Studies on the decomposition and photo-formation of hydrogen peroxide

THE THERMAL DECOMPOSITION OF H₂0₂ VAPOUR1. A convenient method for the preparation of small quantities of chemically pure, very concentrated hydrogen peroxide has been further developed.2. The decomposition of hydrogen peroxide vapour has been examined on various surfaces at pressures up to 5 mms. at various temperatures in the range 18 - 110 °C. The appearance of both second and first order characteristics on a silica surface is attributed to a change in the surface action rather than to a strong retardation of the decomposition by water vapour.3. Octa -decyl alcohol was found to give a very stable surface and very reproducible results were obtained in a silica vessel coated with this compound Oxygen, nitroen, water vapour and carbon dioxide were found to have no effect on the rate of decomposition.4. Films of cobalt salts were found to accelerate the rate of decomposition but acetanilide and octadecyl alcohol gave rates which were of the same order of magnitude as on the uncoated silica surface.5. The second order decomposition was found to have a negligible temperature coefficient but the first order decomposition had a heat of activation of approximately/ approximately 12 k.cals. per mole, both on a silica surface and octa- d.ecyi alcohol.6. - With high pressures of water vapour, periodic variations in pressure were observed. A possible explanation of this behaviour is discussed.7. Since high pressures of oxygen and nitrogen (400 mms.) have no effect on the rate, it is suggeste that the rate of diffusion in the bulk of the vapour has no effect on the rate of decomposition.8. An attempt has been made to evaluate the absolute velocity of reaction from an equation derived from the theory of absolute reaction rates. The velocity so determined was found to be 4.4 x 10¹² molecules H₂0₂ cm⁻² sec⁻¹ at a temperature of 27.2 °C on an octa -decy alcohol surface, in good agreement with the experimental value of 6.9 x 10⁻¹² molecules H₂0₂ cm.⁻² sec.⁻¹THE PHOTO -FORMATION OF H₂0₂1. Zinc oxide, titanium dioxide and zinc sulphiac nave been shown to adsorb dry oxygen on illumination with visible light. This adsorption is. partially reversible.2. Aqueous suspensions of zinc oxide, titanium dioxide and zinc sulphide produce an oxidising agent when illuminated in presence of oxygen.3. The oxidising agent produced, in the case of inc oxide suspensions, has been shown to be hydrogen eroxide.4. Several mechanisms suggested to explain the degrading action of photosensitive dyes on textiles are discussed and their application to the activity of the white pigments considered.5. An activated form of oxygen, either an excited molecule or an oxygen ion, is suggested as being formed. .n the illumination of the white pigments in dry oxygen. This activated oxygen is considered to be an intermediate in the formation of hydrogen peroxide in aqueous suspensions