High-temperature reactions and thermodynamic properties of phenyl radicals

Abstract

Reactions of phenyl radicals were studied in reflected shock waves in the temperature range 1050–1450 K using UV absorption spectroscopy. Rate constants for the following reactions were derived: 2 C 6 H 5 → C 12 H 10 ( k 1 =5.7×10 12 cm 3 mol −1 s −1 ), C 6 H 5 +H 2 →C 6 H 6 +H ( k 3 =10 12.6 exp(−33 kJ mol −1 / RT ) cm 3 mol −1 s −1 ): C 6 H 5 +C 6 H 5 CH 3 →C 6 H 6 +C 6 H 5 CH 2 ( k 4 =10 13.9 exp(−50 kJ mol −1 / RT ) cm 3 mol −1 s −1 ), C 6 H 5 +CH 4 →C 6 H 6 +CH 3 ( k 5 =10 12.3 exp(−36 kJ mol −1 / RT ) cm 3 mol −1 s −1 ), and C 6 H 5 +C 2 H 2 →C 6 H 5 C 2 H+H ( k 8 =10 13.0 exp(−32 kJ mol −1 / RT ) cm 3 mol −1 s −1 ). Phenyl iodide dissociation equilibrium was also investigated. In combination with results from other laboratories, equilibrium constants for five different equilibria involving phenyl radicals were determined. A third-law analysis of these data leads to an enthalpy of formation of phenyl radicals of ΔH f 298 o =(338±3) kJ mol −1 .