Kinetics of Combustion of Cyanogen and the Burning Velocities of Cyanogen-Oxygen-Nitrogen Mixtures

Abstract

Kinetics of Combustion of Cyanogen 1891 runs with excess C6Cle do not produce even a transient formation of the blackish copper-containing precipitate, again arguing that reaction 1 must be a rapid equilibration which ties up an appreciable portion of the Cu(I). But if reaction 4 were ratedetermining, two other problems would appear. The over-all rate would be proportional to the square of the concentration of the less abundant reactant, which is contrary to the experimental data. Furthermore, the observed pre-exponential factor is very large for the formation of an oriented transition state involving two complex molecules.On the other hand, the Ea of 13.7 kcal. and the large pre-exponential factor seem appropriate to the monomolecular decomposition of the CeCle-CuCl complex (reaction 2). For this mechanism, with rapid complex equilibration and K\ of moderate size (say, between 1 and 25 1. mole-1), the overall observed dependency would be essentially first order (with respect to the less abundant reactant) at reactant concentrations of about 1M and greater, and essentially second order (first order with respect to each reactant) at reactant concentrations of the order of 0.1 M and less. This latter case conforms to our observations, both of the kinetics and of the unusual stoichiometry of the reaction. Finally, the reacting system of CeCU and CuCl rapidly decolorizes diphenylpicrylhydrazyl, while in the absence of either reactant the color is comparatively stable (it is slowly discharged by CuCl alone). This is strong evidence for radical intermediation. In view of this, the failure of the reacting system to initiate styrene polymerization may be ascribed to the extremely high stability, due to resonance and symmetry, of the CbCIb• radical. This radical is too inert to initiate vinyl polymerization; its stability limits it to reactions with other radicals (e.g., other C6C16• radicals and diphenylpicrylhydrazyl).