The azoethane-initiated thermal reaction of isobutene. Heat of formation of the 2-methyl-2-pentyl radical

The azoethane-sensitized thermal reaction of isobutene has been studied at 526–565 K. The initial concentrations of azoethane and isobutene were in the ranges of 1.40–10.5 × 10^?4 and 6.78–26.6 × 10^?4 mol/dm³, respectively. From the initial rates of formation of ethane and 2-methylpentane the heat of formation of the 2-methyl-2-pentyl radical was determined. The result obtained is ±H(2-methyl-2-pentyl) = 0.8 ± 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S⁰(2-methyl-2 pentyl) = 92.8 ± 1.5 cal/mol°K. The results support the high heat of formation of the t-butyl radical suggested by different authors.