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Time-resolved pulse radiolysis studies have been carried out on the R2S+· R2S ⇆ (R2S.˙.SR2)+ equilibrium and associated decay kinetics of sulfur centered radical cations. - Equilibrium constants of K = 2.0 · 105 and 5.4 · 102 mol−1 dm3 at 20°C have been determined for the species with R = CH3 and (CH3)2CH, respectively. Absolute rate constants have been measured for the back reaction of the above equilibrium: k-1 = 1.5 · 104 s−1 and 5.6 · 106 s−1, respectively, at 20°C. Further rate constants refer to the deprotonation of R2S+ by various proton acceptors (phosphate, acetate and water). - ΔH≠ = 57 kJ mol−1 and 17 kJ mol−1 were determined for the dissociation of the sulfur-sulfur 3-electron bond in (Me2S.˙.SMe2)± and (i-Pr2S.˙.S i-Pr2)+, respectively. On this basis the S.˙.S bond energies were estimated to ≲80 kJ mol−1 and ≲40 kJ mol−1 for these two species. The kinetic and thermodynamic results substantiate previous conclusions on the electronic structure and relative stability of S.˙.S bonded radicals and corroborate some theoretical calculations.

Polyethylene terephthalate (PETP) forms the basis of a new plastics material, Hostadur®, which is suitable for mouldings in engineering applications which are subject to mechanical stress. The crystallisation behaviour of PETP is discussed as this is an important factor if economic processing by injection moulding is to be obtained. Short-term properties of the material such as stiffness, strength and toughness were found to be good. Creep rupture strength, and fatigue strength under alternating stress, as well as other long-term properties, were found to be better than with other thermoplastics such as polyamides and polyacetals.

Tetranitromethan (TNM) reagiert mit freien H-Atomen und hydratisierten Elektronen aus der γ-Radiolyse des Wassers, wobei je Atom bzw. Elektron eine Molekel Nitroform entsteht. Die Nitroformausbeute, die gleich ist der Summe G (H) + G (e), nimmt mit steigender Konzentration des TNM langsam zu, was auf das Eingreifen des TNM in nmolekulare“ Prozesse innerhalb der Ionisations- und Anregungsgruppen zuruck-gefuhrt wird. In Gegenwart von N2O wird eine geringere Nitroformausbeute beobachtet. Die quantitative Untersuchung dieser Abnahme fuhrte zu folgenden Ausbeuten und Geschwindigkeitskonstanten: G(Hα) = 0,6, G (e) = 2,7,k = 6,2 · 1010 Mol−1 liter sec−1. In Gegenwart von 0,2 Mol/l Isopropanol betragt die Nitroformausbeute 6,3. Daraus wird abgeleitet, das in der γ-Radiolyse des Wassers OH-Radikale mit einer Ausbeute von 3,0/100 eV erzeugt werden. (Alle Ausbeuten gelten fur eine 6,4 · 10−4 molare TNM Losung.) Tetranitromethane (TNM) was found to react with free H-atoms and hydrated electrons produced in the γ-radiolysis of water. One molecule of trinitromethane is formed per atom or electron, respectively. The yield of trinitromethane, which is equal to the sum of G (H) and G (e), slowly increases with TNM-concentration. This is explained by the influence of TNM on “molecular” processes in the spurs. In the precence of N2O, lower yields of trinitromethane were observed. The quantitative investigation of this decrease led to the following yields and rate constant: G (Hα) = 0,6 G (e) = 2,7,k = 6,2 · 1010 mole−1 liter sec−1. The yield of trinitromethane amounts to 6.3 when isopropanol is present at 0.2 moles/liter. It follows from this observation that OH-radicals are formed with a yield of 3.0/100 eV in the γ-radiolysis of water. (All yields refer to a 6.4 · 10−4 molar TNM-solution.)

Die absoluten bimolekularen Geschwindigkeitskonstanten der Reaktionen des Tetranitromethans mit hydratisierten Elektronen, Wasserstoffatomen, verschiedenen Alkoholradikalen und mit den Ionen O2−, CH3COCH3− und Cu+ wurden bestimmt. Ferner wird ein Verfahren beschrieben, um Tetranitromethan als „Indikator” fur freie Radikale, die keine starke Lichtabsorption besitzen, zu verwenden. Auf diese Weise wurde die Reaktion OH + CH3OH H2O + CH2OH untersucht. Alle Reaktionen des Tetranitromethans sind sehr schnell und werden im wesentlichen durch die Diffusion der Reaktanden kontrolliert. Die Bildung des aci-Nitroforms bei diesen Reaktionen wird auf die Ubertragung eines Elektrons von dem Reaktionspartner auf das Tetranitromethan mit sofortiger Dissoziation des negativen Molekelions zuruckgefuhrt. Freie neutrale Radikale ubertragen etwa gleich schnell wie negative Radikalionen, wahrend die Ubertragung vom Cu+-Ion langsamer geschieht. Fur die Reaktion des OH-Radikals mit Methanol wurde eine uberraschend hohe Geschwindigkeitskonstante von mehr als 3 · 109 Mol−1 1 sec−1 gefunden; auch dieser Prozes scheint demnach weitgehend durch die Diffusion der Reaktionspartner bestimmt zu sein. The absolute rate constants of the reactions between tetranitromethane and hydrated electrons, hydrogen atoms, various alcohol radicals and the ions O2−, CH3COCH3− and Cu+ have been determined. A procedure is also described to use tetranitromethane as „indicator” for free radicals which have no strong light absorption. The reaction OH + CH3OH H2O + CH2OH has been investigated this way. All reactions of tetranitremethane are very fast and essentially are controlled by the diffusion of the reactands. The formation of aci-nitroform in these reactions is explained by electron transfer from the reaction partner to tetranitromethane and immediate dissociation of the negative molecule ion. Neutral free radicals transfer the electron about as fast as negative radical ions while a slower transfer occurs from the Cu+-ion. A surprisingly high rate constant of more than 3 · 109 mole−1. 1 sec−1 has been found for the reaction of the OH radical with methanol. It therefore seems that this process is also determined by the diffusion of the reactands.

