Kinetics of Cl Atom Reactions with C₂H₅Cl and C₂H₄Cl Radical and the Disproportionation of 2C₂H₄Cl at 298 K and at Millitorr Pressures

Abstract

The bimolecular reaction Cl + C2H5Cl → HCl + C2H4Cl (1) is studied in the very-low-pressure reactor (VLPR) system at room temperature. Detailed mass spectrometric analysis of simultaneous reactant consumption and product formation rates indicates that the overall mechanism also includes two disproportionation reactions: Cl + C2H4Cl → HCl + C2H3Cl (2) and 2C2H4Cl → C2H5Cl + C2H3Cl (3). Rate constants obtained for these reactions are: k 1 = (8.07 ± 0.36) × 10-12, k 2 = (1.18 ± 0.06) × 10-11, and k 3 = (1.83 ± 0.15) × 10-12 cm3/(molecule-s). The decrease in the reactivity of C2H5Cl compared with C2H6 reactivity in reaction type (1) correlates well with the electronegativity of the Cl substituent. The decrease points to a dipole−dipole repulsion in the transition state. Preliminary measurement of the reaction of C2H4Cl radical with Cl2 yields a value of k 5 = (1.7 ± 1.0) × 10-13 cm3/(molecule-s).

Evolution of Structure–Reactivity Correlations for the Hydrogen Abstraction Reaction by Chlorine Atom

“…Both of these complications − can be minimized by judicious choice of initial concentrations. A few reports exist for very low pressure conditions (VLPR) with mass spectroscopic detection, , but the reliability of the technique has been questioned …”

“…It has been suggested that k for polyfluoroalkanes is inversely proportional to their computed hardness, that is, (IE – EA)/2; in other words, increasing softness promotes charge transfer and facilitates reaction . An attempt to apply Pauling electronegativities to correlate k for polychloro ethers was only modestly successful; this independent variable was also suggested for alkyl halides . Unfortunately, these independent variables are not widely available for the cases in Table .…”

“…Both of these complications 16−18 can be minimized by judicious choice of initial concentrations. A few reports exist for very low pressure conditions (VLPR) with mass spectroscopic detection, 19,20 but the reliability of the technique has been questioned. 21 Many more k Σ values are available from competitive relative rate experiments in which a mixture of RH and an added reference compound, whose k Σ,ref is already known from an absolute measurement, is steadily photochlorinated to significant conversion levels.…”

Quantum Chemical Molecular Dynamics Simulations of 1,3-Dichloropropene Combustion

“…The oxidative decomposition of halogenated hydrocarbons have been investigated on a number of occasions. − ,− Recent studies suggest that the thermal decomposition of chlorinated straight-chain hydrocarbons proceeds via a unimolecular C–Cl bond scission at the allylic carbon, due to this C–Cl bond being weaker compared to other C–H bonds. , The primary chemical products (∼90%) of 1,3-D thermolysis are CO, CO 2 , H 2 O, and HCl . HCl formation can occur via H abstraction by Cl from the parent compound and its derived radicals − or via an intra-annular HCl elimination. ,,,− However, combustion of non-chlorinated analogous species shows that O 2 abstraction of an allylic H, forming the HO 2 radical, is also an important initiation step. − This HO 2 radical is converted to the relatively more stable OH radical by reactions with 1,3-D and allylic radicals, additionally forming aldehydes/ketones and aldehydic/ketonic radicals. − The latter can undergo unimolecular or bimolecular C–C bond scissions to form CO or react with O 2 to form an alkylperoxy radical, which can readily react with alkenes to form alkoxides and CO 2 . − H 2 O is formed mainly by abstraction or combination reactions of H with OH. ,,− Previously, molecular dynamics (MD) has proved to be an invaluable tool in revealing reaction initation pathways in the combustion of methane, , n -dodecane, phenol, , and benzene . However, the ...…”

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

“…Kaiser et al , have studied the CH 3 CHCl + Cl 2 reaction with respect to the CH 3 CHCl + O 2 reaction using relative rate method and initiating the reactions using 351 nm photolysis of Cl 2 in a reaction cell ( T = 298 K, 700 Torr of N 2 ) and employing absorption spectroscopy for product analysis. Dobis and Benson measured the kinetics of CH 3 CHCl + Cl 2 reaction under very low pressure conditions (VLPR-method) at room temperature.…”