O 2 NO 2 and n ‐C 5 H 11 C(O)O 2 NO 2 in the temperature range 289–308 K, resulting in the same activation energy within the statistical error limits (2σ) of 0.9 and 1.5 kJ mol −1 , respectively. A few experiments on n ‐C 6 H 13 C(O)O 2 NO 2 , n ‐C 7 H 15 C(O)O 2 NO 2 , and n ‐C 8 H 17 C(O)O 2 NO 2 were also performed, but the results were considered to be unreliable due to strong wall loss of the peroxynitrate and possible complications caused by radical‐sinitiated side reactions.