Abstract
The thermal decomposition of cyclopentyl cyanide has been investigated in the temperature range of 905โ1143 K using both conventional stirredโflow reactor and very lowโpressure pyrolysis (VLPP) techniques. The results from both techniques are consistent. The main primary processes are HCN elimination to form cyclopentene:
equation image
and ring fragmentation to form vinyl cyanide plus propylene and ethylene plus cyanopropenes:
equation image
Under the experimental conditions cyclopentene undergoes further decomposition to cyclopentadiene plus hydrogen. There is evidence for conversion of some of the reactant to a solid residue, presumably polymer. From the stirredโflow reactor results the following Arrhenius expressions were obtained: log k~1~(s^โ1^) = (12.8 ยฑ 0.3) โ (65.6 ยฑ 1.3)/ฮธ and log k~2~(s^โ1^) = (16.0 ยฑ 0.3) โ (80.0 ยฑ 1.1)/ฮธ, where ฮธ = 2.303__RT__ kcal/mol. Application of RRKM theory shows that the VLPP experimental rate constants are consistent with highโpressure Arrhenius parameters given by log k~1~(s^โ1^) = (12.8 ยฑ 0.3) โ (67.8 ยฑ 2.5)/ฮธ for HCN elimination, and log k~4~(s^โ1^) = (16.3 ยฑ 0.3) โ (80.1 ยฑ 2.0)/ฮธ for the sum of the ring fragmentation pathways. The rate parameters for HCN elimination are in good agreement with previous VLPP studies of alkyl cyanides and with theoretical predictions. The difference in activation energies for the ring opening of cyclopentane and cyclopentyl cyanide is reasonably close to the established value for the cyano stabilization energy. This supports the assumption of a biradical mechanism.