A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.     

Two-path reduction of molecular nitrogen by transition metal hydroxides

The kinetics of the reduction of N₂ to N₂H₄ and NH₃ by Ti^III-Mo^III hydroxide was studied at pH I I and 303-333 K, and the activation energies for these reactions and also for the reaction N₂H₄ 2 NH₃ were determined (29, 70, and 25 kJ mol^– respectively). It was concluded that -90 % of ammonia was formed by the direct reduction of N₂ without intermediate formation of hydrazine. A mechanism of this reaction is suggested, which includes the proton insertion into the N-N bond favored by an enhanced electron density at the nitrogen atoms, according to the data of the quantum-mechanical calculation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1402–1405, June, 1996.     

Electrooxidation of hydrazine catalyzed by 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy (TEMPOL)

The electrocatalytic oxidation of hydrazine (N₂H₄) by TEMPOL on a glassy carbon electrode has been studied. The kinetic parameters of the electrode reaction were measured and the electrocatalytic reaction mechanism for the electrooxidation of hydrazine in the presence of TEMPOL was proposed. TEMPOL undergoes a reversible single electron transfer process at a glassy carbon electrode (GCE) at pH 1.2–8.0, and the electrochemical oxidation of N₂H₄ at a GCE can be catalyzed by TEMPOL. The catalytic current is affected by the concentration of catalyst and pH. The overall number of electrons involved in the catalytic oxidation of N₂H₄ and the number of electrons involved in the rate determining step (rds) are 4 and 1, respectively. The catalytic oxidation obeys the first-order kinetics with respect to N₂H₄. The proposed mechanism is consistent with the experimental data, and a cation intermediate [> N---O---N₂H₄⁺], formed by reaction of oxoammonium salt with N₂H₄, is involved in the reaction.     

Study of the equilibrium of formation of arsenic(iii) lacunar heteropolytungstates by Raman spectroscopy

The formation of lacunar heteropolyanions (HPA): [AsW₉O₃₃]^9–, [As₂W₁₉O₆₇(H₂O)]^14–, and [As₂W₂₀O₆₈(H₂O)]^10– in aqueous solutions was investigated by Raman spectroscopy at [Na₂HAsO₃]₀ = 0.1, [Na₂WO₄]₀ = 0.9 mol L^–1 and pH 9.4–1.6. The [AsW₉O₃₃]^9– HPA is characterized by the most intense band ns (W=O) at 948 cm^–1 retaining its position in the pH range from 8.9 to 7.5. Under these conditions, the equilibrium constant of [AsW₉O₃₃]^9– formation from H₂AsO₃ ^– and WO₄ ^2– ions was estimated (logK = 87.0±1.0). The asymmetrical band at 952 cm^–1 corresponding to H_x[As₂W₁₉O₆₇(H₂O)]^(14–x)– shifts to 960 cm^–1 as the pH decreases from 6.5 to 5.5, which is due to the change in HPA protonation. The [As₂W₂₀O₆₈(H₂O)]^10– HPA is formed at pH 3.1—1.6; it is characterized by a band at 972 cm^–1.     

Pulse radiolysis studies on the reactions of 3-pyridinol with oxidizing radicals

Reaction rate constants for the reactions of 3-pyridinol with oxidizing radicals viz. OH, N₃, Br ₂ ^– , Cl ₂ ^– , SO ₄ ^– and O^– have been determined in aqueous solutions at different, pH's. Absorption spectra of the product transient species have been recorded in the 320–600 nm region. In the alkaline region (pH 13) the N₃ reaction product decays in two steps and O^– does not bring about one-electron oxidation. Similarly, at neutral pH, SO ₄ ^– does not cause selective one-electron oxidation of 3-pyridinol.     

The kinetics of the reaction of iodine with hydrazine as studied by pulse radiolysis

Pulse radiolysis was utilized to study the iodine — hydrazine reaction in aqueous solutions of pH3 to 7, at I^– concentrations of 0.02 to 0.34M, and a constant ionic strength of 0.35M. The reaction rate was found to be proportional to [H⁺]^–1 and [I^–]^–1. Experimental results support the assumption that the rate-determining step is the reaction of I₂ with N₂H₄ with a rate constant K1.2×10⁷ M^–1s^–1.     

