Joseph Weiss

The Rate Constant of the Reaction between Hydrogen Peroxide and Ferrous Ions

The rate constant of the reaction between hydrogen peroxide and ferrous ions has been measured in sulfuric acid solutions, by direct spectrophotometric observations of the ferric salt produced at λ=304 mμ. It has been confirmed that the rate is independent of acidity (measurements were carried out from 0.05 N to 0.8 N H2SO4) and that the reaction is bimolecular within a wide range of the concentrations of the reactants; the hydrogen peroxide concentration was varied in the ratio 1:25 and the ferrous sulfate in the ratio 1:20. The rate constant, which has been measured within the temperature range of 15° to 40°C, can be represented by the equation k1=1.05×108×exp(−8460/RT)1 moles−1sec−1.

The autoxidation of ferrous ions in aqueous solution

Der Primärprozess des bereits vor einiger Zeit gegebenen Mechanismus der Autoxydation von Ferroionen in verdünnten wässrigen Lösungen wurde erneut diskutiert, besonders im Hinblick auf die Rolle von elektrostatischen Wechselwirkungen bei der Bildung des primären Ionenkomplexes. Es zeigt sich, dass Coulombsche Wechselwirkungen, auch mit anderen in der Lösung vorhandenen Ionen, von Bedeutung für die Stabilisierung des primären Ionenkomplexes sein können, und es ist sehr wahrscheinlich, dass, ganz allgemein, solche Wechselwirkungen bei Elektronenübergangsprozessen in Lösungen in Betracht gezogen werden müssen.

The Free Radical Mechanism in the Reactions of Hydrogen peroxide

Publisher Summary This chapter describes and illustrates the reaction between hydrogen peroxide and ferrous ions, hydrogen peroxide and ferric ions, hydrogen peroxide and cupric ions, hydrogen peroxide at different metal surfaces, the photochemical decomposition of hydrogen peroxide, the decomposition of hydrogen peroxide by ionizing radiations, the reaction between ozone and hydrogen peroxide and the decomposition of ozone in aqueous solution, detection of free OH radicals, and some thermodynamics data concerning the radicals OH and HO 2 . Hydrogen peroxide decomposes under the influence of ionizing radiations (x-rays, and γ-rays), but hardly any quantitative data are available currently, except for the decomposition by X-rays in dilute aqueous solutions. A quantitative treatment of the decomposition of hydrogen-peroxide by ionizing radiations is still lacking. A preliminary investigation presents a number of interesting features.

THE ACTION OF X-RAYS ON FERROUS AND FERRIC SALTS IN AQUEOUS SOLUTIONS

The action of X-rays on the ferrous-ferric system has been studied under a variety of conditions. The H atoms and OH radicals formed primarily by the action of the radiation on the water react according to Fe3+ + H → Fe2+ + H+ and Fe2+ + OH → Fe3+ + OH-. Experiments carried out in the presence of molecular hydrogen, where the latter reaction competes with the reaction H2 + OH → H2O + H, permit us to deduce that the specific rate constant of the reaction between OH radicals and ferrous ions is about five times greater than that of the corresponding reaction with hydrogen molecules. The study of the pH dependence of the reaction has led to the assumption that molecular hydrogen ions, H+2(hydr.), intervene in this process undergoing the reaction Fe2+ + H+2(hydr.) → Fe3+ + H2, and that these ions exist in the equilibrium: H + H+(hydr.) ⇌ H+2(hydr.). Experimental evidence and some theoretical considerations which have led to the assumption of H+2 in aqueous systems have been discussed in detail. In the presence of molecular oxygen the hydrogen atoms react according to H + O2 → HO2, followed by reactions of the latter radical (cf. Haber & Weiss 1934). A comparison of the experimentally determined yields under different conditions with the absolute (chemical) yields as derived from the proposed mechanism has led to the estimation of the energy (WH2O) required for the production of a radical pair (H + OH) by the action of X-rays on water. This has been found to be WH2O = 19⋅4 ± 0⋅4 eV.

Studies on the action of x-rays on aqueous solutions of nucleic acids and some nucleotides.

Die Wirkung von Röntgenstrahlen (200 kV) auf wässerige Lösungen von Nukleinsäuren und Nukleotiden wurde unter besonderer Berücksichtigung des Einflusses von molekularem Sauerstoff und Wasserstoffsuperoxyd untersucht. Der so gefundene, nach der Bestrahlung einsetzende Abfall der Viskosität von D.N.A.-Lösungen (after-effect) kann als Hydrolyse der durch die Bestrahlung labilisierten Kohlenstoff-Phosphat-Bindungen angesehen werden. Untersuchungen über die Hydrolyse von bestrahlten Nukleotiden, -P.N.A.- und D.N.A.-Lösungen stehen in vollem Einklang mit obiger Annahme.

