Kinetics and mechanism of the thermal decomposition of ethyl cyanide

Abstract

The pyrolysis of ethyl cyanide in the presence and absence of radical-chain inhibitors has been investigated in the temperature range 896-1020 K using a stirred-flow reactor at atmospheric pressure with nitrogen as the carrier gas. In the absence of additives the decomposition proceeds by a homogeneous free-radical chain process to yield HCN, C2H4, H2, and C2H3CN as major products. On the assumption of first-order kinetics rate constants for the overall reactions C2H6CN -* HCN + C2H4 (3) and C2H5CN --H2 + C2H3CN (4) are given by the Arrhenius expressions log (k3/s_1) = (14.3 ± 0.4) -(283.7 ± 6.7) kJ mol_1/2.3RT and log (k4/s_1) = (12.1 ± 0.3) -(247.3 ± 5.9) kJ moT1/2.3ñT. Some aspects of a radical-chain mechanism are discussed. Addition of large amounts of PhNH2 or PhCH3 relative to ethyl cyanide completely suppresses the overall reactions 3 and 4 and the mechanism of ethyl cyanide decomposition becomes C2H5CN -*• CH3 + CH2CN (1), CH3 + RH -* CH4 + R, CH2CN + RH -CH3CN + R where RH is PhNH2 or PhCH3. In the presence of excess PhNH2 the first-order rate constants for CH3CN formation, which are indicative of the unimolecular C-C bond fission reaction 1, are reasonably consistent with the Arrhenius expression log (fei/s-1) = 15.25 -338.9 kJ mol~1/2.3RT. The results are in good agreement with predictions based on the very low-pressure pyrolysis (VLPP) of alkyl cyanides and provide further confirmation that the stabilization energy of the cyanomethyl radical is =¿21 kJ mol'1.

Thermal decomposition of acetonitrile. Kinetic modeling

“…The reason for not observing a sharp decrease of the rate in the experiment is unclear. The same analysis is true also for propyl nitrile [9] (Fig. 8).…”

CryptoCope Rearrangement of 1,3-Dicyano-5-phenyl-4,4-d2-hexa-2,5-diene. Chameleonic or Centauric?

“…−14 kcal mol -1 vis-à-vis hydron. , Confusion has surrounded the heat of formation even of acetonitrile. Its value of 15.4 kcal mol -1 , accepted by Pedley et al, has been revised drastically to 17.8 kcal mol -1 by An and Månsson, and Barnes and Pilcher in 1983, although this change had already been forewarned in 1975 by King and Goddard,27a and recognized without discussion by Lias et al Significant revisions to the basic enthalpies of formation of 2° and 3° aliphatic radicals have also appeared, largely owing to the efforts of the late David Gutmann and co-workers …”