Pressure-dependence of the gas-phase pyrolysis of the s-butoxyl radical at 150–190°

Abstract

The pressure-dependence of the gas-phase pyrolysis of the s-butoxyl radical, giving the ethyl radical and acetaldehyde, has been studied by comparing the rate with that of the disproportionation between the radical and nitric oxide, giving ethyl methyl ketone and nitroxyl, in the early stages of the pyrolysis of 1 : 1 s-butyl nitrite–nitric oxide mixtures at 150–190° and 12–200 mm. total pressure. The pyrolysis of the radical is in the transition zone between first- and second-order; the pseudo-first-order rate constant is half its high-pressure value at 110 mm./190°. Limiting high- and low-pressure rate constants give E_∞= 17·5 and E₀= 10·6 kcal. mole^–1, corresponding to 17 Slater or 9·5 Kassel oscillators effective in energy transfer, and A_∞= 2·5 × 10¹³ sec.^–1 and A₀= 3·2 × 10¹⁴ mole^–1 cm.³ sec.^–1. The efficiency of a wide range of additives in energy transfer has been examined; the trends with molecular complexity are as expected but the efficiencies are lower than found for the isopropoxyl radical. The rate-constant for abstraction of hydrogen from s-butyl nitrite by the s-butoxyl radical is given by k_s= 4 × 10¹¹ exp –(3900/RT) cm.³ sec^–1.