Eric K. Rideal

On the catalytic cyclization of aliphatic hydrocarbons. I

The aromatization of a paraffin proceeds through the formation of a mono-olefine which is held on the catalyst by two-point contact. The promoter action of the central atoms in heteropoly acids of molybdenum can be attributed to the stabilization of the molybdenum dioxide produced during the hydrogen pretreatment. The alumina used as a support for molybdenum catalysts plays the same role. In the reduction of phenol to benzene by the heteropoly acids of molybdenum the metal is the catalyst. The variation of yield of the total aromatic hydrocarbon with different paraffin feeds can be calculated by assuming two point contact. A yellow compound (fulvene or a polymer of fulvene) is for given conditions produced in a constant ratio to the aromatic hydrocarbon. The loss of activity of the catalyst with use is a result of the polymerization to giant molecules of the hydrocarbons adsorbed on adjacent catalyst centres. This decay rate may be diminished by decreasing the concentration of active centres on the surface.

The Oxidation of Liquid Hydrocarbons. I. The Chain Formation of Hydroperoxides and Their Decomposition

The course of the low-temperature liquid-phase oxidation of hydrocarbons through hydroperoxide formation and subsequent decomposition has been confirmed. The function of a heavy metal catalyst is to increase both the rate of formation and decomposition of this hydroperoxide. The dependence of the stationary concentration of hydroperoxide on the oxidation rate and the catalyst concentration indicated that the hydroperoxide decomposition is unimolecular with the reaction velocity constant directly proportional to the catalyst concentration. This has been confirmed by independent decomposition experiments. It is suggested that the reaction involves the breakdown of a ‘heavy metal catalyst-hydroperoxide’ complex. From a study of the oxidation rates of hydrocarbons, alcohols and ketones, and the oxidation of mixtures, it was found that alcohols are the most resistant to oxidative attack and furthermore inhibit the catalysed oxidation of long-chain paraffins. The oxidation cannot therefore proceed through alcohols as primary intermediates, and the hydroxylation theory is thus inapplicable to these liquid-phase oxidations. It is suggested that the sequence hydrocarbon-hydroperoxide-ketone represents the major course for the reaction in the early stages of the oxidation. From the variation of the inhibited rate with time, a theoretical treatment has enabled the chain length of the uninhibited oxidation to be determined. For instance, at 120° C the chain length is 142 ± 10. The ‘activation energy’ of the chain length is — 13.3 ± 2 kcal.: thus at 20° C the chain length would have a value of 48,000. From this activation energy and that of the overall reaction, the activation energy of the chain initiation reaction has been found to be 28.2 ± 2.5 kcal. In the heavy-metal catalysed oxidation the rate is independent of the catalyst concentration above a certain value. This may be explained by the hypothesis that the heavy-metal catalyst both starts and stops reaction chains responsible for hydroperoxide formation. The phenomena of positive and negative catalysis follow, according to relative efficiency of the heavy-metal catalyst in these two reactions.

An Investigation of Adsorbed Films by Means of a Photoelectric Counter

A photoelectric tube counter of special design has been used for investigating adsorbed layers on a gold surface. The high sensitivity of the counter allows accurate measurements of photoelectric thresholds to be made with continuous ultraviolet light from a source of moderate intensity. The variation of the work function φ with the amount of adsorbed material can thus be followed quantitatively and continuously. The formation of gold oxide layers proceeds over definite steps with increases of 0.35 volt in the work function. The adsorption of iodine is reversible and the resulting increase in the work function varies with the iodine pressure according to a Langmuir isotherm, the saturation value being Δφ = +0.21 volt. The adsorption of ethyl alcohol is also reversible, but gives rise to a double threshold, suggesting the existence of liquid islands on the gold surface.

Studies in the Autoxidation of Monolayers I. The Mechanism of Autoxidation of Maleic Anhydride β‐Elaeostearin

The autoxidation of monolayers of maleic anhydride β‐elaeostearin is examined in detail and a free radical mechanism proposed. The effect of temperature and pressure on the rate of oxidation over a very wide pH range has been investigated, and the variation of oxidation rate with pH shown to be of the form to be anticipated from the postulated mechanism. The absolute values of such constants as can be separately determined are consistent with the physical picture of the process.