Kinetics of the Reactions of CH2Cl, CH3CHCl, and CH3CCl2 Radicals with Cl2 in the Temperature Range 191−363 K (original) (raw)
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The Journal of Physical Chemistry, 1991
The gas-phase kinetics of the reactions of four partially halogenated methyl radicals (CH,Cl, CH2Br, CH21, and CHC12) with Cl, have been studied as a function of temperature using a tubular reactor coupled to a photoionization mass spectrometer. Radicals were homogeneously generated by pulsed 193-and/or 248-nm laser photolysis. Decays of the radical concentrations were monitored in time-resolved experiments as a function of [Cl,] to obtain bimolecular rate constants for the R + C1,-RCI + C1 reactions studied. The following Arrhenius expressions (k = A exp(-E/RT)) were obtained (the numbers in brackets are log (A/(" molecule-' s-')), E/(kJ mol-I); the temperature ranges are also indicated): R = CH2Cl [-11.82 f 0.12, 4.1 f 1.3, 295-719 K]; R = CH2Br [-11.91 * 0.14,2.4 f 1.4, 295-524 K]; R = CH21 [-11.94 * 0.19, 0.8 & 2.2, 295-524 K]; R = CHC12 [-12.07 * 0.15, 10.3 f 2.0, 357-719 K]. Errors are lu, including both random and an estimated 20% systematic error in the individual bimolecular rate constants. The Arrhenius parameters of these and two other R + C12 reactions are compared with theoretical determinations based on semiempirical AM1 calculations of transition-state energies, structures, and vibration frequencies. The calculations qualitatively reproduce the obsehed trends in both the Arrhenius A factors and in the activation energies. The use of molecular properties to account for reactivity differences among all the R + C12 reactions which have been studied to date are also explored using free-energy correlations with these properties.
The Journal of Physical Chemistry A, 2005
The kinetics of the reactions of chlorinated methyl radicals (CH 2 Cl, CHCl 2 , and CCl 3 ) with NO 2 have been studied in direct measurements at temperatures between 220 and 360 K using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals have been homogeneously generated at 193 or 248 nm by pulsed laser photolysis of appropriate precursors. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of NO 2 being in large excess over radical concentrations. The bimolecular rate coefficients of all three reactions are independent of the bath gas (He or N 2 ) and pressure within the experimental range (1-6 Torr) and are found to depend on temperature as follows: k(CH 2 Cl + NO 2 ) ) (2.16 ( 0.08) × 10 -11 (T/300 K) -1.12(0.24 cm 3 molecule -1 s -1 (220-363 K), k(CHCl 2 + NO 2 ) ) (8.90 ( 0.16) × 10 -12 (T/300 K) -1.48(0.13 cm 3 molecule -1 s -1 (220-363 K), and k(CCl 3 + NO 2 ) ) (3.35 ( 0.10) × 10 -12 (T/300 K) -2.2(0.4 cm 3 molecule -1 s -1 (298-363 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are about (25%. In the reactions CH 2 Cl + NO 2 , CHCl 2 + NO 2 , and CCl 3 + NO 2 , the products observed are formaldehyde, CHClO, and phosgene (CCl 2 O), respectively. In addition, a weak signal for the HCl formation has been detected for the CHCl 2 + NO 2 reaction.
International Journal of Chemical Kinetics, 1986
The kinetics of the reactions of CH21, CH2Br, CH2CI, and CHCI2 with HI were studied in a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature (typically between 294 and 552 K) to determine Arrhenius parameters. For these and other R + HI reactions studied to date (Le,, those involving alkyl radicals), a linear free energy relationship was discovered which correlates the large differences in reactivity among all these R + HI reactions with the inductive effect of the substituent atoms or groups on the central carbon atom.
The Journal of Physical Chemistry A, 1999
Cavity ring-down spectroscopy (CRDS), end-product analysis, and ab initio calculations have determined absorption cross sections, rate coefficients, reaction mechanisms, and thermochemistry relevant to the addition of halogen atoms to propargyl chloride and propargyl bromide. Halogen atoms were produced by laser photolysis, and the addition reaction products were probed at a variable delay by CRDS using a second laser pulse. We report the continuum spectra of C 3 H 3 Cl 2 (1,2-dichloroallyl), C 3 H 3 ClBr (1-chloro-2-bromoallyl), and C 3 H 3 Br 2 (1,2-dibromoallyl) radicals between 238 and 252 nm and the absorption cross sections, σ 240 (C 3 H 3 -Cl 2 ) ) (4.20 ( 1.05) × 10 -17 cm 2 molecule -1 and σ 242 (C 3 H 3 Br 2 ) ) (1.04 ( 0.31) × 10 -17 cm 2 molecule -1 . When the observed data are fit to complex reaction schemes, the 298 K rate coefficients for formation of 1,2-dihaloallyl radicals at 665 Pa were found to be k(Cl + C 3 H 3 Cl) ) (1.2 ( 0.2) × 10 -10 cm 3 molecule -1 s -1 and k(Br + C 3 H 3 Br) ) (2 ( 1) × 10 -12 cm 3 molecule -1 s -1 . At 298 K and 665 Pa the self-reaction rate coefficients of these radicals were found to be k(C 3 H 3 Cl 2 + C 3 H 3 Cl 2 ) ) (3.4 ( 0.9) × 10 -11 cm 3 molecule -1 s -1 and k(C 3 H 3 Br 2 + C 3 H 3 Br 2 ) ) (1.7 ( 1.1) × 10 -11 cm 3 molecule -1 s -1 . The listed uncertainties are twice the standard deviation of individual determinations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section. † NIST/NRC Postdoctoral Associate 1995-1997.
