Thermal isomerization of cyclobutenes. Part 18.—1-Chlorocyclobutene and 1-bromocyclobutene

The thermal isomerization of 1-chlorocyclobutene yielded 2-chlorobuta-1,3-diene quantitatively by a homogeneous first-order reaction. In the temperature range 423–473 K and at pressures of 1 kN m–2 and above, rate constants were determined and yielded the Arrhenius equation, log (k1/s–1)= 13.26±0.03–140 750±270 J mol–1/2.303 RT. At pressures below 150 N m–2 the rate constant decreased with decreasing pressure. The thermal isomerization of 1-bromocyclobutene yielded 2-bromobuta-1,3-diene. This reaction was homogeneous and first order at pressures above 1 kN m–2. In this pressure region, rate constants were determined at 10 temperatures in the range 424–458 K. The rate constants fitted the Arrhenius equation, log (k2/s–1)= 13.53±0.06–141 270±510 J mol–1/2.303 RT. At 446.6 K the rate constant was determined at various pressures in the range 1.26 kN m–2–1.18 N m–2. The “fall-off” curve so obtained was compared with those obtained by the application of the RRKM theory.