Isomer conversions in perfluoro-1-ethylindane under the action of antimony pentafluoride

Perfluoro-1-ethylindane on heating with SbF₅ is isomerized to perfluoro-1,1-dimethylindane, perfluoro-,-o-trimethylstyrene, and perfluoro-1,2-dimethylindane. In the presence of SbF₅, the latter two products are converted one into the other. In addition, in SbF₅ perfluoro-1,2-dimethylindane is defluorinated to perfluoro-2,3-dimethylindene and fluorinated to perfluoro-2,3-dimethyl-4,5,6,7-tetrahydroindene which is further fluorinated to perfluoro-1,2-dimethyl-4,5,6,7-tetrahydroindane and is converted at 200C to perfluoro-1,7-dimethylindane. The latter is also formed on heating perfluoro-,-o-trimethylstyrene with SbF₅ at 200C.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 645–652, March, 1990.     

Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G^*(6D) basis set. Least-squares refinement of a model withC _s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, =119.0±0.2 (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1, 120.7±0.1, and 119.0±0.3, respectively. Important bond distances are r _g(C-C)=1.398±0.003 å andr _g(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is ¦¦=44±4. The equilibrium dihedral angle is calculated to be 41.8 at the HF level and 43.6 at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(C_ortho-C_meta) -r(C_ipso-C_ortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.     

Thermal investigation of the basic copper(II) nitrate Cu(OH)1.5(NO3)0.5

A thermal investigation of basic copper(II) nitrate was made under dynamic heating conditions as well as in an isothermal environment. Data analysis was applied to calculate the heat of thermal decomposition of gerhardtite (21.6±0.1 kcal/mole), which does not depend on the heating rate from 4/min to 20/min.     

Molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide from gas-phase electron diffraction

The molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide has been determined by electron diffraction in the gas phase. The experimental data are consistent withC _s molecular symmetry and boat conformation with a flattened end at the silicon atom. The flap angles characterizing the orientation of C-Si-C and C-O-C planes with respect to the four coplanar carbon atoms of the ring are 16.6 ± 0.6 and 73.3 ± 0.6, respectively. Bond lengths (r_g) are Si-C₆, 1.866 ±0.008; Si-C₂, 1.899 ± 0.008; C₂-C₃, 1.513 ± 0.005; C₃-C₄ (bridge), 1.477 ± 0.013; C-O, 1.443 ± 0.007; (C-H)_mean 1.116 ± 0.003 å. Bond angles are <C₅-Si-C₂, 96.2 ± 0.4; <Si-C₂-C₃, 103.9 ± 0.3; <C₂-C₃-C₄, 116.5 ± 0.3; <C₃-C₄-O, 59.2 ± 0.5; zC₄-C₃-H₉, 109.0 ± 3.5; <C₂-C₃-H₉, 132.9 ± 3.1; <C₆-Si-C₁₂, 114.6 ± 0.8; <Si-C₆-H₁₅, 109.7 ± 0.9.     

Thermal changes in decahydro-closo-decaborate(2-)copper(I) Cu2B10H10 and the nature of copper borides

Thermal changes in Cu₂B₁₀H₁₀ have been studied over the temperature range 25–800C using DTA, gas-volume, IR-spectroscopic, and x-ray phase analytical methods. Decomposition of the salt starts at 290C and is accompanied by formation of amorphous and crystalline phases of CuB₂₄, Cu, and B_am. A crystalline copper phase starts to form at 290C.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 503–506, March, 1990.     

Free radicals in γ-irradiated olefinic silica compounds

Results are reported from -irradiation of compounds of structure . each of which gives a characteristic ESR spectrum having a hyperfine structure whose resolution is somewhat reduced by the coupling of the radical to the silica. The splittings are 23–25 Oe (typical of alkyl radicals), except for the phenyl compound. Improved resolution is provided by varying the temperature between –196 and 20C. The bond to the surface gives the radical high thermal stability; contact with air at 20C converts the alkyl radicals to peroxyl ones. Hyperfine splitting from the hydrogen H_p 5000 Oe is observed in all compounds except.     

Kinetics and mechanism of the interaction of thiourea with cis-diaquaethylene-diamineplatinum(II) perchlorate in aqueous medium

The kinetics of the interaction of thiourea with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [thiourea] and temperature at a particular pH(4.0), where the substrate complex exists predominantly as the diaqua species and the thiourea ligand as a neutral molecule. The reaction proceeds via a rapid outer sphere association followed by two slow consecutive steps, the second step exhibiting first order dependence on the aqua ion and thiourea concentrations. The activation parameters for both the steps have been evaluated: (H ₁ = 54.8 ± 1.2 kJ mol^–1, S ₁ = –96 ± 4 J K^–1 mol^–1, H ₂ = 27.9 ± 0.8 kJ mol^–1 and, S ₂ = –183 ± 2.6 J K^–1 mol^–1). The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both consecutive steps.     

