Thermal reaction of 2-methyl-2-butene in the presence of azomethane: enthalpy of formation of the radicals (CH3)2ĊCH(CH3)2 and tert-Ċ4H9

Abstract

The reaction of ĊH₃ and 2-methyl-2-butene (2MB2) was investigated in the temperature range 540610 K. Azomethane was used as the source of ĊH₃. The addition of ĊH₃ to 2MB2 was concluded to be an equilibrium process: ĊH₃+(CH₃)₂C2CHCH₃(CH₃)₂ĊCH(CH₃)₂. The equilibrium constant of this reaction was determined from the rates of formation of the combination products (E)- and (Z)-CH₃CH₂C(CH₃)2CHCH₃ and (E)- and (Z)-(CH₃)₂CHC(CH₃)₂CH₂C(CH₃)2CHCH₃. Finally, the enthalpy of formation of the adduct radical, Δ_fH₂₉₈^°[(CH₃)₂ĊCH(CH₃)₂] = (3±10) kJ mol⁻¹, was obtained from the temperature dependence of the equilibrium constant. On the assumption that the group additivity rule was valid for the adduct radical, the following group value was obtained: Δ_fH₂₉₈^°[Ċ–(C)₃] = (179±12) kJ mol⁻¹. Through use of this datum Δ_fH₂₉₈^°(tert-Ċ₄H₉) = (53±12) kJ mol⁻¹.