Gas phase addition of HI to ketene and the kinetics of decomposition of the acetyl radical

Abstract

The addition of HI to ketene results in the rapid formation of acetyl iodide at temperatures 498-525 K. The subsequent slower reaction between HI and acetyl iodide, which produces methane and acetaldehyde has been investigated at low conversions (c 10 %), at various initial pressures at 507 K. The results are shown to be consistent with the mechanism Most experiments were done in the presence of the inert additives N2 or cyclo-C4Fs. (M)+CH3CO + CH3+CO+(M) (5) CH3CO + HI + CH3CHO + I (3) CHs+HI + CH4+I.

Addition of methyl radicals to carbon monoxide: Chemically and thermally activated decomposition of acetyl radicals

“…The A factor for the decomposition of acetyl radicals reported here (1013.2s-1) is very similar to the A factors found for propionyl radical decomposition [7-91 and is essentially the same as that reported by Szirovicza and Walsh [6]. Thus this work supplies additional evidence in favor of a "normal" A factor for acetyl decomposition.…”

“…Thus this work supplies additional evidence in favor of a "normal" A factor for acetyl decomposition. On the other hand the activation energy reported here is significantly lower (by 19 kJ/mole) than that of Szirovicza and Walsh [6]. This difference introduces a disagreement of three orders of magnitude between the two rate constants at 298°K.…”

“…For instance, at low enough temperatures the thermal decomposition of acetyl radicals in reactions (6) and (7) appeared to be negligible compared to reaction (5). The effect of pressure on the formation of acetone and biacetyl was studied at 260,273, and 296"K, where thermal decomposition of acetyl was insignificant.…”

“…Frey and Vinall [5] have studied the pressure dependence of the decomposition of acetyl radicals produced by the photolysis of 3,3-dimethylbutan-2-one at 328°K. They carried out theoretical calculations that showed that the observed pressure dependence was consistent with an A factor of -1012.5 s-l. Szirovicza and Walsh [6] have generated acetyl radicals by the gas phase addition of HI to ketene at 507°K. By a procedure which combines data on the pressure dependence in conjunction with theoretical calculations on the acetyl decomposition reaction the authors estimated that log k,,/(~-') = 13.3-91 (kJ/mole)/2.3 RT O'Neal and Benson's A factor is also strikingly low when compared with three recent measurements of the rate constant for propionyl radical decomposition.…”

Kinetics of the Fully Inhibited Thermal Decomposition of Bistrifluoromethyl Peroxide, CF3OOCF3

“…2). The usefulness of this procedure has been demonstrated in a number of instances (16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Briefly, the procedure consists of showing that if k, in a thermal system is known in the form k, = A, exp (-E,/RT), the microcanonical unimolecular rate constant of specified energy k(E) can be written (neglecting centrifugal effects) where N(E) and N(E -Em) are the densities of states of the reactant molecule at energies E and E -Em, respectively.…”