The low temperature synthesis of metal oxides by novel hydrazine method

The hydroxide, oxalate and citrate precursors of the metal oxides such as γ-Fe₂O₃, (MnZn)Fe₂O₄, Cu(K)Fe₂O₄, BaTiO₃, La(Sr)MnO₃, La(Sr)AlO₃, La/Gd(Ca/Ba/Sr)CoO₃, and anatase TiO₂ on modifications with the hydrazine decompose at low temperatures give single phase oxides of superior properties, while the complexes without such modification require higher temperatures for achieving the phases. The hydrazine released at lower temperatures reacts with the oxygen in the atmosphere, N₂H₄+O₂→N₂+2H₂O; ΔH=−625 kJ mol⁻¹, and liberates enormous energy that is sufficient for the oxidative decomposition of the complexes now devoid of hydrazine. Such extra energy is not available in the case of the precursors without such modifications. The reaction products of hydrazine oxidation provide desired partial pressure of moisture needed for the stabilization of γ-Fe₂O₃. Also, the nitrogen that is formed in the reaction of hydrazine with oxygen gets trapped in the lattice of TiO₂ giving yellow color nitrogen doped TiO_2−xN_x photocatalyst. Thus, hydrazine method of preparation has many advantages in the preparation of metal oxides of superior properties.     

Effect of heating on dissociation of water vapor in high-frequency plasmas and formation of hydrogen peroxide in a cold trap downstream of the plasma

At low flow rates (0.7–2.8 mmol hr^–1) and long residence times (2.3–8.5 s) nearly 60% of the input water vapor was decomposed by a 13.56-MHz rf discharge. Downstream of the discharge a trap cooled by liquid nitrogen collected nearly constant yields of H₂O₂. The decomposition is representable by the equation 2H₂O=H₂O₂+H₂. The overall rate of decomposition was found to depend on the absorbed power density. Heating the rf plasma and its spatial afterglow from 25 to 600°C did not significantly change the percent decomposition of H₂O and the formation of H₂O₂. Above 600°C, however, a continuous decrease in H₂O₂ yield was observed with increasing temperature, and this was associated with the increasing formation of H₂O from the dissociated products such as highly excited OH radicals which otherwise produce the precursors of H₂O₂. The same heating effects were observed in the case of the spatial afterglow of a 2.45-GHz microwave cavity discharge in water vapor under essentially similar conditions. It appears that at the high temperatures the reaction OH+OHH₂O+O is favored over the reaction O+OHO₂+H. This limits the formation of O₂ and consequently decreases the H₂O₂ yield.     

Ferrous ion oxidations by √H, √OH and H2O2 in aerated FBX dosimetry system

In the ferrous ion, benzoic acid and xylenol orange (FBX) dosimetric system, benzoic acid (BA) increases the G(Fe³⁺) value. Xylenol orange (XO) controls the BA sensitized chain reaction as well as forms a complex with Fe³⁺. In the aerated FBX system each √H, √OH and H₂O₂ oxidizes 8.5, 6.6 and 7.6 Fe²⁺ ions, respectively; and these values respectively increase to 11.3, 7.6 and 8.6 in oxygenated solution. About 8% √OH reacts with XO and the remaining with BA. The above fractional values are due to this competition. This √OH reaction with XO oxidizes 1.8% and 2.1% ferrous ions only in aerated and oxygenated solutions, respectively. There is a competition between √H reactions with O₂ and with BA, but both lead to the production of H₂O₂. The oxidation of Fe²⁺ by √OH reactions at different concentrations of H₂O₂ is linear with absorbed dose while the √H reactions make the oxidation of Fe²⁺ non-linear with dose. This is due to competition reaction of H-adduct of BA between O₂ and Fe³⁺.     

Acid Catalysis in Reaction of Ozone with Chloride Ions

The kinetics of the interaction of ozone with aqueous solutions of chlorides resulting in Cl₂ evolution to the gas phase was studied. The reaction of O₃ with Cl^– is accelerated by H⁺ ions. The effects of the concentrations of H⁺ and Cl^–, the ionic strength, and temperature (ranged from 7 to 60°C) on the reaction rate were studied. A mechanism explaining the experimental kinetics was proposed. The acid catalysis is due to the formation of the HO₃Cl complex, which is in equilibrium with H⁺, O₃, and Cl^–. The constants of reactions involved in the proposed mechanism were determined.     