A significant property of an oxidized sulfur atom is its high tendency to coordinate with a free electron pair from a second sulfur atom. This leads to the establishment of three-electron bonds between the two sulfurs as formulated for organic sulfides. The electronic structure of the three-electron bond is characterized by two bonding sigma-electrons and one antibonding, i.e. bond weakening sigma/sup */-electron. Identification of most of these three-electron bonded systems has been made by e.s.r. and by optical spectroscopy in aqueous environment. A particularly useful tool has been proven to be the radiation chemical technique of pulse radiolysis which allows a time-resolved observation of short-lived species. Current questions of interest are the stability of these three-electron bonds and possible unique chemical characteristics of this and other types of sulfur-centered radicals. Both subjects are discussed, with particular emphasis on recent advances in the oxidation of organic sulfides. The examples discussed refer mostly to radiation chemical studies with aqueous solutions. In such experiments oxidations can conveniently be initiated by hydroxyl radicals formed upon irradiation of the water, or by secondary radicals derived therefrom.

Bei H2S-Konzentrationen von etwa 10" M last sich in wasriger Losung von niedrigem pH-Wert (0.2 M HClO4) pulsradiolytisch gemas Reaktionen A-Bdas bei 370 nm absorbierende Radikalkation [H2SSH2]Terzeugen.

Es wurden pulsradiolytische und γ-strahlenchemische Versuche zur Reduktion von halogenierten organischen Verbindungen durch hydratisierte Elektronen durchgefuhrt. Dissoziativer Elektroneneinfang setzt aus verschieden chlorierten Methanen, athylenen sowie fluorierten Benzolen Halogenionen frei. Diese wurden mit Hilfe von Leitfahigkeitsmessungen bei der Pulsradiolyse und mit Ionen-sensitiven Elektroden bei den γ-Versuchen quantitativ nachgewiesen. Die Geschwindigkeitskonstanten der Reaktion des eaq− mit den mehrfach halogenierten Verbindungen sind praktisch ausschlieslich durch die Diffusion der Reaktionspartner zueinander bestimmt. Bei den wenig halogenierten Substanzen verlauft die Reaktion langsamer, was mit der groseren Stabilitat der Halogen-Kohlenstoffbindung in Einklang steht. Die primaren Reaktionsprodukte sind Halogenionen und neutrale, kurzlebige Radikale, die keinerlei optische Absorption im Wellenlangenbereich von 250–800 nm aufweisen. Alkohol- und Atherradikale ubertragen ein Elektron auf CCl4. Dies stimmt mit der Tatsache uberein, das die Halbstufenpotentiale fur die Oxidation dieser Radikale negativer sind als dasjenige fur die Reduktion des CCl4. Die theoretisch ebenfalls mogliche Elektronenubertragung vom CO2−-Radikalion auf Tetrachlorkohlenstoff findet nicht statt, da offensichtlich eine zu hohe Aktivierungsenergie fur diese Reaktion vorliegt. The reduction of halogenated organic compounds by hydrated electrons has been investigated by means of pulse radiolysis and γ-irradiation. Halide ions are produced in a dissociative electron capture process by chlorinated methanes and ethylenes, and fluorinated benzenes. A quantitative analysis of the halide ion yield has been carried out by conductivity pulse radiolysis methods, and with ion specific electrodes. The rate constants of the reaction of hydrated electrons with the highly halogenated compounds were found to be essentially diffusion controlled. The slower reaction of eaq− with the less halogenated compounds is explained by the higher stability of the carbon-halogen bond in these molecules. The primary products of the dissociative electron capture process are halide ions and neutral radicals which have no optical absorption in the 250–800 nm range. Carbon tetrachloride is also reduced by an electron transfer reaction from alcohol and ether radicals. This agrees with the fact that the halfwave oxidation potential of these radicals is more negative than the halfwave reduction potential of CCl4. A theoretically possible electron transfer process from CO2− ions to CCl4 has not been observed, presumably due to a high activation energy of this reaction.