Kinetics and spectral properties of electron and •OH adducts of dimethylpyridines: a pulse radiolysis study

The reactions of e_aq ^-, OH, O^- and SO^- ₄ with 2,4-, 2,6- and 3,5-dimethylpyridines have been investigated in aqueous solution by pulse radiolysis with optical detection. Both e_aq ^- and OH radicals have high reactivity toward these compounds with k = (4-8) × 10⁹ dm³ mol^-1 s^-1. The rates of O^- and SO₄ ^- reactions ((1-3) × 10⁹ dm³ mol^-1 s^-1) were lower compared to the rate observed with the OH radical. The transient absorption spectra obtained in the reaction of e_aq ^- with three isomers exhibited a weak broad band around 340-410 nm. The absorption maxima of the intermediates formed in the OH and SO₄ ^- reactions were centred around 320-330 nm ( = 2450-3500 dm³ mol^-1 cm^-1) with an additional broad peak in the range 460-520 nm which are attributed to the corresponding OH adducts. The spectra in the O^- reaction have absorption maxima between 300 and 320 nm and it reacts both by addition and H-abstraction from the CH₃ group. A reaction mechanism consistent with the observed results is proposed.     

Radical scavenging properties of a flavouring agent–Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin (V-OH) with azide radicals, at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 × 10⁷ and 2.5 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O) formed either at pH 6 or 9, showed a _max at 410 nm. At pH 5, the OH radicals seem to form an adduct with vanillin, _max at 430 nm and k(OH + V-OH) = 3.3 × 10⁹ dm³ mol^-1 s^-1, while at pH 9, the OH radical reaction resulted in the formation of vanillin phenoxyl radical with _max at 410 nm and k(OH + V-O-) = 6.6 × 10⁹ dm³ mol^-1 s^-1. The reactivity of NO₂radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of OH, N, NO radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl₃OO, CHCl₂OO and CH radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 × 10⁷ dm³ mol^-1 s^-1 indicate its antioxidative behaviour.     

Competitive Mechanism of the Nonbranched Radical Chain Oxidation of Hydrogen Involving the Free Cyclohydrotetraoxyl Radical [OO•••H•••OO]•, which Inhibits the Chain Process

A nonbranched radical chain mechanism, which does not pass into non-steady-state critical regimes, was proposed for the uncatalyzed oxidation of hydrogen. This mechanism includes competitive reactions with the participation of H, HO, and HO ₂ free radicals and the inactive cyclohydrotetraoxyl radical HO ₄ stabilized by inner hydrogen bonding, wherein the cyclohydrotetraoxyl radical inhibits the chain process. A simple rate equation, which describes the nonmonotonic (with a maximum) dependence of the rate of the nonbranched chain process of hydrogen peroxide and water formation on the concentration of molecular oxygen, was derived using the quasi-steady-state approximation. The nonchain reaction paths of free-radical hydrogen oxidation were considered. It was assumed that the cyclic free radical HO ₄ can be an intermediate in the series of conversions of biologically harmful energy of cosmic radiation in the upper atmosphere.     

Stability of the valinomycin-rubidium complex in water saturated nitrobenzene

From the extraction experiments and -activity measurements, the extraction constant corresponding to the Rb⁺(aq)+CsL⁺(nb)RbL⁺(nb)+Cs⁺(aq) equilibrium in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated in the form logK _ex (Rb⁺, CsL⁺)=0.9. Further, the stability constant of the valinomycin-rubidium complex in nitrobenzene saturated with water was calculated as log _nb(RbL⁺)=11.7.     

Crystal Structures and Magnetic Properties of Cu(II) Complexes with Pyrazole‐Substituted Iminonitroxyl Radicals: New Trinuclear Heterospin Complexes

The paper describes the crystal structures and magnetic properties of complexes of copper(II) hexafluoroacetate (Cu(hfac)₂) with stable pyrazolesubstituted iminonitroxyl radicals containing the pyrazole substitutuent in the second position of the 2imidazoline cycle (L). A new group of [Cu(hfac)₂]₃(L)₂ complexes is found, in which L performs a bidentatebridge function due to the coordination of the imine N atoms of the pyrazole and imidazoline cycles. It is shown that in the solid complexes there are Cu²⁺—N = C—N—O exchange routes with highenergy ferromagnetic interactions (60–100 cm^-1).     