Photochemistry of Ferrous Ions in Aqueous Solution

The photochemistry of ferrous ions in aqueous solutions has been investigated, and it has been confirmed that irradiation in the quartz ultraviolet, in the absence of oxygen, leads to the formation of ferric salt and molecular hydrogen. It has been concluded further that the primary absorption of a light quantum results in the formation of excited ions, (Fe2+·H2O)*, a considerable proportion of which undergo processes of deactivation, while the remaining (about one‐tenth) dissociate according to (Fe2+·H2O)*→Fe3++OH−+H, leading to the formation of hydrogen atoms. The latter can undergo back reactions of the type Fe3++H→Fe2++H+. Investigation of the pH dependence of the quantum yield has led to the assumption that hydrogen atoms can also react according to H+H(hydr)+⇌H2(hydr)+, leading to the formation of hydrated hydrogen molecular ions which intervene in this process according to the reaction Fe2++H2+→Fe3++H2.Other experimental evidence and some theoretical considerations which have led to the assumption ...

The Action of X-Rays (200 kV) and

The radiation-induced decomposition of water by X -rays (200 kV) an γ-rays (60Co) has been investigated by studying the reduction of ceric salts in dilute aqueous solutions under the influence of these radiations. For the elucidation of the mechanism, the ceric reduction yields have been studied under various conditions, i. e. at different acid concentrations, in de-aerated and in oxygenated (1 atm) solutions, in the presence of dissolved hydrogen and with formic acid as an added solute. The initial reduction yields were found to be greater than the steady-state reduction yields, the following values were obtained (G in molecules/100 eV): for X-rays G(CeIII) = 3·15 ± 0·10, for γ-rays G(CeIII) = 2·45 ± 0·08. These yields were the same both in the presence and in the absence of oxygen during irradiation. In the presence of formic acid the reduction yields are increased: for X-rays G(CeIII) = 8·50 ± 0·10, for γ-rays G(CeIII) = 8·15 ± 0·10. These yields were found to be independent of the formic acid concentration in the range 0·001 to 0·05M. The yield of the gaseous products (hydrogen and oxygen) from dilute ceric salt solutions, irradiated in vacuo, were found to be: for X-rays G(H2) = 0·57 ± 0·03, G(O2) = 1·07 ± 0·05, for γ-rays G(H2) = 0·40 ± 0·02, G(O2) = 0·84 ± 0·04. A mechanism is proposed on the basis of which the experimental results can be accounted for. It has been possible to draw some definite conclusions about the primary chemical processes in the radiation-induced decomposition of liquid water; a small but significant difference in the yields of the primary chemical products for X-rays and for γ-rays has been clearly established.

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Abstract It is known that the formation of colour centres in irradiated ice is due to trapped electrons. The hypothesis is put forward that the electrons are trapped in vacancies created by the radiation-induced decomposition of water molecules in the hydrogen-bonded ice structure and displacement of the molecular fragments by (focused) collisions in the lattice. If an electron occupies such a vacancy, rotation of (two) adjacent water molecules or diffusion of Bjerrum defects induced by the field of the electron should give an efficient trap. It can also be shown that the formation of such a cavity for trapping the electron appears to be essential on energetic grounds. It is suggested that basically a similar trapping mechanism is operative in other hydrogen bonded solids and liquids.

-rays (

Nach der Bestrahlung verdünnter Lösungen von Cholesterin beziehungsweise Δ5-Pregnen-ol-(3β)-on-(20) mit Röntgenstrahlen, isolierten wir Cholestan-triol-(3β, 5α, 6β) und Δ5-Cholesten-ol-(3β)-on-(7) beziehungsweise allo-Pregnan-triol-(3β, 5, 6β)-on-(20).

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The transfer of electronic excitation energy between molecules and atoms has attracted a good deal of attention during recent years. In the case of gases, this subject has been studied mainly by physicists, and important contributions have been made by J. Franck and his school in particular. In condensed systems, the transfer of excitation energy (absorbed primarily from an external light source) and the behaviour of excited molecules form the basis for all types of photosensitized reactions. These reactions are of considerable importance for the various types of biological photosynthesis and for many technical problems.