International Journal of Chemical Kinetics, 1999
A laser photolysis-long path laser absorption (LP-LPLA) experiment has been used to determine the rate constants for H-atom abstraction reactions of the dichloride radical anion (Cl 2 Ϫ ) in aqueous solution. From direct measurements of the decay of Cl 2 Ϫ in the presence of different reactants at pH ϭ 4 and I ϭ 0.1 M the following rate constants at T ϭ 298 K were derived: methanol, (5.1 Ϯ 0.3) · 10 4 M Ϫ1 s Ϫ1 ; ethanol, (1.2 Ϯ 0.2) · 10 5 M Ϫ1 s Ϫ1 ; 1-propanol, (1.01 Ϯ 0.07) · 10 5 M Ϫ1 s Ϫ1 ; 2-propanol, (1.9 Ϯ 0.3) · 10 5 M Ϫ1 s Ϫ1 ; tert.-butanol, (2.6 Ϯ 0.5) · 10 4 M Ϫ1 s Ϫ1 ; formaldehyde, (3.6 Ϯ 0.5) · 10 4 M Ϫ1 s Ϫ1 ; diethylether, (4.0 Ϯ 0.2) · 10 5 M Ϫ1 s Ϫ1 ; methyltert.-butylether, (7 Ϯ 1) · 10 4 M Ϫ1 s Ϫ1 ; tetrahydrofuran, (4.8 Ϯ 0.6) · 10 5 M Ϫ1 s Ϫ1 ; acetone, (1.41 Ϯ 0.09) · 10 3 M Ϫ1 s Ϫ1 . For the reactions of Cl 2 Ϫ with formic acid and acetic acid rate constants of (8.0 Ϯ 1.4) · 10 4 M Ϫ1 s Ϫ1 (pH ϭ 0, I ϭ 1.1 M and T ϭ 298 K) and (1.5 Ϯ 0.8) ⅐ 10 3 M Ϫ1 s Ϫ1 (pH ϭ 0.42, I ϭ 0.48 M and T ϭ 298 K), respectively, were derived.
The Journal of Physical Chemistry A, 1998
The kinetics of the reactions CH 3 CCl 2 + O 2 h CH 3 CCl 2 O 2 f products (1) and (CH 3 ) 2 CCl + O 2 h (CH 3 ) 2 -CClO 2 f products (2) have been studied using laser photolysis/photoionization mass spectrometry. Decay constants of the radicals were determined in time-resolved experiments as a function of temperature (299-1000 K (reaction 1) and 299-700 K (reaction 2)) and bath gas density ([He] ) (3-48) × 10 16 molecules cm -3 (reaction 1) and (3-24) × 10 16 molecules cm -3 (reaction 2)). At room temperature the rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature ranges 430-500 K (reaction 1) and 490-550 K (reaction 2). Equilibrium constants were determined as functions of temperature and used to obtain the enthalpies of the addition step of the reactions 1 and 2. At high temperatures (600-700 K) the rate constant of reaction 2 is independent of both pressure and temperature within the uncertainty of the experimental data and equal to (1.72 ( 0.24) × 10 -14 cm 3 molecule -1 s -1 . The rate constant of reaction 1 is independent of pressure within the experimental range and increases with temperature in the high-temperature region: k 1 -(791 K e T e 1000 K) ) (1.74 ( 0.36) × 10 -12 exp(-6110 ( 179 K/T) cm 3 molecule -1 s -1 . Structures, vibrational frequencies, and energies of several conformations of CH 3 CCl 2 O 2 , (CH 3 ) 2 CCl, and (CH 3 ) 2 CClO 2 were calculated using ab initio UHF/6-31G** and MP2/6-31G** methods. The results were used to calculate the entropy changes of the addition reactions: ∆S°2 98 ) -159.6 ( 4.0 J mol -1 K -1 (reaction 1) and ∆S°2 98 ) -165.5 ( 6.0 J mol -1 K -1 (reaction 2). These entropy changes combined with the experimentally determined equilibrium constants resulted in the R-O 2 bond energies: ∆H°2 98 ) 112.2 ( 2.2 kJ mol -1 (reaction 1) and ∆H°2 98 ) 136.0 ( 3.8 kJ mol -1 (reaction 2).
