Radical equilibrium studies. II. The thermodynamic parameters of s−butyl

The thermal decomposition of azomethane in the presence of propene has been investigated in the range of 568–638°K at reactant partial pressures of up to about 7 torr in the presence of at least 170 torr of argon. The elementary reactions taking place in such conditions are discussed in detail. It is shown that a situation approaching equilibrium is attained between the processes equation image Values are obtained for the equilibrium constant K2, which can be described by the equation Using the best available thermodynamic parameters for methyl and propene, it is concluded that those for s−butyl are in need of adjustment. We recommend the values ΔHf0 (300°K) = 13.8 ± 1.0 kcal/mol and S3000 (1 atm standard state) = 75.6 ± 3.0 cal/mol°K together with group additivity values of the heat capacity. A comparison of measured values of K2 with values calculated from independent measurements of k2 and k−2 shows a discrepancy of about a factor of 3.5.