ChemInform Abstract: KINETICS AND MECHANISM OF THE THERMAL DECOMPOSITION OF CYCLOPENTYL CYANIDE

Abstract

The thermal decomposition of cyclopentyl cyanide has been investigated in the temperature range of 905–1143 K using both conventional stirred-flow reactor and very low-pressure pyrolysis (VLPP) techniques. The results from both techniques are consistent. The main primary processes are HCN elimination to form cyclopentene: and ring fragmentation to form vinyl cyanide plus propylene and ethylene plus cyanopropenes: 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 stirred-flow reactor results the following Arrhenius expressions were obtained: log k1(s−1) = (12.8 ± 0.3) − (65.6 ± 1.3)/θ and log k2(s−1) = (16.0 ± 0.3) − (80.0 ± 1.1)/θ, where θ = 2.303RT kcal/mol. Application of RRKM theory shows that the VLPP experimental rate constants are consistent with high-pressure Arrhenius parameters given by log k1(s−1) = (12.8 ± 0.3) − (67.8 ± 2.5)/θ for HCN elimination, and log k4(s−1) = (16.3 ± 0.3) − (80.1 ± 2.0)/θ 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.