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Kinetics and mechanism associated with the reactions of hydroxyl radicals and of chlorine atoms with 1‐propanol under near‐tropospheric conditions between 273 and 343 K
Author(s) -
Cheema Shahbaz A.,
Holbrook Kenneth A.,
Oldershaw Geoffrey A.,
Walker Raymond W.
Publication year - 2002
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.10027
Subject(s) - chemistry , radical , reaction rate constant , reactivity (psychology) , molecule , chlorine atom , chlorine , kinetics , hydroxyl radical , atmospheric temperature range , medicinal chemistry , analytical chemistry (journal) , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics , meteorology
Rate constants for the reactions of OH radicals and Cl atoms with 1‐propanol (1‐C 3 H 7 OH) have been determined over the temperature range 273–343 K by the use of a relative rate technique. The value of k (Cl + 1‐C 3 H 7 OH) = (1.69 ± 0.19) × 10 −12 cm 3 molecule −1 s −1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k (OH + 1‐C 3 H 7 OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10 −12 cm 3 molecule −1 s −1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k (OH + 1‐C 3 H 7 OH) = 4.69 × 10 −17 T 1.8 exp(422/ T ) cm 3 molecule −1 s −1 , which fits each data point to better than 2%. Two well‐established structure–activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1‐C 3 H 7 OH, provided the β‐CH 2 group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH 2 group in alkanes at 298 K. A quantitative product analysis was carried out at 298 K for the Cl‐initiated photooxidation of 1‐C 3 H 7 OH, using both FTIR and gas chromatography. HCHO, CH 3 CHO, and C 2 H 5 CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH 3 CHO]/[C 2 H 5 CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C 2 H 5 CHO, CH 3 CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH 3 CH 2 CHOH, CH 3 CHCH 2 OH, and CH 2 CH 2 CH 2 OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α‐, β‐, and γ‐CH positions in 1‐C 3 H 7 OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 110–121, 2002