Reactions of Peroxy Radicals with Hydrocarbons and Alcohols: Transition State Geometry and the Polar Effect

The reaction EtOO + EtH EtOOH + Et was studied by the intersecting parabolas method and calculated using density functional theory. The interatomic C–H, O–H, and C–O distances of the transition state for this reaction were calculated using these methods. The formulas for calculating these distances from experimental data were obtained. Similar calculations and comparisons were carried out for the reaction EtOO + MeCH₂OH EtOOH + MeCHOH. The polar effect of the hydroxy groups on the transition state manifested itself in a decrease in the activation energy and in the formation of a nonlinear structure of the transition state. An empirical formula for estimating the C–H–O angle in the transition state from the enthalpy and activation energy was derived.     

Dissociation equilibrium between uncharged and charged local anesthetic lidocaine in a surface-adsorbed film

The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH⁺) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality m_t at 0X₂0.5, where X₂ is the mole fraction of LC in the mixture, while they decreased rapidly with increasing m_t at 0.5<X₂1. It was shown from the pH measurements that almost all LC molecules were changed into LCH⁺ ions by protonation at 0X₂0.5 and both forms coexisted only at 0.5<X₂1. The quantities of the respective LC and LCH⁺ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH⁺ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH⁺ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH⁺ in the region at 0X₂0.5, (2) preferential partitioning of LC at 0.5<X₂<around 0.7, and (3) negative partitioning of LCH⁺ at around 0.7X₂1. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones.     

Enthalpies of formation of amidyl free radicals

The enthalpies of formation (#x0394;H°_f) of twenty-one amidyl radical (R) belonging to the formamidyl homological series were calculated using the published values of R—H bond dissociation energies. Among them, the H°_f values of nine radicals were first calculated and those of eight radicals were refined. Most of the H°_f values of corresponding starting molecules RH (H°_f(RH)) were obtained using the macroincrementing schemes. Based on the group additivity scheme, the structure—enthalpy of formation relationships for the radicals considered were examined, the H°_f(R) values were analyzed, and their reliability was confirmed. Parameters for calculating the H°_f values of radicals belonging to this homologous series were suggested.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1577, August, 2004.     

Nature of transient species formed during pulse radiolysis of 4-mercaptopyridine in aqueous solutions: Formation of a dimer radical species by one-electron reduction reaction

Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N₃ and Br₂ ^–, react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS /4-PyS^– was estimated to be 0.93V vs. NHE by equilibrium reaction with I₂ ^– /2I^– couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl₂ ^– and Br₂ ^– radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, e_aq ^– reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.     

Synthesis of γ-Fe2O3 by thermal decomposition of FeC4H4O6·2.5H2O

Iron(II) tartrate two and a half hydrate (FeC₄H₄O₆·2.5H₂O) was prepared and its thermal dehydration and decomposition were studied with a simultaneous thermal analyser (TG/DTA/DTG) under atmospheres of static air, dynamic dry nitrogen and dynamic air. This study was supplemented with the two-probe d.c. electrical conductivity technique under the same atmospheres. Under all the above atmospheres, the thermal dehydration was found to be a two-step process. However, the thermal decomposition process was quite complicated, involving the formation of various metastable intermediates, including-Fe₂O₃. The final product of decomposition under all atmosphere was-Fe₂O₃.Studies on the physical properties of-Fe₂O₃ were also undertaken.

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Zusammenfassung Es wurde Eisen(II)-tartrathydrat (FeC₄H₄O₆ · 2,5H₂O) hergestellt und seine thermische Dehydratation bzw. Zersetzung in statischer Luftatmosphäre bzw. im Stickstoff- und Luftstrom mittels eines Simultanthermoanalysators (TG/DTA/DTG) untersucht, ergänzt durch Untersuchungen nach dem Gleichstromleitfähigkeitsverfahren in den gleichen Atmosphären. Die thermische Dehydratation wurde in jedem Falle als zweistufig befunden. Der thermische Zersetzungsprozeß ist jedoch wegen der Bildung verschiedener metastabiler Zwischenprodukte, z. B.-Fe₂O₃, recht kompliziert. Das Endprodukt der Zersetzung war in allen Fällen-Fe₂O₃. Weiterhin wurden die physikalischen Eigenschaften von-Fe₂O₃ untersucht.

