The Polymerization of Gaseous Butadiene

Dimerization of butadiene has been studied in the temperature range from 446 to 660°K. The rate constant is expressed approximately by the equation: $$k_2{\text{=9.20·10}}^9\hspace{0.17em}\exp \text{\hspace{0.17em}(−23,690/RT)\hspace{0.17em}}\mathrm{cc}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}\sec {.}^{\text{−1}}.$$ Deviations from this relation suggest an increase of activation energy with temperature. 3‐vinyl cyclohexene formed in the dimerization reaction undergoes further addition with butadiene to give Δ3,3′‐octahydro diphenyl. The rate constant of this reaction is given by the equation: $$k_3{\text{=1.3·10}}^{14}\hspace{0.17em}\exp \text{\hspace{0.17em}(−38,000/RT)\hspace{0.17em}}\mathrm{cc}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}\sec {.}^{\text{−1}},$$ but the data on which it is based are not very accurate. Statistical calculation of the entropy of an activated complex which has the resonating structure $${\mathrm{H}}_2\mathrm{C}{{\displaystyle {lim}^{⋮}}}_{\mathrm{...}}^{-}{\mathrm{CH}}_{\mathrm{...}}^{-}\mathrm{C}{\displaystyle {lim}^{⋮}}\mathrm{H}–{\mathrm{CH}}_2–{\mathrm{CH}}_2–\mathrm{C}{\displaystyle {lim}^{⋮}}{\mathrm{H}}_{\mathrm{...}}^{-}{\mathrm{CH}}_{\mathrm{...}}^{-}\mathrm{C}{\displaystyle {lim}^{⋮}}{\mathrm{H}}_2$$ gives agreement with experimental data to within a factor of ten whereas the assumption that the reaction goes in a single step to the cyclic product gives a rate differing by more than a thousand‐fold from the observed one. The role of resonating free radicals in other reactions of the dienes is discussed briefly.