Kinetic Studies of the Reactions of Atomic Hydrogen with Iodoalkanes

Abstract

Rate constants for the reaction of H atoms with the alkyl iodides iodomethane (1), deuterated iodomethane (1d), iodoethane (2), 2-iodopropane (3), and 2-iodo-2-methyl propane (4) have been measured using the flash-photolysis resonance fluorescence technique. The results are k 1 ) (6.3 ( 0.6) × 10 -11 exp [((-5(T ) 295 K) and k 4 ) 2.0 × 10 -11 (T ) 294 K) cm 3 molecule -1 s -1 . The transition state for the substitution reaction H + CH 3 I f I + CH 4 was characterized at the Gaussian-2 level of ab initio theory, and the process was shown to be slow. Evidence is presented showing that H-atom abstraction is also slow, and that the dominant pathway for the reactions of H atoms with iodoalkanes is I-atom abstraction.

Kinetic Analysis of Ethyl Iodide Pyrolysis Based on Shock Tube Measurements

“…The uncertainty limits are indicated only in the temperature range of our measurements (950-1400 K). The numbered thin lines show previously published rate coefficients: (1) Kumaran et al [20] (p = 0.1-0.7 bar), (2) Yang and Conway [25] (p = 0.02 bar), (3) Shilov and Sabirova [26], (4) Ogg [27] (p = 0.2 bar), (5) Sullivan [17] (p = 0.2 bar), (6) Yang and Tranter [19] (p = 0.07-0.16 bar; plotted values are the high-pressure extrapolation), (7) Benson and Bose [28] (p = 0.08-0.25 bar), (8) Butler and Polanyi [29] (p = 0.002-0.017 bar), (9) Michael et al [11], (10) Vasileiadis and Benson [13], (11) Baulch et al [9], (12) Lorenz et al [16], (13) Sullivan [30], and (14) Yuan et al [21] Arrhenius parameters showed a significantly better agreement with the experimental results compared to the simulations performed with the initial parameters.…”

“…Note that these Arrhenius parameters were fitted to their experimental data, but this rate coefficient was influential only in the first 2 µs of their experimental curves (see the comment on p. 441 in ). Yuan et al also measured the rate coefficient of reaction (R5), but in a different temperature region (295–624 K). Westbrook and Dryer provided an estimation of the Arrhenius parameters of (R5), but it was not included in Fig.…”

Infrared chemiluminescence: Evidence for adduct formation in the H + CH2XI reaction and studies of the N + CH2X (X = Cl/F/I/H) reactions

“…Iodine atom abstraction reactions by H atoms are usually fast and the Kansas State Laboratory has successfully used the reaction of iodoalkanes with H atom as precursor for various radicals. [1][2][3][4] For example, the rate constants for the H þ CF 3 I=CH 3 I reactions [5][6][7] are both about 1 Â 10 À11 cm 3 molecule À1 s À1 . As the investigation proceeded, it was realized that the primary reaction, H þ CH 2 ClI, was interesting and needed to be characterized on its own merit.…”

A kinetic study of the reaction of atomic hydrogen with iodobenzene

“…Reactions of hydrogen atoms with alkyl iodides have been the subject of several kinetic studies [1][2][3][4][5][6][7], motivated in part by the potential contributions of iodine to combustion chemistry [8]. Interesting kinetics have been observed in some cases, such as Cl-atom addition [9] and O-atom addition followed by elimination of HOI [10].…”

“…Rather less attention has been paid to aryl iodides, which are of fundamental interest because they exhibit a range of mechanisms in radical reactions. For example, the reaction CH 3 + C 6 H 5 I appears to proceed via I-atom abstraction [11], as does I + C 6 H 5 I [12]. The Cl + C 6 H 5 I reaction was proposed to take place by an addition/I-atom elimination path [13], while OH + C 6 H 5 I appears to take place by addition below room temperature, and by H-atom abstraction at higher temperatures [14].…”