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, FeC₄H₄O₆ · 2,5₂. . , . , y-Fe₂O₃. -Fe₂O₃. -Fe₂O₃.

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Now deceased.

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Financial assistance for this work was given by Grants-in-aid (Defence Ministry), Govt. of India. One of the authors (A.V.R.) is grateful to the Head, Dept. of Chemistry, Sardar Patel University, for his interest and encouragement.     

New Molybdenum(V) Complexes Prepared by the Oxidation of Dinuclear Quadruply-Bonded Molybdenum(II) Monothiocarboxylates

Oxidation of molybdenum(II) thiopivalate and thiobenzoate in the presence of -picoline or pyridine results in the formation of dinuclear molybdenum(V) complexes of the general formulae [Mo₂O₂(-O)₂(-SO₄)L₄] with L = -picoline or pyridine and [Mo₂O₂(-O)(-S)(-SO₄)L₄] with L = -picoline. As determined by X-ray structure analysis, two complexes with -picoline differ in their bridging cores: In one complex, two Mo atoms are doubly bridged through two oxygen atoms; in the other, one Mo atom is doubly bridged through oxygen and sulfur atoms. However, they both crystallize together. The product is solvated with -picoline and water molecules. Molybdenum atoms exhibit distorted octahedral coordinations. The same complexes were prepared also through direct reactions of [Mo₂O₃(O₂CCH₃)₄] with thiopivalic and thiobenzoic acid in the presence of -picoline or pyridine. The appearance of the oxo-oxygens and sulfido-sulfur as well as sulfato ligand is explained by the molybdenum-catalyzed oxidation of thiocarboxylates.     

Structure of vanadium phosphate anion in solutions from17O,51V and31P NMR data

¹⁷O,⁵¹V and³¹P NMR studies indicate that the anion structure of sodium vanadophosphate in an aqueous solution is close to that in crystals of the (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O salt.

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¹⁷O,⁵¹V,³¹P , (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O.

     

Inclusion complexation of N-substituted phenothiazines and their radical cations generated electrochemically with <Emphasis Type="Italic">β</Emphasis>-cyclodextrin

The interactions of -cyclodextrin (-CD) with N-phenylphenothiazine (1), N-benzylphenothiazine (2) and N-phenethylphenothiazine (3) were studied by cyclic voltammetry. In aqueous solutions, increasing the amount of -CD caused negative shifts in the anodic peaks and an increase in the current of the 1/1 ⁺ and 3/3 ⁺ couples owing to the fact that more 1 and 3 were included in the -CD cavities. However, compound 2 neither gave an anodic nor a cathodic wave in the presence of -CD because the oxidization reactions on the surface of electrode were controlled by the conformations of the N-substituted phenothiazines in the cavity of -CD. In 1:9 methanol/water binary solutions, 1 and 3 were investigated by fast scan cyclic voltammetry which showed that the irreversible waves became quasi-reversible waves in the presence of -CD, confirmed the stabilization of cation radical intermediates by -CD. The electrochemical and absorption spectral data indicated 1:1 inclusion complex formation of -CD with 1 and 3 cation radicals in methanol/water binary solutions and the binding constants of 1 ⁺ and 3 ⁺ were very large under this condition.     

Support and mixing effect of an Fe2O3 catalyst for oxidative dehydrogenation of 1-butene

The support and mixing effects of Fe₂O₃ for the activity of 1-butene oxidative dehydrogenation were examined. Alumina and titania which were able to catalyze the isomerization of butene via an allyl intermediate, stimulated remarkably the formation of butadiene from butene when they were used as support or mixing component of Fe₂O₃ catalyst. Otherwise Fe₂O₃ supported on SO ₄ ^2– ion containing Al₂O₃ or TiO₂–Al₂O₃, which catalyze the isomerization via a cationic intermediate, is almost inactive for the formation of butadiene.