Copper(II)–1,2-bis(thiocarbamoyl)hydrazine and copper(II)–(1-carbamoyl-2-thiocarbamoyl)hydrazine complexing in copper(II)hexacyanoferrate(II) gelatin-immobilized matrix systems

The complex formation that occurs in gelatin-immobilized copper(II)hexacyanoferrate(II) matrices upon contact with aqueous alkaline (pH 12.0) solutions of 1,2-bis(thiocarbamoyl)hydrazine, H₂NC(S)NHNHC(S)NH₂ and 1-carbamoyl-2-(thiocarbamoyl)hydrazine, H₂NC(O)NHNHC(S)NH₂ has been studied. The reaction of each of these ligands with copper(II) is preceded by the destruction of copper(II)hexacyanoferrate(II) in an alkaline medium to form a polymeric copper(II) hydroxide, which is involved in the subsequent copper(II)–ligand complex formation. In both Cu^II–N ligand systems, two complex compounds are formed; the water-insoluble Cu₂B₂(H₂O)₂ dimer and a water-soluble product of tentative composition [CuB(HB)]^– (H₂B=ligand).     

A phosphate catalyzed reaction of iodine with hydrazine in aqueous solutions

Pulse radiolysis was utilized to study the kinetics of the iodine-hydrazine reaction in aqueous solutions containing phosphate buffer in the pH range 5.5 to 7. The reaction rate was found to be proportional to and [I^–]^–1, but did not show simple proportionality to [H⁺]^–1 and was considerably higher than that found earlier when the pH of solutions was adjusted with HClO₄ or H₃BO₃. The results are in a formal agreement with the assumption that in phosphate buffered solutions a complex N₂H₄. HPO ₄ ^2– is formed, reacting with I₂ with a rate constant which is greater than that ascribed earlier to the reaction of N₂H₄ with I₂/Ref. 1/.     

Quantum yields of [W(CN)8]4− formation in charge-transfer photochemistry of octacyanotungstate (V)

Summary The reactions of monochromatically photolyzed aqueous [W(CN)₈]^3– solutions in the pH range 1–13 were found to consist of a two-step sequence involving a primary inter-molecular redox process and a consecutive thermal chain process, both leading to the formation of octacyanotungstate(IV) as the main reaction product. The initial quantum yields, ₀, are practically constant for the entire pH range and equal to 0.81±0.05 mole/Einstein. The final quantum yields, _f, for both neutral and alkaline solution, were found to be greater than 1, having also an approximately constant value of 3.42±0.25. The empirical rate law for the post-irradiation reaction under excess of [W(CN)₈]^3– and at constant pH is given by: rate = k_obs[R]²[W(CN) ₈ ^4– ]^–2 where R is a one-electron reductant. Kinetic data suggest a mechanism of the Haber-Weiss type for the thermal reduction of [W(CN)₈]^3– by H₂O₂.     

Elektrometrische Untersuchungen von Uranylarseniten

Zusammenfassung Mit Hilfe der pH- und konduktometrischen Titrationen wurde die Stöchiometrie der Verbindungen untersucht, die bei der Reaktion von Uranylnitrat mit Alkali-Ortho-, Pyro- und Metaarseniten entstehen. Der Verlauf der Titrationskurven zeigt klar die Bildung der Verbindungen 3 UO₂O · As₂O₃, 2 UO₂O · As₂O₃ und UO₂O · As₂O₃ in den pH-Bereichen 7,0–9,9 bzw. 6,0–7,5 bzw. 5,0–6,8. Der Anteil von Uranyl in den Alkaliarseniten wächst mit wachsender Konzentration von Na₂O. Die Bildung der Uranylarsenite ist also eine Funktion der H⁺-Ionenkonzentration. Wir fanden, daß die Ausfällung dieser Verbindungen fast quantitativ ist.

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The stoichiometry of the compounds formed by the interaction of uranyl nitrate and different alkali arsenites (ortho-, pyro-, and meta-) have been investigated by means of pH and conductometric titrations. The breaks and inflections in titration curves provide cogent evidence for the formation of 3 UO₂O · As₂O₃, 2 UO₂O · As₂O₃ and UO₂O · As₂O₃ in pH ranges 7.0–9.9, 6.0–7.5 and 5.0–6.8 respectively. The proportion of uranyl increases with the increase in the concentration of Na₂O molecules in alkali arsenites. The formation of uranyl arsenites is thus a function of H⁺ ion concentration. The precipitation of these compounds has been found to be almost quantitative.