Kinetics and Thermochemistry of the Reaction of 1-Chloroethyl Radical with Molecular Oxygen
The Journal of Physical Chemistry, 1995
The kinetics of the reaction CH3CHC1+ 0 2 F?. CH3CHC102products (1) has been studied at temperatures 296-839 K and He densities of (3-49) x 10l6 molecule cm-3 by laser photolysis/photoionization mass spectrometry. Rate constants were determined in time-resolved experiments as a function of temperature and bath gas density. At low temperatures (298-400 K) the rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature range 520-590 K. Equilibrium constants were determined as a function of temperature and used to obtain the enthalpy and entropy of the addition step of the reaction (1). At high temperatures (750-839 K) the reaction rate constant is independent of both pressure and temperature within the uncertainty of the experimental data and equal to (1.2 f 0.4) x cm3 molecule-' s-'. Vinyl chloride (C2H3C1) was detected as a major product of reaction 1 at T = 800 K. The rate constant of the reaction CH3CHC1 + C12 products (6) was determined at room temperature and He densities of (9-36) x 10l6 molecule cm-3 using the same technique. The value obtained is k6 = (4.37 f 0.69) x cm3 molecule-' s-'. An estimate of the high-pressure limit for reaction 1 was determined using this measured k6 and the kl/k6 ratio obtained by Kaiser et al.:l k"1 (T=298K) = (1.04 f 0.22) x lo-" cm3 molecule-' s-'. In a theoretical part of the study, structure, vibrational frequencies, and energies of nine conformations of CH3CHC102 were calculated using ab initio UHF/6-31G* and MP2/6-31G** methods. The theoretical results are used to calculate the entropy change of the addition reaction As0298 =-152.3 f 3.3 J mol-' K-'. Th~s entropy change combined with the experimentally determined equilibrium constants resulted in a CH3CHC1-02 bond energy m 2 9 8 =-131.2 f 1.8 kJ mol-l. The rooq-temperature entropy (S O 2 9 8 = 341.0 f 3.3 J mol-' K-') and the heat of formation (A H f o~9 8 =-54.7 f 3.7 kJ mol-') of the CH3CHC102 adduct were obtained.
The Journal of …, 2000
The photolysis of Na 2 S 2 O8 aqueous solutions containing Clions is a clean method for kinetic studies of the species Cl • / Cl 2 •in the absence and presence of added aromatic substrates. Laser and conventional flashphotolysis techniques were employed to investigate the aqueous phase reactions of chlorine atoms and Cl 2 •-(340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl 2 •in aqueous solutions containing chloride ion concentrations in the range 1 × 10 -4 to 0.6 M, total radical (Cl • + Cl 2 •-) concentrations in the range (0.1-1.5) × 10 -5 M, and pH in the range 2.5-3.0. Interpretation of the experimental data is supported by kinetic computer simulations. The rate constants 6 × 10 9 M -1 s -1 e k e 1.2 × 10 10 M -1 s -1 and < 1 × 10 5 M -1 s -1 were determined for the reactions of Cl • and Cl 2 •with benzene, respectively, in the aqueous phase. The organic radicals produced from these reactions exhibit an absorption band with maximum at 300 nm, which was assigned to a Cl-cyclohexadienyl radical (Cl-CHD). The kinetic analysis of the traces supports a reversible reaction between O 2 and Cl-CHD. A reaction mechanism leading to the formation of chlorobenzene is proposed.
The Journal of Physical Chemistry, 1991
The kinetics of reaction 1, CCI, + O2 + M-CCI3O2 + M, has been investigated in detail as a function of temperature and Over a large pmure range. At low pressure, 0.8-12 Torr, the reaction was investigated by laser photolysis and timeresolved mass spectrometry, while at high pressure (760 Torr), flash photolysis with UV absorption spectrometry was employed. At the low-pressure limit, the rate expression, k,(O) = (1.6 f 0.3) X 10-'(T/298)*6.3fo") cm6 molecule-2 s-' (M = N2), exhibits a quite strong negative temperature coefficient. The obtained strong collision rate expression, 7.0 X T/298y3 cm6 molecule-2 s-I, using either RRKM calculations or Troe's factorized expression, is unable to reproduce the experimental temperature dependence, unless an unreasonably strong temperature dependence is assigned to the collisional efficiency factor: = 0.23(T/298)-2.0 (M = N2). Similar results are obtained for other chlorofluoromethyl radicals. The falloff curves were constructed by using RRKM calculations obtained by adjusting 8, and the transition-state model, in order to reproduce the experimental data. The rate expression at the high-pressure limit was derived from these calculations kl(-) = (3.2 i 0.7) X 10-'2(T/298)-(1.2M.4) cm3 molecule-I s-l. All the parameters to be used in Troe's analytical expression for calculating the bimolecular rate constant at any pressure and temperature are given. The rate constant at the low-pressure limit kl(0) is more than an order of magnitude lower than for the CF, radical. The RRKM calculations show that this arises from a large difference in the CO bond dissociation energies in the corresponding peroxy radicals: 81.9 kJ mol-] for CC1302 instead of-145 kJ mol-' for CF3O2.