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Fe₂O₃ 1-. , , , Fe₂O₃. , Fe₂O₃, Al₂O₃, SO ₄ ^–2 , TiO₂–Al₂O₃, , .

     

Kinetic study of the thermal dehydration of layered [Ni2Al(OH)6]2SO4.nH 2O

The kinetics of thermal dehydration of [Ni₂Al(OH)₆]₂SO₄.nH₂O has been studied through the analysis of isothermal weight loss data. The results obtained seem to indicate that the process is governed by a diffusion mechanism up to an value which is dependent on the temperature. An explanation is provided for this behaviour on the basis of the structural properties of the compound and the nature of the water loss.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung von [Ni₂Al(OH)₆]₂SO₄.nH₂O wurde mittels isothermer TG untersucht. Die Ergebnisse scheinen darauf hinzudeuten, daß der Prozeß bis zu einem von der Temperatur abhängigen -Wert von einem Diffusionsmechanismus bestimmt wird. Für dieses Verhalten wird basierend auf den strukturellen Eigenschaften der Verbindung und der Natur der Wasserabgabe eine Erklärung gegeben.

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, [Ni₂Al(OH)₆]₂SO₄.nH₂O. , , . , .

     

A study of thermal preparation of iron (III) pigments by means of thermal analysis methods

The decomposition of hydronium jarosite occurs in two temperature ranges: first a loss of 8 moles of H₂O from 2 moles of jarosite, then in the second step one mole of H₂O and 4 moles of SO₃ are simultaneously evolved. Fe(OH)(SO₄)₂ and Fe₂O(SO₄)₂ are assumed intermediates. During the thermal treatment of Na or K jarosits, only Fe2(SO₄)₃ appears as intermediate. The decomposition temperatures are significantly influenced by the type of crucible used (determination of partial pressure of gaseous decomposition products). The particle size distribution of the starting jarosite has no effect upon the temperature of the decomposition steps and of the reaction with ZnO.The results of TG measurements were evaluated via calculations of the steps of the experimental activation energies for these partial decomposition jarosites and for their reaction with ZnO.

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Zusammenfassung Die Zersetzung von Hydronium-jarosit verläuft in zwei Stufen: (1) Abgabe von 8 Mol Wasser, (2) simultane Abspaltung von 1 Mol Wasser + 4 Mol SO₃/2 Mol Jarosit. Als Zwischenprodukte werden Fe(OH)(SO₄) und Fe₂O(SO₄)₂ vermutet. Bei der thermischen Zersetzung von Na- und K-Jarosit tritt nur Fe₂(SO₄)₃ als Zwischenprodukt auf.Die Zersetzungstemperaturen werden durch die Tiegelform erheblich beeinflusst (über den Partialdruck der gasförmigen Zersetzungsprodukte). Die Teilchengrössenverteilung des Ausgangs-Jarosits hat keinen Einfluss auf die Temperaturen der Zersetzungsschritte des Jarosits und der Reaktion mit ZnO. Aus den Ergebnissen der TG-Messungen werden experimentelle Aktivierungsenergien für die Zersetzungsreaktionen der Jarosite und ihre Umsetzung mit ZnO berechnet.

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- . 8 , — 4 . Fe(OH)SO₄ Fe₂O(SO₄)₂. Fe₂(SO₄)₃. , , . . .

     

Comparative kinetic and thermodynamic study on the chlorination of V2O5 with CCl4, COCl2 and Cl2

The chlorination kinetics of pure vanadia was studied via isothermal thermogravimetric measurements, with CCl₄, CoCl₂ and Cl₂ as chlorinating agents. At temperatures where chemical control was predominant, apparent activation energies of 77, 48 and 126 kJ: mol^–1 were obtained for chlorination by CCl₄, COCl₄ and Cl₂, respectively. For interpretation of the conversion vs. time curves in the whole conversion range, a non-uniform particle size distribution was assumed, where the reacting solid phase was considered to be composed of thin plates of different thicknesses. With this model, a fairly good correspondence was obtained between the measured and calculated kinetic curves. Selected thermodynamic calculation data on the V₂O₅ + CCl₄, V₂O₅ + COCl₂ and V₂O₅ + Cl₂ systems are presented.