Effect of the chemical nature of the support on the properties of platinum catalysts for the combined oxidation of CO and H2

The steady-state rate of hydrogen oxidation catalyzed by platinum on an inert support (corundum) is greater than the rate of oxidation of carbon monoxide, while the rate of hydrogen oxidation on a platinum-vanadium catalyst is less than the rate of oxidation of carbon monoxide. The conditions for the complete selective oxidation of the reaction mixture components were determined. Hydrogen is oxidized on the Pt/corundum cataljst at 273K in a non-steady-state mode, while CO is oxidized on the same catalyst at 273 K and on Pt/BaSO₄-V₂O₅ at 383–393K in a steady-state mode.Deceased.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 31, No. 2, pp. 81–85, March–April, 1995.     

Effect of sodium oxide doping on solid-solid interactions between V2O5 AND Al2O3

A V₂O₅/Al₂O₃ mixed solids sample was prepared with a molar ratio of 0.41 Na₂O (4 and 10 mol%) was added in the form of sodium nitrate prior to calcination in air in the temperature range 500–1000C. Solid-solid interactions between V₂O₅ and Al₂O₃ were studied using DTA and TG curves and their derivatives together with XRD techniques.The results obtained showed that Na₂O interacted with V₂O₅ at temperatures starting from 500C to yield a sodium/vanadium compound, Na_0.3V₂O₅ which remained stable and decomposed in part by heating at 1000C. V₂O₅ exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol% of Na₂O and preheated at 500C, and in monoclinic form in the case of the mixed solid doped with 10 mol% of Na₂O.Heating of pure and doped mixed oxide solids at 650C resulted in the conversion of most of the V₂O₅ into AlVO₄. Doping with sodium oxide enhanced the solid-solid interaction between V₂O₅ and Al₂O₃ at 650C to produce AlVO₄. The produced AlVO₄ decomposed completely on heating at 700C to form -Al₂O₃ and V₂O₅, (orthorhombic and monoclinic forms).The presence of Na₂O was found to decrease the relative intensity of the diffraction lines of -Al₂O₃ (corundum) produced at 750C which indicated some kind of hindrance of the crystallization process.Heating of pure and doped mixed solids at 1000C resulted in a further crystallization of acorundum together with V₂O₅ and sodium vanadate, Na_0.3V₂O₅. However, the intensities of diffraction lines relative to those of the sodium vanadium compound were found to decrease markedly by heating at 1000C, indicating partial thermal decomposition into vanadium and aluminium oxides.     

The interaction of 2, 6-di-tert-butyl-4-butoxyphenoxyl and diphenylnitrogen radicals with molecules containing N-H and O-H bonds

It has been shown by the EPR method that the thermal decomposition of bis-(1, 3, 5-tri-tert-butyl-cyclohexadien-2, 5-one)-peroxide (I) into 2, 6-di-tert-butyl-4-butoxyphenoxyl radicals (II) in xylene solution at 80–100 C follows first order kinetics. The transfer of hydrogen from the molecule of diphenylamine (DPA) and 2, 6-di-tert-butyl-4-methylphenol (ionol) to the radicals of (II) formed by the decomposition of (I) has been established and investigated.The diphenylnitrogen (DPN) radicals formed by the thermal dissociation of tetraphenylhydrazine (TPH) in organic solvents at 100 C split a hydrogen atom from the hydroxyl group of sterically hindered phenols, leading to the formation of the corresponding phenoxyl radicals.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

Kinetics and mechanisms of the oxidation of the octacyanoniobate(III)ion by oxyanions in alkaline aqueous media

