Decomposition of 2,2,3-trimethylbutane in the presence of oxygen

Abstract

The decomposition of 2,2,3-trimethylbutane in the presence of O₂ in KCl-coated vessels has been studied at 480 and 500 °C over the pressure range 60–500 Torr. At low alkane pressures, where the chain contribution is small, the results are consistent with a simple mechanism comprising reactions (10), (11), (2) and (3). (CH₃)₃CCH(CH₃)₂→ t-C₄H₉+i-C₃H₇(10), i-C₃H₇+O₂→ C₃H₆+HO₂(11), t-C₄H₉+O₂→ i-C₄H₈+HO₂(2), HO₂ [graphic omitted] ½H₂O+¾O₂(3), From measurements of the i-butene yields, accurate rate constants may be obtained for reaction (10) which, when combined with Tsang's results, give log₁₀(A₁₀/s^–1)= 16.46 ± 0.12 and E₁₀= 305.0 ± 1.5 kJ mol^–1 over the temperature range 480–925 °C. Following a discussion of the thermo-chemistry of reaction (10) and the value of k_–10, values of Δ_fH^°₂₉₈(t-Bu)= 37.6 ± 2.0 and Δ_fH^°₂₉₈(i-Pr)= 80.8 ± 4.0 kJ mol^–1 are recommended, which correspond to D^°₂₉₈(t-Bu—H)= 390.2 ± 2.0 and D^°₂₉₈(i-Pr—H)= 402.5 ± 4.0 kJ mol^–1, respectively.

Two of the three species of radicals formed by radical attack on 2,2,3-trimethylbutane appear to react solely by C—C homolysis of the central C—C bond. The third radical, (CH₃)₃CC(CH₃)₂, reacts mainly by homolysis, but also forms the minor initial products 2,3,3-trimethylbut-1-ene, acetone and 2,3-dimethylbut-2-ene. A value of k₁₇= 1.4 × 10³ s^–1 at 480 °C has been obtained. (CH₃)₃CC(CH₃)₂→(CH₃)₂CC(CH₃)₂+CH₃(17).