Thermal isomerization of ethylidenecyclopropane and methylmethylenecyclopropane to 2-methylbuta-1,3-diene

Abstract

The thermal isomerization of an equilibrium mixture of ethylidenecyclopropane and methylmethylenecyclopropane to isoprene is a unimolecular reaction obeying the Arrhenius equation log k/s^–1= 13.212 ± 0.144 –(223.9 ± 1.9 kJ mol^–1)/RT ln 10, in the temperature range 395 to 450°C.

The mechanism of this reaction is discussed and a complex suggested involving a 1,4 hydrogen shift. Its relation to isomerizations reported for cyclobutanes is considered.