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Mit 4 Abbildungen     

Mechanism of OH radical-induced oxidation of <Emphasis Type="Italic">p</Emphasis>-cresol to <Emphasis Type="Italic">p</Emphasis>-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H₃O⁺ concentration yielding a bimolecular rate coefficient of 1.8 × 10⁸ mol^–1 dm³ s^–1. In the alkaline range a linear dependence was found on the OH^– concentration with rate coefficient of 4.9 × 10¹⁰ mol^–1 dm³ s^–1. These findings were interpreted in terms of acid-base catalysis of the H₂O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH₃C₆H₄OH^+. was not observed as intermediate.     

Compounds of WVI with 1(+)-sorbitol: Study of formation and interconversion equilibria

Summary The polarimetric study of the W^VI-sorbitol system shows the formation of three stable complexes. The species stable at higher pH is monomeric ([WO(OH)(C₆H₁₂O₆)₂]^–), while the other two are dinuclear complexes of different stoichiometries ([W₂O₃(OH)₄(C₆H₁₀O₆)]^–2 and [W₃O₃(OH)(C₆H₁₁O₆)₂]^–). The interconversion equilibria have been established and the formation constants determined. The behaviour of sorbitol is like that displayed by other polyhydroxylic ligands having one or two carboxylic groups. The substitution of a carboxylic group for an alcoholic one seems only to result in lower stability constants for the complexes formed.     

Catalytic effect of iron wires on the syntheses of ammonia and hydrazine in a radio-frequency discharge

The catalytic effect of iron wires on plasma syntheses of ammonia and hydrazine has been studied in the nitrogen-hydrogen plasma prepared using rf discharge at a pressure of 650 Pa (5 Torr). The product was mainly ammonia including a small amount of hydrazine. When iron wires were placed in the plasma downstream of the gas flow, the yields of both products increased, about two times in ammonia and two orders of magnitude in hydrazine. The yields increased with increasing number of wires (the surface area of the catalyst). The dissociative adsorption of nitrogen molecules and/or molecular ions on the iron surface and the formation of NH_x by the reaction with hydrogen in the plasma followed by the formation of NH₃ or N₂H₄ are considered as a reaction scheme. This is supported by the identification of NH₃ with XPS of the surface of iron wires.Partly presented at the 10th International Symposium on Plasma Chemistry, August 4–9, 1991, Bochum, Germany.     

An open-shell INDO study of models for the stabilized O− ion in γ-irradiated alkaline ices

Structural models for stabilized O^– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O^– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH^– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O^– models. The hydrated O^– model is closely similar to the hydrated anions in KF · 4H₂O, NaOH · 4H₂O, and NaOH · 7H₂O. A second model is developed, involving H₃O⁺ along with H₂O, in the O^– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry.     

Hydroxoaquotetraminecobalt(III)-promoted hydrolysis of pyrophosphate. Mechanistic considerations

The hydrolysis of pyrophosphate was investigated at two different concentrations (10^–2 and 10^–3M) of [N₄Co(H₂O)(OH)]²⁺ [N₄=tn₂ or trpn (tn=trimethylenediamine, trpn=tris(3-aminopropyl)amine)] using two quenching methods (Eu^II/H⁺ and OH^–). The reaction was monitored by measurement of orthophosphate (Pi) in quenched aliquots of a reaction mixture consisting of the reagents added to a reaction mixture consisting of the reagents added to a preformed 1:1 pyrophosphate complex (tn₂CoPPi). The results are compared with similar findings in the literature for cyanide-quenched reaction mixtures. The reactive species with regard to hydrolysis was found to be a 3:1 N₄Co^III to PPi complex. Factors affecting the formation and degradation of this reactive species are discussed.     

Sulfito- und Thiosulfato-Komplexe des Kobalts(III) mitα-Benzildioxim Überα-Dioximinkomplexe der Übergangsmetalle, 52. Mitt.

Some new ligand exchange reactions of [Co(diph·H)₂Cl(H₂O)] and [Co(diph·H)₂(SO₃)(H₂O)]^– complexes with N₃ ^–, S₂O₃ ^2– and with aromatic and heterocyclic amines were carried out. A series of derivatives of the types [Co(diph·H)₂(SO₃)X] ^n– (X=N₃ ^–, S₂O₃ ^2– oramine) and [Co(diph·H)₂(S₂O₃)₂]^3– were described and characterized. Some structural problems are resolved and discussed on the basis of UV and IR spectral data.