A controlled thermal explosion in which methyl isocyanide isomerises quantitatively to methyl cyanide has been studied in a calorimeter at 300 K. The enthalpy of isomerisation ΔH = −23.70 ± 0.14 (2 sdm) kcal mol−1, from which values of the enthalpies of formation of both gaseous and liquid methyl isocyanide are calculated.Similar measurements for ethyl isocyanide yield ΔH = −21.5 ± 1.0 kcal mol−1.

Can. J. Chem. 54,2380(1976. The thermal isomerisation of methyl isocyanide has been measured in the rigorous absence of self-heating over a temperature range from 120-320 "C and at pressures from 2-100 torr. Expressions are given for the rate constant as functions of both temperature and pressure in these ranges of the two variables. The infinite-pressure rate constant is accurately represented by an Arrhenius line with no curvature having E , = 38.2 + 0.2 kcal mol-1 and loglo A , (s-1) = 13.35 + 0.11, although at all other pressures, E is a function of temperature.A number of tests on the cleanliness of the reaction were made, and some previously expressed concerns about side reactions are alleviated considerably. On a effectuC un certain nombre d'essais pour vCrifier la propretC de la reaction; on considere que quelques unes des inquietudes exprimks antkrieurement concernant les rkctions secondaires avaient Ct C grossierement surestimks. JOHN LEWIS COLLISTER et[Traduit par le journal] B Introductiontemperature range was made as wide as possible It has been suggested recently that the explosive isomerisation of methyl isocyanide may prove to be a sensitive and reliable standard against which to test theories of gaseous thermal explosions (1); the required kinetic and thermodynamic data on methyl isocyanide and its iiomerisation are, however, incdmplete for this purpose. As far as the kinetics of the isomerisation are concerned, the rate of the reaction has been studied extensively as a function of pressure at three temperatures only, 200, 230, and 260 OC (2), and extrapolation of these rates into the explosion region (310-360 OC) is very sensitive to small imperfections in the data. The uncertainty of this extrapolation is aggravated by the fact that in some experiments a correction had to be ma8e for self-heating in the reaction, and this correction although small, is itself rather uncertain, giving rise to possible errors in the required extrapolated data. In the work described in this paper, self-heating was eliminated by the appropriate choice of reaction-vessel size for the temperature and pressure in question, and the

The results of measurements of thermal explosions for mixtures of methyl isocyanide with ethyl isocyanide, diethylmercury and di-t-butyl peroxide in spherical vessels near 350 "C are reported. Although the linear mixture rule holds quite well with ethyl isocyanide, it appears to fail mildly for diethylmercury; in the case of di-t-butyl peroxide too much reaction occurs in the inlet to the reaction vessel for a test of the rule to be made. Approximate measurements of the thermal conductivities for ethyl isocyanide and diethylmercury are reported.

Thermal explosions of methyl isocyanide have been studied in spherical reaction vessels with volumes in the range 300–5000 ml. The normal inverse dependence of the explosion limit on the square of the radius appears to hold over limited ranges, e.g. from 300–1000 ml and from 2000–3000 ml, but the explosion limits at 1000 ml and 2000 ml are characterized by markedly different values of the critical parameter δc. Temperature measurements were made at and near the vessel walls, but they do not reveal any abnormalities which could be used to explain these results.An appendix reports measurements of the thermal conductivities of methyl cyanide and methyl isocyanide from 200–350 °C.

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