The homogeneous catalysis of gaseous reactions by iodine. The decomposition of propionic aldehyde, and a general discussion

Previous papers have dealt with the homogeneous catalysis of the decomposition of ethers and of acetaldehyde by iodine. The problem of the mechanism of these catalysed reactions can be approached in two ways: on the one hand, by seeking to obtain as complete a picture as possible of the types of chemical change which are susceptible to the action of a given catalyst, and, the catalysts which will promote a given chemical change; and, on the other hand, by investigating in detail the kinetics and molecular statistics of individual reactions. Experiments on the different kinds of reaction which iodine will catalyse are being published elsewhere. Most of the chemical changes have involved too many side reactions, or secondary reactions with the catalyst, to be suitable for complete kinetic analysis. Nevertheless, they show the chemical specificity of the action of iodine in the clearest manner, and this aspect of the problem is discussed from a general point of view in the last section of the present paper.