Summary The kinetics and mechanisms of the oxidation of Nb(CN) _inf8 ^sup5– by the oxyanions S₂O _inf8 ^sup2– , BrO _inf3 ^sup– , and IO _inf4 ^sup– have been investigated in alkaline aqueous media (pH 12). The second-order rate constant for the electron transfer reaction between Nb(CN) _inf8 ^sup5– and S₂O _inf8 ^sup2– at 25.0 °C, I = 0.36m (K⁺), is 11.1± 0.3 m ^–1 s ^–1 with H = 30 ± 2kJmol^–1 and S = - 125 + 7JK^–1 mol^–1. The rate constant for the oxidation of Nb(CN) _inf8 ^sup5– by BrO _inf3 ^sup– at 25.0 °C, I = 0.20m (Na⁺), is 2.39 ± 0.08m ^–1 s ^–1 with H = 28 ± 2kJmol^–1 and S = -139 ± 7JK^–1mol^–1. The oxidation of Nb(CN) _inf8 ^sup5– by IO _inf4 ^sup– proceeds by two parallel pathways involving the monomeric IO _inf4 ^sup– ion and the hydrated dimer H₂I₂O _inf10 ^sup4– . The second-order rate constant for the oxidation of Nb(CN) _inf8 ^sup5– by monomeric IO _inf4 ^sup– at 5.0 °C, I = 0.050m (Na⁺), is (3.3 ± 0.6) × 10³ m ^–1 s ^–1 with H = 75 ± 6 kJ mol^–1 and S = 94 ± 15 J K^–1 mol^–1, while the rate constant for the oxidation by H₂I₂O _inf10 ^sup4– is (1.8 ± 0.1) × 10³ m ^–1 s ^–1 with H = 97 ± 5 kJ mol^–1 and S = 166 ± 16 J K^–1 mol^–1 under the same reaction conditions. The rate constants for each of the oxidants employed display specific cation catalysis with the order of increasing rate constants: Li⁺ < Na+ < NH _inf4 ^sup+ < K⁺ < Rb⁺ < Cs⁺, in the same direction as the electronic polarizability of the cations. The results are discussed in terms of the outer-sphere electron-transfer processes and compared with the corresponding data and mechanisms reported for other metal-cyano reductants.     

Kinetics and mechanism of the oxidation of acetaldehyde by chromic acid in perchloric acid

Summary The oxidation of MeCHO by chromium(VI) has been studied in HClO₄ medium over a wide range of experimental conditions and has been found to obey the rate law;v=k[MeCHO][HCrO ₄ ^– ][H⁺]. The calculated H and-S values for the reaction are 30±2kJ mol^–1 and 171±7J mol^–1deg^–1, respectively. The mechanism is discussed in terms of carbon-hydrogen bond cleavage.     

Thermochemical characterization of phenolic resins

Phenol-formaldehyde resins (I andII), synthesised at a monomer feed ratio of F/P = 1.0 and 1.5, were cured at 130C for 48 h without any catalyst (Ia, IIa), with 0.1% ferric acetyl acetonate (Ib, IIb) and with 0.1 %p-toluenesulphonic acid (Ic, IIc). Thermogravimetric studies indicate that the decomposition of the cured products takes place in two distinct stages: The first stage (T=340–480C; =0.045–0.16; E ₁ = 140±10-239±24 and 60±3–65±2 kJ mol^–1 for seriesI andII respectively) was attributed to the predominant cleavage of formal linkages. The main stage decomposition (T=460–640C; =0.114–0.393; E ₂=115±8–169±8 and 91±6–103±7 kJ mol^–1 for seriesI andII respectively) was attributed to reactions leading to graphitisation. E ₂ values were correlated to the extent of cure as measured by IR spectroscopy and pyrolysis-GC. The effect of catalysts on the extent of cure and on the activation energy was evaluated.The authors are grateful to Dr. S. Ganapathy, NCL, Pune for providing solid state NMR, Dr. K. Krishnan and Dr. A. G. Rajendran, VSSC, Trivandrum for thermoanalytical measurements.     

Molecular structure of N-(2-hydroxyethyl)pyridinium bromide

X-ray diffraction, structural analysis was employed to establish the structure of N-(2-hydroxyethyl)pyridinium bromide, C₇H₁₀NO⁺-Br^–. The plane of the pyridinium ring is twisted by 93 relative to the C-C bond of the side-chain. The N-C-C-O torsion angle is 63.6. The OH bond is oriented toward the heteroaromatic ring. The H-O-C-C torsion angle is 84.4. The molecular packing in the crystal lattice is such that the bromide ions are found between the heteroaromatic rings and the hydrogen bonded to the hydroxyl groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2617–2619, November, 1990.     

