Kinetics of the Thermal Decomposition of Di-t-Butyl Peroxide

Abstract

The kinetics of the thermal decomposition of di‐t‐butyl peroxide were studied in the presence of excess toluene using a static and a flow system, the temperature range being 120° to 280°C. The decomposition was represented by the following mechanism: $$\begin{array}{c}({\mathrm{CH}}_3{)}_3\mathrm{C}.\mathrm{O}.\mathrm{O}.\mathrm{C}({\mathrm{CH}}_3{)}_3\text{→2(}{\mathrm{CH}}_3{)}_3.\mathrm{CO}·\\ ({\mathrm{CH}}_3{)}_3.\mathrm{CO}\mathrm{·\to }{\mathrm{CH}}_3\mathrm{·+}{\mathrm{CH}}_3.\mathrm{CO}.{\mathrm{CH}}_3\\ \text{\hspace{0.17em}\hspace{0.17em}2}{\mathrm{CH}}_3\mathrm{·\to }{\mathrm{C}}_2{\mathrm{H}}_6\\ {\mathrm{CH}}_3\mathrm{·+}{\mathrm{C}}_6{\mathrm{H}}_5.{\mathrm{CH}}_3\to {\mathrm{CH}}_4+{\mathrm{C}}_6{\mathrm{H}}_5.{\mathrm{CH}}_2·\\ {\mathrm{CH}}_3\mathrm{·+}{\mathrm{C}}_6{\mathrm{H}}_5.{\mathrm{CH}}_2\mathrm{·\to }{\mathrm{C}}_6{\mathrm{H}}_5.{\mathrm{CH}}_2.{\mathrm{CH}}_3\end{array}$$ The rate of reaction was measured by the rate of formation of CH₄+C₂H₆. It was shown that the decomposition is a homogeneous gas reaction of the first order. The activation energy seems to be 36±1 kcal/mole, corresponding to the frequency factor of the order 4.10¹⁴−7.10¹⁴ sec⁻¹. It was shown that the rate of reaction is not influenced by the pressure of toluene and by the toluene/peroxide ratio. It remains the same even in the extreme case when no toluene is present, or when benzene is used instead of toluene. The rates of decomposition obtained in this study are in fair agreement with the rates obtained for the same reaction by Rust and Vaughan. The following values have been obtained for dissociation energies: $$\begin{array}{c}\mathrm{D}\mathrm{[(}{\mathrm{CH}}_3{)}_3.\mathrm{CO}–\mathrm{OC}\mathrm{.\; (}{\mathrm{CH}}_3{)}_3\text{]=36\hspace{0.17em}}\mathrm{kcal/mole}\\ \mathrm{D}\mathrm{[(}{\mathrm{CH}}_3{)}_3.\mathrm{CO}–\mathrm{H}\text{]=106\hspace{0.17em}}\mathrm{kcal/mole}\\ \mathrm{D}\mathrm{[(}{\mathrm{CH}}_3{)}_3·\mathrm{CO}–\mathrm{OH}\text{]=39\hspace{0.17em}}\mathrm{kcal/mole}\end{array}$$ and the heat of formation of (CH₃)₃.CO· radical has been estimated at −23 kcal/mole.