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

The laser flash photolysis resonance fluorescence technique was used to monitor atomic Cl kinetics. Loss of Cl following photolysis of CCl4 and NaCl was used to determine k(Cl + C6H6) = 6.4 × 10-12 exp(−18.1 kJ mol-1/RT) cm3 molecule-1 s-1 over 578−922 K and k(Cl + C6D6) = 6.2 × 10-12 exp(−22.8 kJ mol-1/RT) cm3 molecule-1 s-1 over 635−922 K. Inclusion of literature data at room temperature leads to a recommendation of k(Cl + C6H6) = 6.1 × 10-11 exp(−31.6 kJ mol-1/RT) cm3 molecule-1 s-1 for 296−922 K. Monitoring growth of Cl during the reaction of phenyl with HCl led to k(C6H5 + HCl) = 1.14 × 10-12 exp(+5.2 kJ mol-1/RT) cm3 molecule-1 s-1 over 294−748 K, k(C6H5 + DCl) = 7.7 × 10-13 exp(+4.9 kJ mol-1/RT) cm3 molecule-1 s-1 over 292−546 K, an approximate k(C6H5 + C6H5I) = 2 × 10-11 cm3 molecule-1 s-1 over 300−750 K, and an upper limit k(Cl + C6H5I) ≤ 5.3 × 10-12 exp(+2.8 kJ mol-1/RT) cm3 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(C6H5−H) = 472.1 ± 2.5 kJ mol-1 and thus the enthalpy of formation Δf H 298(C6H5) = 337.0 ± 2.5 kJ mol-1.