Metal ion catalysed aquation of carboxylatoamine cobalt(III) complexes. Kinetics of copper(II) catalysed aquation ofcis(diformato)bis(ethylenediamine)cobalt(III) ion

Summary The aquation ofcis-[(en)₂Co(CO₂H)₂]⁺ tocis-[(en)₂Co(OH₂)(CO₂H)]²⁺ is catalysed by Cu²⁺ and the rate equation, –d[complex]_t/dt=(k_Cu[Cu²⁺]+k_H [H⁺]) [complex)_T is valid at [Cu²⁺]_T=0.01–0.1, I=0.5 and [HClO₄]=0.005 mol dm^–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu²⁺ and H⁺-catalysed paths are: k_H(35°C)=(2.44±0.09)×10^–2 dm³ mol^–1 s^–1, H=83±13 kJ mol^–1, S=–8±42 JK^–1 mol^–1, k _Cu (35°C)=(3.30±0.09)×10^–3 dm³ mol^–1 s^–1, H=73.2±6.1 kJ mol^–1, S=–55±20 JK^–1 mol^–1. The formate-bridged innersphere binuclear complex,cis-[(en)₂Co{(O₂CH)₂Cu}]³⁺ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H⁺-bridged species presumed to be present in the acidcatalysed path.     

Synthesis,metal-exchange kinetics and X-ray structure of the nickel(II) complex of the diazacyclam ligand 1,3,6,10,12,15-hexa-azatricyclo [13.3.1.16,10]eicosane, [NiL] (ClO4)2

The preparation of the nickel(II) complex of the diazacyclam ligand 1,3,6,10,12,15-hexaazatricyclo [13.3.1.16,10]eicosane (2) by the reaction of the nickel(II) complex of N-(2-aminoethyl)-1,3-diaminopropane with formaldehyde in MeOH solution is described. The crystal structure of [NiL](ClO4)2 has been determined. The nickel atom is four coordinate and planar with Ni-N bond lengths of 1.969(4) and 1.928(3)Å in a centrosymmetric structure. The basic diazacyclam ring system has a trans III configuration with the two additional six-membered rings fused in a chair conformation.The kinetics of the metal exchange:for the nickel complexes (1) and (2) have been studied in detail. Under the experimental conditions employed, with copper(II) in at least a tenfold excess, the reaction is independent of the copper(II) concentration. The copper(II) effectively scavenges the free ligand as the nickel(II) complex dissociates. For the nickel complex (1) k = 2 × 10–4 s–1 at 60°C and H = 126 ± 5 kJmol–1 and S298 = 61 ± 15 JK–1mol–1. For the complex (2), k = 1.8 × 10–4 s–1 at 60°C and H = 99 ± 6 kJmol–1 and S298 = –21 ± 10 JK–1 mol–1.     

The mechanisms of the acid-catalysed dissociation of tris-β-diketonatoruthenium(III) complexes

Summary The reactions of four -diketonatoruthenium(III) complexes in the presence of HNO₃ andp-MeC₆H₄SO₃H in the 45° and 57° range were followed spectrophotometrically in Me₂COH₂O mixtures. Dissociation of Ru(acac)₃ follows [H⁺]-dependent and [H⁺]²-dependent paths, whereas the bzac and F₃acacF₃ complexes follow only the [H⁺]-dependent path. The bzbz (Dibenzoylmethanate) complex is inert. Protonation of the bound ligand leads to its rupture from the metal ion. The bzac complex is kinetically more inert than the acac complex, because of extra stability arising from interaction of the (bzac) benzene ring with the pseudo-aromatic diketonate ring of the complex. Considering the kinetic labilities, the complexes may be arranged in the order Ru(F₃acacF₃)₃>Ru(acac)₃>Ru(bzac)₃>Ru(bzbz)₃.Activation parameters for [H⁺] dependent path are: H ₁ 86.5±7, 69±5, 121±7 kJ mol^–1, S ₂ –52±10, –107±10, 57±8 JK^–1 mol^–1 for acac, bzac and F₃acacF₃ complexes respectively and H ₂ 67±5 kJ mol^–1, S ₂ –92±8 JK^–1 mol^–1 for the acac complex only.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

Chemical interactions in the systems BaCuO2-PbO and YBa2Cu3O7-PbO

Chemical interactions were found to occur in the systems BaCuO₂-PbO and YBa₂Cu₃O₇-PbO at 600–800C. The chemical peculiarities of these reactions are explained on the basis of redox transformations, with formation of the phase BaPbO₃.

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Zusammenfassung Bei 600–800C konnte im System BaCuO₂-PbO und YBa₂Cu₃O₇-PbO eine chemische Wechselwirkung festgestellt werden. Die chemische Besonderheit der Reaktionen wurde mit Hilfe von Redoxumformungen unter Bildung der Phase BaPbO₃ erklÄrt.