Addition of 2,3-dimethylbutane to slowly reacting mixtures of hydrogen and oxygen at 480 °C. Rate constants of the elementary reactions involved

Abstract

The oxidation of 2,3-dimethylbutane (DMB) has been studied by adding traces of the alkane to slowly reacting H₂–O₂ mixtures in an aged boric acid coated vessel at 480 °C. Rate constants have been obtained for H and HO₂ attack on DMB, and Arrhenius parameters of log₁₀(A/dm³ mol^–1 s^–1)= 9.45 (per C—H bond) and E= 67 kJ mol^–1 are suggested for HO₂ attack at the tertiary C—H bond in DMB. Combination with data at room temperature gives log₁₀(A₂₂/dm³ mol^–1 s^–1)= 11.45 and E₂₂= 30 kJ mol^–1 for the overall reaction H + DMB → H₂+ C₆H₁₃. (22)

Methane, propene, 2,3-dimethylbut-1-ene, 2,3-dimethylbut-2-ene, 2-methylbut-2-ene, and the two O-heterocyclic compounds, 2,2,3-trimethyl-oxetane and tetramethyloxirane, are the major initial products. The proportions of the two species of dimethylbutyl radicals formed in each mixture used has been estimated by computer treatment in order to facilitate interpretation of the product distribution. Detailed mechanisms for the two radicals are discussed quantitatively. Rate constants are determined for the 1,4t H atom transfer involved in reaction (5A) and for the 1,5t transfer involved in reaction (5B). No other experimentally derived value is available for a 1,5t H atom transfer in alkylperoxy radicals (CH₃)₂C(O₂)CH(CH₃)₂→(CH₃)₂C(O₂H)C(CH₃)₂(5A), (CH₃)₂CHCH(CH₃)CH₂O₂→(CH₃)₂CCH(CH₃)CH₂O₂H. (5B)

The role of reaction (X) in the mechanism of autoignition of alkanes is discussed R + O₂→ conjugate alkene + HO₂. (X)