AbstractThe thermal reaction of hydrogen–butene‐2‐cismixtures has been studied in a static system at low extent of reaction around 500°C. Hydrogen does not affect the thermal reaction itself of the olefin, but gives rise to new stoichiometries of hydrogenolysis and hydrogenation, which are specified:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm H}_2 + cis - 2 - {\rm C}_4 {\rm H}_8 = {\rm CH}_4 + {\rm C}_3 {\rm H}_6 \\ {\rm H}_2 + cis - 2 - {\rm C}_4 {\rm H}_8 = {\rm H}_2 + 1 - {\rm C}_4 {\rm H}_8 \\{\rm H}_2 + cis - 2 - {\rm C}_4 {\rm H}_8 = n - {\rm C}_4 {\rm H}_{10} \\ \end{array} $$\end{document}The reaction is described in terms of a molecular and free‐radical mechanism. It is shown that the key process for the hydrogenolysis–hydrogenation reaction isand that the rate constant of this process can be determined from either propylene, or methane, or butene‐1 formations:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k}_{{\rm 7'}} \simeq {\rm 10}^{{\rm 13}{\rm .1 - 24}{\rm .2/}\theta } \,{\rm cm}^{\rm 3} {\rm /mol} \cdot {\rm s} $$\end{document}with θ = 4.57 × 10−3Tkcal/mol. Other rate constants are estimated and agree with