Showing papers in "Transactions of The Faraday Society in 1946"

Kinetic Studies in the Chemistry of Rubber and Related Materials. II. The Kinetics of Oxidation of Unconjugated Olefins

Abstract: A brief review is given of kinetic work on the oxidation of representative mono, 1,4 and 1,5 olefins. The essential process in each case is identified as a chain reaction in which hydrocarbon radicals are formed, absorb oxygen, and then react with another molecule of olefin to give a hydroperoxide and a new free radical. Three methods of chain initiation are considered: (1) direct attack of oxygen on the olefin, (2) thermal decomposition of the hydroperoxide, (3) thermal decomposition of added benzoyl peroxide. Chain termination results from interaction of two free radicals; except at low oxygen pressures, these are both peroxidic.

Peroxidation in Relation to Olefinic Structure

Abstract: The process of autoxidation among olefinic substances comprises two major phenomena, that of the incorporation of molecules of oxygen (peroxidation), and that of secondary change (peroxide breakdown) during which the peroxide groups formed by this incorporation act as oxidizing agents for adjacent unsaturated centers. Interest may, accordingly, be directed towards two quite distinct but composite themes, viz. : (1) the nature of the mechanism by which the oxygen molecules are incorporated, the positions they take up in different kinds of organic molecules, and the effect of their introduction in causing (or not causing) specific types of molecule-linking, and (2) the inherent stability or instability of the peroxide groups in different molecules and its structural cause, the mechanism of breakdown of the peroxidic groups and the way this is influenced by light, heat, or catalytic influences, and finally the manner of utilization of the “active” oxygen given up by the decomposing peroxide groups i...

Kinetic studies in the chemistry of rubber and related materials. III. Thermochemistry and mechanisms of olefin oxidation

Abstract: A new estimate of the O—O bond strength in hydroperoxides is reported, based on a determination of the heats of oxidation of ethyl linoleate and linolenate. This value is employed, together with other known bond strengths and resonance energies, to estimate the heats of a number of alternative oxidation reactions of olefins. By considering the effects of the olefin structure on these heats of reaction, it is possible to see how structural differences can lead to the formation of different oxidation products. The discussion is confined to primary products of the oxidation chain, but, even so, a considerable diversity of behavior is shown to be possible. The final material may include simple monomeric hydroperoxides, polymers with varying amounts of oxygen incorporated in the chain, cyclic peroxides, and scission products. The very limited experimental evidence available falls generally into line with expectation.

The statistical length of long-chain molecules

Abstract: A formula is derived for the complete function representing the probability of a given distance between the ends of a chain of universally jointed equal links. The formula is computed for chains of 25 and 100 links. The distribution functions derived from this formula are compared with those previously worked out by an independent method for polyisoprene and paraffin chains. It is shown that the polyisoprene chain is statistically equivalent to a randomly-jointed chain of length corresponding to 1.42 links per isoprene unit. This work forms part of a program of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.

The Interaction between Rubber and Liquids. VIII. A New Examination of the Thermodynamic Properties of the System Rubber ± Benzene

Abstract: New vapor pressure data are reported for rubber-benzene mixtures, and used to calculate thermodynamic functions for the system. The heat of dilution is comparable with that measured calorimetrically for a polyisoprene of low molecular weight. Comparing the results with the available theoretical calculations it is shown that a significant contribution to the entropy and heat of dilution of polymer solutions at low concentrations results from the occurrence of polymer-polymer contacts within individual molecules due to statistical kinking. Our thanks are due to J. L. Bolland, (Miss) J. Ferry, and H. P. Koch for the experimental assistance acknowledged in the text. The work described in this paper forms part of the program of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.