Kinetics of the Reactions of CH₂Cl, CH₃CHCl, and CH₃CCl₂ Radicals with Cl₂ in the Temperature Range 191−363 K

Abstract

The kinetics of three chlorinated free radical reactions with Cl(2) have been studied in direct time-resolved measurements. Radicals were produced in low initial concentrations by pulsed laser photolysis at 193 nm, and the subsequent decays of the radical concentrations were measured under pseudo-first-order conditions using photoionization mass spectrometer (PIMS). The bimolecular rate coefficients of the CH(3)CHCl + Cl(2) reaction obtained from the current measurements exhibit negative temperature dependence and can be expressed by the equation k(CH(3)CHCl + Cl(2)) = ((3.02 +/- 0.14) x 10(-12))(T/300 K)(-1.89+/-0.19) cm(3) molecule(-1) s(-1) (1.7-5.4 Torr, 191-363 K). For the CH(3)CCl(2) + Cl(2) reaction the current results could be fitted with the equation k(CH(3)CCl(2) + Cl(2)) = ((1.23 +/- 0.02) x 10(-13))(T/300 K)(-0.26+/-0.10) cm(3) molecule(-1) s(-1) (3.9-5.1 Torr, 240-363 K). The measured rate coefficients for the CH(2)Cl + Cl(2) reaction plotted as a function of temperature show a minimum at about T = 240 K: first decreasing with increasing temperature and then, above the limit, increasing with temperature. The determined reaction rate coefficients can be expressed as k(CH(2)Cl + Cl(2)) = ((2.11 +/- 1.29) x 10(-14)) exp(773 +/- 183 K/T)(T/300 K)(3.26+/-0.67) cm(3) molecule(-1) s(-1) (4.0-5.6 Torr, 201-363 K). The rate coefficients for the CH(3)CCl(2) + Cl(2) and CH(2)Cl + Cl(2) reactions can be combined with previous results to obtain: k(combined)(CH(3)CCl(2) + Cl(2)) = ((4.72 +/- 1.66) x 10(-15)) exp(971 +/- 106 K/T)(T/300 K)(3.07+/-0.23) cm(3) molecule(-1) s(-1) (3.1-7.4 Torr, 240-873 K) and k(combined)(CH(2)Cl + Cl(2)) = ((5.18 +/- 1.06) x 10(-14)) exp(525 +/- 63 K/T)(T/300 K)(2.52+/-0.13) cm(3) molecule(-1) s(-1) (1.8-5.6 Torr, 201-873 K). All the uncertainties given refer only to the 1sigma statistical uncertainties obtained from the fitting, and the estimated overall uncertainty in the determined bimolecular rate coefficients is about +/-15%.

An Experimental Study of the Kinetics of the Reactions of Isopropyl,sec-Butyl, andtert-Butyl Radicals with Molecular Chlorine at Low Pressures (0.5-7.0 Torr) in the Temperature Range 190-480 K

“…are considered, one can see that the behavior of the fluorinated radicals differ from the other radicals in the correlation. We have seen this behavior for fluorinated radicals in the correlations before in our previous studies of R ● +Cl 2 and R ● +NO 2 reactions . In these studies, the correlation between log 10 ( k 300 K ) and Δ electronegativity was investigated and a clear difference in behavior was observed between fluorine‐substituted methyl radicals and other halogen‐substituted methyl radicals.…”

“…Poutsma observed a good linear correlation between the log 10 ( k 300 K ) value of a reaction and the ∑ 3 i = 1 σ p, i value of the reacting radical, where ∑ 3 i = 1 σ p, i is the sum of the Hammett σ p constants of the three substituents (see Table S1 in the Supporting Information). We combined our current measurements with previous data and plotted k 300 K against ∑ 3 i = 1 σ p, i . As can be seen from Fig.…”

Review of Rate Constants and Exploration of Correlations of the Halogen Transfer Reaction of Trisubstituted Carbon-Centered Radicals with Molecular Halogens

“…The kinetic database is most extensive for chlorine transfer. Experimental gas-phase data for k Cl (R • ) are collected in Table . − Structures labeled with simple numerals result from single reported measurements or from fits to multiple measurements (see text); such multiple measurements are indicated by the same numeral but with an alphabetic suffix added. Only the numerals without letter suffixes indicate the values of k Cl,298 (R • ) used for regression analyses.…”

“…Only the numerals without letter suffixes indicate the values of k Cl,298 (R • ) used for regression analyses. The majority have been obtained from the PLP/PIMS method, − ,− ,,, along with several from the k Cl / k O 2 – k O 2 method ,,− ,,,− , and from the rotating sector method. ,− Note that the substituents on the radical center are heavily weighted toward alkyl groups and halogen atoms, with limited representation from other heteroatoms (a few O and S but no N) or carbon-centered substituents such as carbonyl. To obtain even these few, more indirect methods and kinetic assumptions were often necessary.…”

Theoretical study on the reaction of CH3CHCl + NO2

“…Chlorinated alkyl radicals such as CHCl 2 , CH 2 Cl, CH 3 CHCl and CH 3 CCl 2 are important intermediates in combustion processes, especially in the incineration of hazardous wastes [1][2][3][4] and in industry as well as other chlorination reactions of organic species [5,6]. In addition, they can also increase soot formation in fuelrich oxidation [7] and are connected with stratospheric ozone depletion [8,9].…”