## Abstract

Chloroform and the other chloromethanes, except carbon tetrachloride, accelerate the gas-phase oxidation of propane in the `low-temperature' region. The relation of pressure change to reactant consumption and final product formation is not significantly modified in the catalyzed reaction, which can still be followed by pressure measurements. The value of the maximum rate in the presence of chloroform is given fairly closely by the expression $\frac{(\rho_{max.})_{[CHCL_3]}}{(\rho_{max.})_0} = 1 + \frac{constant x [CHCl_3]}{[RH]}.$ The form of this suggests that, in the rate-determining steps, chloroform and paraffin are involved in analogous processes, and the key step is postulated to be $\mathrm{RO}_2\cdot + \mathrm{CHCl}_3 \rightarrow \mathrm{ROOH} + \mathrm{CCl}_3\cdot$ which re-inforces the reaction $\mathrm{RO}_2\cdot + \mathrm{RH} \rightarrow \mathrm{ROOH} + \mathrm{R}\cdot$ in competing with those steps normally leading to degradation of RO$_2\cdot$ radicals. Since little or no isotopic exchange occurs when CDCl$_3$ is used in place of CHCl$_3$, the radical CCl$_3\cdot$ does not regenerate chloroform, but initiates chains of the type $\mathrm{CCl}_3\cdot \rightarrow \cdot\mathrm{CCl}_2\cdot + \mathrm{Cl}\cdot, \\ \mathrm{Cl}\cdot + \mathrm{RH} \rightarrow \mathrm{HCl} + R\cdot.$ A slow consumption of chloroform (the oxidation of which is unimportant in the absence of propane) occurs, together with a slow build-up of hydrogen chloride. With certain approximations, a simple chain mechanism reproduces the experimental kinetic formula.