Hydrogenation of Butadiene Rubber Solutions. II. Influence of the Solvent with Palladium-on-Calcium Carbonate Catalyst

Experiments with allyl alcohol demonstrated the influence of the nature of the solvent on the speed and degree of hydrogenation of an unsaturated organic compound on palladium-on-calcium carbonate catalyst. Butadiene rubber was hydrogenated on palladium-on-calcium carbonate in 2,2-dimethyldioxane-1,5 (DMD), and specimens of hydrorubber insoluble in that solvent were obtained. The same relation between degree of hydrogenation and properties was found for hydrorubber obtained with palladium-on-calcium carbonate catalyst in 2,2-dimethyldioxane-1,5 as had been established for hydrorubber obtained in heptane with the same catalyst : fall in relative viscosity of benzene solutions, lowering of refractive index, and fall in the temperature of vitrification of the rubber with increasing degree of hydrogenation. The selectivity of hydrogenation of the outer double bonds of butadiene rubber when hydrogenated in 2,2-dimethyldioxane is more clearly manifested than in the case of hydrogenation in heptane.

A study of catalytic actions at solid surfaces. Part VII.— The influence of pressure on the rate of hydrogenation of liquids in presence of Nickel

In Parts I, II and V of this series we have indicated the reasons which lead us to believe that during the catalytic hydrogenation of liquids the function of the metallic catalyst is to combine with both agents—the unsaturated organic compound and hydrogen—and produce an unstable intermediate complex. The experimental evidence has furthermore impressed upon us the conviction that the determining factor in hydrogenation is the degree of affinity displayed between nickel and the unsaturated compound; whilst we have had ample opportunity to observe the selective nature of the process as exemplified by the widely-varying rates of absorption of hydrogen characteristic of various definite types of organic compounds, we have not been fortunate enough to obtain experimental proof of the mode in which nickel effects the actual introduction of hydrogen to an organic molecule. We have, therefore, directed our attention to the influence of the concentration of hydrogen on the rate of hydrogenation of liquids, and have examined a wide range of unsaturated organic compounds with respect to the rates at which they absorb hydrogen under varying pressures. Existing data on this subject are scanty, but indicate, in the case of the hydrogenation of fatty oils, that the rate of action is simply proportional to the pressure. On the other hand, it has been suggested that the action of nickel is to adsorb the hydrogen (at the same time dissociating it into the atomic condition) and that it is the atomic hydrogen which interacts with the ethylenic linkage; if this were the case the acceleration induced by increasing the gas-pressure should be proportional to the square root of the latter.

A study of catalytic actions at solid surfaces. II.—The transference of hydrogen from saturated to unsaturated organic compounds in the liquid state in presence of metallic nickel

It has been shown in the first part of this series that hydrogenation in the liquid state at a surface of metallic nickel is to be considered as effected by the temporary union of the unsaturated organic compound and of hydrogen with the nickel, followed by a breakdown of this intermediate system into nickel and the saturated compound. This explanation is a development of the “intermediate compound” theory of catalysis first put forward by De la Rive and differs from the older view mainly in that it postulates an intermediate system of a very loose unstable type, similar to that produced between the natural enzymes, water (or oxygen), and the compounds attacked by the latter, during enzymic catalysis.