Homogeneous reactions involving complex molecules.—The kinetics of the decomposition of gaseous dimethyl ether

Chemical changes in which molecules of complex structure take part have recently assumed a particular importance in the theory of the mechanism of reaction velocity. Decompositions of organic compounds in the gaseous state provide excellent examples of such reactions. It is often necessary, in these, to suppose the intermediate formation of unstable radicles which undergo rapid subsequent transformations; and whenever each stage of a reaction is not expressed by conventional chemical equations, involving known substances only, there may always remain a slight doubt whether the course of the reaction has been truly represented. Although this does not prevent the drawing of perfectly valid conclusions about the kinetics of a given reaction, nevertheless an example in which every stage can be represented by a simple chemical equation has undoubted advantages. The decomposition of dimethyl ether, with which this paper deals, provides such an example. CH 3 .O.CH 3 → [CH 4 + HCHO] → CH 4 + H 2 + CO. The complexity of the dimethyl ether molecule is only moderate, and in the light of the discussion in the papers referred to above it is interesting to note that the reaction is an almost perfect example of the transition from the unimolecular to the bimolecular type.