Studies of the Kinetics and Thermochemistry of the Forward and Reverse Reaction Cl + C₆H₆ = HCl + C₆H₅

Abstract

The laser flash photolysis resonance fluorescence technique was used to monitor atomic Cl kinetics. Loss of Cl following photolysis of CCl 4 and NaCl was used to determine k(Cl + C 6 H 6 ) ) 6.4 × 10 -12 exp(-18.1 kJ mol -1 /RT) cm 3 molecule -1 s -1 over 578-922 K and k(Cl + C 6 D 6 ) ) 6.2 × 10 -12 exp(-22.8 kJ mol -1 /RT) cm 3 molecule -1 s -1 over 635-922 K. Inclusion of literature data at room temperature leads to a recommendation of k(Cl + C 6 H 6 ) ) 6.1 × 10 -11 exp(-31.6 kJ mol -1 /RT) cm 3 molecule -1 s -1 for 296-922 K. Monitoring growth of Cl during the reaction of phenyl with HCl led to k(C 6 H 5 + HCl) ) 1.14 × 10 -12 exp(+5.2 kJ mol -1 /RT) cm 3 molecule -1 s -1 over 294-748 K, k(C 6 H 5 + DCl) ) 7.7 × 10 -13 exp(+4.9 kJ mol -1 /RT) cm 3 molecule -1 s -1 over 292-546 K, an approximate k(C 6 H 5 + C 6 H 5 I) ) 2 × 10 -11 cm 3 molecule -1 s -1 over 300-750 K, and an upper limit k(Cl + C 6 H 5 I) e 5.3 × 10 -12 exp(+2.8 kJ mol -1 /RT) cm 3 molecule -1 s -1 over 300-750 K. Confidence limits are discussed in the text. Third-law analysis of the equilibrium constant yields the bond dissociation enthalpy D 298 (C 6 H 5 -H) ) 472.1 ( 2.5 kJ mol -1 and thus the enthalpy of formation ∆ f H 298 (C 6 H 5 ) ) 337.0 ( 2.5 kJ mol -1 .

Enthalpy of Formation of the Cyclohexadienyl Radical and the C−H Bond Enthalpy of 1,4-Cyclohexadiene: An Experimental and Computational Re-Evaluation

“…[43][44][45][46] The photochemical reactor is a stainless steel six-way cross heated within an oven. Gas temperatures T in the reaction zone, where the arms of the reactor (i.d. )…”

Kinetic studies of the reaction of atomic chlorine with chlorobenzene

“…Sokolov et al observed no formation of HCl and set an upper limit of k1 < 2.5 x 10 -16 cm 3 molecule -1 s -1 , which agrees with extrapolation of our data. We may also compare k1 with our previous measurements of the analogous reaction 4 [10]. The latter is faster by about a factor of 3 at 700 K and a factor of 2 at 1000 K.…”

“…In these distillations the middle 80% was trapped at 77 K. Details of the apparatus have been given elsewhere [7,10]. Briefly, atomic Cl is formed by pulsed laser photolysis of a small fraction of chlorobenzene at 193 nm.…”

A kinetic study of the reaction of atomic hydrogen with iodobenzene

“…4. The theoretical 0 K reaction enthalpies, combined with H 298 -H 0 values either from the literature [25,27] or computed here (17.9 kJ mol À1 for C 6 H 5 I), yield D r H 298 = À204 and À15 kJ mol À1 for channels (1b) and (1c), respectively. These values are in reasonable agreement with the experimental data given above.…”

“…The invariance of our k 1 data with s res suggests that little dissociation in fact occurred, in part because the initially cold gas flow does not spend all of s res at the temperature of the reaction zone. Any C 6 H 5 produced will be rapidly consumed by reaction with C 6 H 5 I, with a rate constant of about 2 Â 10 À11 cm 3 molecule À1 s À1 [25]. At 900 K and with a typical [C 6 H 5 I] = 4 Â 10 13 molecule cm À3 , a steady state concentration of around 1.5 Â 10 10 molecule cm À3 would be attained, which is too small to perturb the [H] profiles.…”