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Zusammenfassung Mittels isothermen Thermogravimetriemessungen wurde die Kinetik der Chlorierung von reinem Vanadiumoxid mit CCl₄, COCl₂ und Cl₂ als Chlorierungsmittel untersucht. Bei Temperaturen mit vorherrschender chemischer Kontrolle wurde für die Chlorierung mit CCl₄, COCl₂ bzw. Cl₂ Bruttoaktivierungsenergien von 77, 48 bzw. 126 kJ/mol erhalten. Zur Interpretation der Konversion-Zeit-Diagramme im gesamten Conversionsbereich wurde eine nichteinheitliche Teilchengrösseverteilung angenommen, namentlich den Bestand der reagierenden Festphase aus dünnen Plättchen unterschiedlicher Dicke. Mit diesem Modell konnte eine recht gute Übereinstimmung zwischen errechneten und ermittelten kinetischen Kurven erhalten werden. Einige thermodynamische Rechenbeispiele für die Systeme V₂O₅ + CCl₄, V₂O₅ + COCl₂ und V₂O₅+Cl₂ wurden gegeben.

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, l₄, l₂ l₂. , l₄, l₂ l₂, 77, 48 126 ·^–1. — , . , . - . V₂O₅+CCl₄, V₂O₅+COCl₂ V₂O₅+Cl₂.

     

Redox reactions of basic fuchsin in homogeneous aqueous media

The pulse-radiolysis technique has been employed to understand the reaction mechanism and to characterize the transient species involved in the redox processes taking place in the radiation chemistry of basic fuchsin (BF⁺). One-electron reduction and oxidation reactions of BF⁺ have been carried out in homogeneous aqueous solutions employing various reducing (e _aq ^– , (CH₃)₂COH, CO ₂ ^– ) and oxidizing (N ₃, Br, Cl ₂ ^– Br ₂ ^– ) radicals. The absorption spectra of the transients formed in the above reactions have been attributed to semi-reduced and semi-oxidized species of BF⁺, respectively. The kinetic and spectroscopic properties of these transients have been evaluated. The reaction with H and OH radicals have also been performed and compared with those of specific one-electron reducing and oxidizing radicals. These reactions have been inferred predominantly by addition to BF⁺. Protolytic equilibria involving semi-reduced species of basic fuchsin have been studied over the pH range from 2 to 10 and the pK _a has been determined to be 3.9.     

On the Role of Surface Forces in Contact Interaction between Elastic Sphere and Hard Surface

The works preformed earlier were reviewed briefly, and the new problem of the contact interaction between the elastic sphere and hard surface was formulated. The solution of a problem to the generalized surface force and its contact and noncontact components was obtained. The specific case of the obtained solution, when the separation = 0, was considered. The existence of two states of contact interaction between the elastic sphere and hard plane was revealed at = 0: (i) the stable state, at contact with the neck of radius a ₁= , where Ris the sphere radius, = (1 – )/(E), Eis the modulus of elasticity of the sphere, is its Poisson's coefficient, and () is the specific energy of adhesion of the surfaces at the lowest possible separation between these surfaces; and (ii) the unstable (metastable) state, at contact with radius a ₂= 0, i.e., at the point contact between the sphere and the plane. In this case, however, the stable contact with the neck at 0 when the modulus of elasticity E , i.e., at the interaction between the hard sphere and hard plane, is also degenerated into the point contact. It was shown that at the point contact, the contact component F _s ^"of the generalized surface force F _svanishes, whereas the noncontact component F _s ^"acquires the value F _s ^"= F _s= 2R() equal to the force of adhesion.     

Reactivity and flexibility in platinum metal clusters

The synthesis, structural properties, and fluxional behaviour of platinum-triosmium and platinum-triruthenium clusters derived from Os₃Pt(-H)₂ (CO)₁₀(PR₃) and Ru₃Pt(-H)(-CC ^t Bu)(CO)₉ (dppe) and related species are described.