## Abstract

In the presence of nitric oxide the decomposition of gaseous tertiary butyl peroxide has been shown to follow essentially the course: $ \matrix\format\l \\ (\text{i})\ (\text{CH}_{3})_{3}\text{COOC}(\text{CH}_{3})_{3}@>k_{1}>>2(\text{CH}_{3})_{3}\text{CO}, \\ (\text{ii})\ (\text{CH}_{3})_{3}\text{CO}\quad \quad \ \quad \quad @>k_{2}>>(\text{CH}_{3})_{2}\text{CO}+\text{CH}_{3}, \\ (\text{iii})\ 2\text{CH}_{3}\quad \quad \quad \quad \quad \ \quad @>k_{3}>>\text{C}_{2}\text{H}_{6}, \\ (\text{iv})\ (\text{CH}_{3})_{3}\text{CO}+\text{NO}\ \,\quad @>k_{4}>>(\text{CH}_{3})_{3}\text{CONO}, \\ (\text{v})\ \text{CH}_{3}+\text{NO}\quad \quad \quad \quad \ \ @>k_{5}>>\text{CH}_{3}\text{NO}@>>>\text{other products.} \endmatrix $ Rates of reaction have been measured by observation of pressure changes and mass-spectrometric analysis for peroxide, acetone, ethane, nitric oxide and tertiary butyl nitrite at various stages. The ratio k$_{4}$/k$_{2}$ at 160 degrees C, determined from the rate of formation of acetone in presence of nitric oxide, is approximztely 0$\cdot $7 (with concentrations expressed in mm Hg). If the 'collision yield' or 'steric factor' for the union of methyl radicals is near unity, that for the combination of methyl radicals and nitric oxide is about 7 $\times $ 10$^{-5}$, from experiments on the rate of ethane formation. If the rate constants for the combination of nitric oxide with methyl and tertiary butoxy radicals respectively are assumed equal, k$_{2}$ is estimated to be about 10$^{3}$s$^{-1}$ at 160 degrees C. A rough estimate for the corresponding activation energy (E$_{2}$) gives 13$\cdot $2 $\pm $ 2$\cdot $4 kcal/mole for the decomposition of the tertiary butoxy radical, compared with a (redetermined) value of 38 kcal/mole for that of the peroxide itself.