Kinetics of azobenzene nitrene oxidation by molecular oxygen in glassy propylene carbonate

Abstract

The kinetics of azobenzene nitrene oxidation by molecular oxygen dissolved in a matrix was studied in glassy propylene carbonate. The reaction was carried out in excess oxygen within its concentration range 0.008 to 0.048 M. The oxidation kinetics, controlled by oxygen diffusion, is not described by the exponential function. A specific reaction rate decreases in the course of the process. The higher the oxygen concentration in the matrix, the sharper is the decrease in the reaction rate. It is shown that at all concentrations, the oxidation kinetics is described in the framework of the model of heterogeneous matrix with a characteristic size of heterogeneities of 1.5 nm and a dispersion of the activation energy of oxygen molecule jump of 4 kJ/mol. The reaction radius is about 0.5 nm.

Oxygen Diffusion in Glassy Poly(ethyl methacrylate): Spatial Correlation of Jump Rates

“…Earlier, we proposed a method to determine the spatial distribution of oxygen jump rates in a glassy matrix. , The method has been utilized to measure the jump rates of O 2 in a low-molecular-weight compound, viz., propylene carbonate. Here, we further develop this method and apply it to the diffusion of O 2 in PEMA.…”

“…In the latter case, a polymer film saturated with oxygen, with a content of aryl-azide (ArN 3 ) of ≈ 0.01 M, was irradiated with 365 nm light from a high-pressure mercury lamp to convert aryl-azide into aryl-nitrene in the triplet ground state. The experimental methods have been previously described in detail. , Molecular oxygen encounters the generated particles and quenches phenanthrene or forms an oxidation product The oxygen content was set to be much higher than that of C 14 H 10 and ArN 3 , but the average distance between these molecules and oxygen was greater than the respective reaction radius, ρ, to ensure that the reactions are controlled by diffusion. The reactions are considered to proceed “instantly” as soon as the distance between (C 14 H 10 )* or ArN̈ and O 2 decreases to ρ.…”

“…The values of ρ for processes () and () differ considerably and amount to 1 and 0.5 nm, respectively. ,, As a consequence, the kinetics of these processes differ strongly. A successful fit of such different processes using the same diffusion model considerably increases the reliability of this model and the obtained parameters.…”