Chlorination Chemistry. 1. Rate Coefficients, Reaction Mechanisms, and Spectra of the Chlorine and Bromine Adducts of Propargyl Halides (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.
Ultraviolet absorption spectra and kinetics of CH3S and CH2SH radicals
Chemical Physics Letters, 1991
Acetonyl radicals and acetonylpcroxy radicals were produced by pulse radiolysis of gas mixtures with varying concentrations of CI-I&OCH, and Oz in 1 atm of SF6 to initiate tlte reactions ( 1) F+CI-IsCOCH3-+HFfCH@CH~, (2) ZCH&OCH,-products, (3 ) CHJCOCH2+02( + M)&I-ISCOCH202( + M) and (4) 2CHsCOCHLOL+products. The ultraviolet absorption spectrum of the acetonyl radical is composed of a fairly weak band centered at 3 15 nm and a stronger band in the range of 200-250 nm. The absorption cross section has been determined, a(310 nm)=(8.73~0.50)x10-1g cm* molecule-L. The values k2= (4.8f0.4) x lo-", k,= (1.5+0.3)x lo-'* and k4= (8.3f 1.6) x 10-'zcm3 molecule-' s-' at 298 K were derived by computer modelling of the observed kinetic features. 206 0009-2614/90/$03.50 0 1990 -Elsevier Science Publishers B.V. (North-Holland) volume 173, number 2,3 CHEMICAL PHYSICS LETTERS
Journal of Physical Chemistry A, 2010
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) × 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) × 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) × 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) × 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) × 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 1σ statistical uncertainties obtained from the fitting, and the estimated overall uncertainty in the determined bimolecular rate coefficients is about (15%.
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
By using 193 nm laser photolysis and cavity ring-down spectroscopy to produce and monitor the propargyl radical (CH 2 CCH), the self-reaction and oxygen termolecular association rate coefficients for the propargyl radical were measured at 295 K between total pressures of 300 Pa and 13300 Pa (2.25 and 100 Torr) in Ar, He, and N 2 buffer gases. The rate coefficients obtained by simple second-order fits to the decay data were observed to vary with the photolytic precursors: allene, propargyl chloride, and propargyl bromide. By using a numerical fitting routine and more comprehensive mechanisms, a distinct rate coefficient for the selfreaction was determined, k ∞ (C 3 H 3 +C 3 H 3)) (4.3 (0.6) × 10-11 cm 3 molecule-1 s-1 at 295 K. This rate coefficient, which is a factor of 2.8 times slower than reported previously, was independent of total pressure and buffer choice over the entire pressure range. Other rate coefficients derived during the modeling included k(C 3 H 3 +H 665 Pa He)) (2.5 (1.1) × 10-10 cm 3 molecule-1 s-1 , k(C 3 H 3 +C 3 H 3 Cl 2)) (7 (4) × 10-11 cm 3 molecule-1 s-1 , and k(C 3 H 3 +C 3 H 3 Br 2)) (2.4 (2) × 10-11 cm 3 molecule-1 s-1. The association reaction C 3 H 3 + O 2 was found to lie in the falloff region between linear and saturated pressure dependence for each buffer gas (Ar, He, and N 2) between 300 Pa and 13300 Pa. A fit of these data derived the high-pressure limiting rate coefficient k ∞ (C 3 H 3 +O 2)) (2.3 (0.5) × 10-13 cm 3 molecule-1 s-1. Three measurements of the propargyl radical absorption cross-section obtained σ 332.5) (413 (60) × 10-20 cm 2 molecule-1 at 332.5 nm. Stated uncertainties are two standard deviations and include the uncertainty of the absorption cross section, where appropriate.
