The decomposition of 2,2,3,3-tetramethylbutane in KCl- and B2O3-coated vessels in the presence of oxygen

Abstract

The decomposition of 2,2,3,3-tetramethylbutane (TMB) in the presence of oxygen has been studied in both KCl-coated and aged boric-acid-coated vessels. The values for k₁ obtained with the two types of vessel surface are in close agreement, and combination of the values over the range 400–542 °C gives A₁= 1.04 × 10¹⁷ s^–1, E₁= 294.7 ± 3 kJ mol^–1, effectively identical with previous values using KCl-coated vessels, and thus confirming the thermochemistry suggested for the t-butyl radical: (CH₃)₃C—C(CH₃)₃→ 2(CH₃)₃C. (1) The observed rate constant, k_obs, defined by the equation –d [TMB]/dt=k_obs[TMB] increases with increasing TMB concentration with both types of vessel surface and this variation has been used to evaluate the ratio k₄/k₇^½. The results with both types of vessel surface are in agreement, giving A₄/A₇^½= 4.4 × 10⁵(dm³ mol^–1 s^–1)^½, E₄–½E₇= 81.7 ± 8 kJ mol^–1 over the range 400–520 °C: HO₂+(CH₃)₃C—C(CH₃)₃→ H₂O₂+(CH₃)₃C → C(CH₃)₂CH₂(4) HO₂+ HO₂→ H₂O₂+ O₂. (7)