Gas Phase α,α Elimination of Hydrogen Halides from Halomenthanes. I. Thermal Decomposition of Chlorodifluoromethane, Trifluoromethane, and Trichloromethane Behind Shock Waves

Abstract

The thermal decomposition of CHClF2, CHF3, and CHCl3 has been studied behind incident and reflected shock waves. The unimolecular decomposition was observed to proceed via the α,α elimination reactions in agreement with previous work. The progress of reaction was monitored via time resolved absorption spectrometry of CF2 at 253 nm (for (1) and (2)) and of the secondary reaction product C2Cl4 at 230 nm (for (3)). The pressure dependence of k1, k2, and k3 was investigated over a pressure range of a factor of ∼ 100. From the experiments in the fall off region, low and high pressure limiting rate constants (k0 and k∞) were obtained by application of a modified Kassel theory. For k∞, the Arrhenius expressions were deduced. Excellent agreement with previous work is achieved for k1∞ and k2∞, provided that fall off is properly taken into account.

Catalytic pyrolysis of CHF3 over activated carbon and activated carbon supported potassium catalyst

“…CF 2ðsÞ þ F ðsÞ ! CF 3ðsÞ (8) However, the exact surface mechanism is yet unclear. At low temperatures, the high dissociation energy of carbon and fluorine bond inhibits the above reactions in the gas phase (Fig.…”

“…CF 3ðsÞ (8) CF 3ðsÞ þ F ðsÞ ! CF 4ðsÞ (9) To confirm the effect of the surface oxygen groups on pyrolysis of CHF 3 , activated carbon treated in H 2 flow at 1073 K for 3 h was examined.…”

“…Relative molar response (RMR) factors of fluorocarbons for TCD detection were experimentally obtained from standard gas mixtures, and quantification of halogenated hydrocarbons was performed with diluted halogenated hydrocarbons in nitrogen. Quantification of other species was estimated from published correlations [8][9][10].…”

Infrared chemiluminescence studies of the reactions of H atoms with CCl3, CF2Cl, and CH2CH2Cl radicals at 300 and 475 K: recombination–elimination vs. abstraction mechanisms

“…Allowing for a 5 kcal mol-' barrier for the reverse reaction, E$ was set at 60 kcal mol-' for reaction [la]. The E$ for HF elimination from CHF2Cl was assigned from the ratio of rate constants for HF and HC1 elimination and E$(Hc~) (12). The A H~~O ( C F~) = -42.6 kcal mol-' was taken from ref.…”

Kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: Inclusion of HCl elimination from CHCl3

“…Schug et al [6] also pointed out that the molecular elimination of HCl was the dominant path of CHCl 3 pyrolysis, and the highpressure limit rate constant was determined to be 1.82 × 10 14 exp(−54.49 kcal/mol/RT ) s −1 at 1050-1380 K. Herman et al [7] examined pulsed CO 2 laser multiple-photon dissociation of CDCl 3 in a molecular beam and reported that the only observed CHCl 3 reaction channel was hydrogen chloride elimination (greater than 99.1%), with no evidence of simple chlorine atom cleavage (less than 0.9%).…”