Butyl iodide, pyrolysis

Recent electron impact work by Stevenson leads to D(n-04X49 X4) =4 33 0-1 eV, or 101 kcal. This is much higher than the not very reliable result of 94 kcal obtained from the pyrolysis of w-butyl iodide. 

We may use the observations listed above to derive in some cases the temperature coefficients of the rate of pyrolysis and hence the activation energy of the reaction. For w-propyl iodide and n-butyl iodide we have sufficiently reliable data for two temperatures from which we calculate for -propyl 0 = 52 kcal. and for -butyl Q = 53 kcal. This lends support to the value of similar magnitude, Q — 55 kcal., obtained from the otherwise less reliable Exps. 3, 4, and 6, 7, 8 for ethyl iodide. 

Finally we add some observations on acetonyl iodide and methyl iodide. We had considerable difficulty with the former substance on account of the decomposition which it undergoes by light and even on standing. Yet Table I (7) may reasonably indicate the position of this compound among other iodides. It lies between benzoyl and -butyl, so that -butyl < acetonyl < benzoyl roughly in the ratio 1 4 70. While methyl iodide gave no reproducible results, its pyrolysis proved very distinctly slower than that of ethyl iodide. The mean rate constant 4 2 X 10- sec. is about 3 times less than that of ethyl iodide. 

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