The Journal of Physical Chemistry, 1991
we find that it fails completely, emphasizing once again the difficulties one encounters in explaining the experimental results. One possibility for extending the scope of the BEBO model to embrace these reactions is to assume that the two parameters of the Sat0 triplet function, the Morse parameter 8, and S i 4 electronic dissociation energy, E,, which are interconnected, are dependent on methylation. Taking E, = 540 kJ/mol and 8 = 2.1 A-' for 0 + SiH,, and E, = 520 kJ/mol and 0 = 2.25 A-' for 0 + Me3SiH, (for other parameters see ref 1) one obtains the results presented in . The trend in the rate constants with methylation can be satisfactorily reproduced but the Arrhenius parameters and kinetic isotope effects are in much worse agreement with the corresponding experimental values than is the case for the 0 + alkane system.21
The Journal of Physical Chemistry A, 2000
Cavity ring-down (CRD) spectroscopy and ab initio calculations have determined the reaction rate coefficients, mechanism, and thermochemistry relevant to the addition of a chlorine atom to allene. Chlorine atoms were produced by laser photolysis at 351 nm and the addition reaction products were probed at a variable delay by CRD spectroscopy using a second laser pulse. Ab initio results indicate that the only persistent addition product is the 2-chloroallyl (C 3 H 4 Cl) radical. We measured the continuum spectrum of the 2-chloroallyl radical between 238 and 252 nm and determined the absorption cross section, σ 240 (C 3 H 4 Cl) ) (2.5 ( 0.5) × 10 -17 cm 2 . By fitting the C 3 H 4 Cl absorption data to complex kinetic mechanisms, rate coefficients at 298 K were found to be k(Cl+C 3 H 4 ; 656 Pa, N 2 ) ) (1.61 ( 0.27) × 10 -10 cm 3 molecule -1 s -1 , k(Cl+C 3 H 4 ; 670 Pa, He) ) (1.34 ( 0.24) × 10 -10 cm 3 molecule -1 s -1 , and k(Cl+C 3 H 4 ; 1330 Pa, He) ) (1.75 ( 0. 25) × 10 -10 cm 3 molecule -1 s -1 . The rate coefficient of the self-reaction displayed no pressure dependence between 434 and 1347 Pa in N 2 buffer giving k(C 3 H 4 Cl+C 3 H 4 Cl) ) (3.7 ( 1.0) × 10 -11 cm 3 molecule -1 s -1 . A study of the addition reaction of 2-chloroallyl radical and oxygen molecule determined σ 240 (C 3 H 4 ClO 2 ) ) (3.6 ( 0.7) × 10 -18 cm 2 and k(O 2 +C 3 H 4 Cl, 705 Pa N 2 ) ) (3.6 ( 0.4) × 10 -13 cm 3 molecule -1 s -1 . The listed uncertainties denote two standard deviations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section.
Journal of Physical Chemistry A, 1999
Reactions of methyl radicals with hydrogen bromide CH 3 + HBr f CH 4 + Br (1) and bromine atoms CH 3 + Br f CH 3 Br (2) were studied using excimer laser photolysis-transient UV spectroscopy at 297 ( 3 K over the 1-100 bar buffer gas (He) pressure range. Methyl radicals were produced by 193 nm (ArF) laser photolysis of acetone, (CH 3 ) 2 CO, and methyl bromide, CH 3 Br. Temporal profiles of methyl radicals were monitored by UV absorption at 216.51 nm (copper hollow cathode lamp with current boosting). The yield of acetyl radicals in photolysis of acetone at 193 nm was found to be less than 5% at 100 bar He based on the transient absorptions at 222.57 and 224.42 nm. The measured rate constants for reaction 1 are k 1 ) (2.9 ( 0.7) × 10 -12 , (3.8 ( 1.5) × 10 -12 , and (3.4 ( 1.3) × 10 -12 cm 3 molecule -1 s -1 at the buffer gas (He) pressures of 1.05, 11.2, and 101 bar, respectively. The rate data obtained in this study confirmed high values of the previous (low pressure) measurements and ruled out the possibility of interference of excited species. The measured rate constant is independent of pressure within the experimental error. The rate constant of reaction of methyl radicals with bromine atoms (2) was determined relative to the rate constant of methyl radical self-reaction, CH 3 + CH 3 f C 2 H 6 (3) in experiments with photolysis of CH 3 Br: k 2 /k 3 ) 0.92 ( 0.32, 1.15 ( 0.30, and 1.65 ( 0.26 at 1.05, 11.2, and 101 bar He, respectively. On the basis of the literature data for reaction 3, this yields k 2
Hydroxyl radical rate constants and photolysis rates of .alpha.-dicarbonyls
Environmental Science & Technology, 1983
Photolysis rates of glyoxal, methylglyoxal, and biacetyl and OH radical reaction rate constants for glyoxal and methylglyoxal have been determined at 298 f 2 K in an environmental chamber, by using the photolysis of CH30NO-air mixtures to generate OH radicals. The OH radical rate constants obtained were (1.15 f 0.04) X lo-'' and (1.73 f 0.13) X lo-'' cm3 molecule-l s-' for glyoxal and methylglyoxal, respectively. The photolysis rates of glyoxal, methylglyoxal, and biacetyl increased throughout this series, and average quantum yields for the wavelength region 1290 nm of 0.029 f 0.018,0.107 f 0.030, and 0.158 f 0.024 were derived for glyoxal, methylglyoxal, and biacetyl, respectively. In addition, upper limits to the rate constants for the reaction of O3 with glyoxal and methylglyoxal of <3 X and <6 X cm3 molecule-' s-l, respectively, were obtained at 298 f 2 K. These data will serve as needed input to chemical kinetic computer modeling studies of the aromatic hydrocarbons. Additionally, the a-dicarbonyls also photolyze: of the dicarbonyls and cyclohexane with-0(8P) atoms and o3 were negligible, and since dilution due to sampling was