Studies on some radical transfer reactions by entrapping the radicals as polymer endgroups. III. Reaction of ȮH radical with halide ions

The reactions of OH radical with Cl^?, Br^?, I^?, and F^? ions have been studied by entrapping the product radicals as polymer endgroup which have been detected and estimated by the sensitive dye partition technique. The rate constants of the reactions with Br^?, Cl^?, and F^? ions have been determined to be 1.51 × 10⁹, 1.32 × 10⁹, and 0.92 × 10⁹ L mol^?1 s^?1, respectively at 25°C and pH 1.00. Oxidation of I^? ions liberates I, which inhibits the polymerization and the reaction could not be followed by polymer endgroup analysis. The observed order of reactivity Br^? > Cl^? > F^? is in accordance with the electron affinities of the halide ions. The acidity of the reaction medium has a strong influence on the rate of reaction. With Br^? ions, the rate constant of the reaction falls from 1.51 × 10⁹ to 0.75 × 10⁹ L mol^?1 s^?1 at 25°C as the pH is raised from 1.0 to 2.8. The method is simple and accurate and can be applied to study very reactive radicals.     

Excess heat capacities and orientational order in systems containing hexadecane isomers of different molecular structure

Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec _p ^E values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc _p ^E are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C₁₆ isomers. The excess enthalpy and entropy vary with the C₁₆ isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C₁₆ isomers.     

The spectrophotometry and solvent-extraction behaviour of iron(III), vanadium(IV and V) and titanium(IV) chelates of 1-(o-carboxyphenyl)-3-hydroxy-3-methyltriazene

l-(o-Carboxyphenyl)-3-hydroxy-3-methyltriazene is proposed as an excellent reagent for the spectrophotometric determination of iron(III) and titanium(IV), and also for the separation of titanium from a large quantity of iron as well as other cations and anions. Iron(III) forms an anionic violet 1:2 complex at pH 4.0–9.4, and a cationic green 1:1 complex at pH 1.5–2.0, with absorption maxima at 570 nm and 660 nm, respectively. The violet complex is quantitatively extracted in chloroform containing n-octylamine at pH 3.0–9.0. The green and the violet iron(III) complexes obey Beer's law, the respective optimal ranges being 8.9–35.8 and 3.9–11.2 p.p.m. The yellow titanium chelate extracted into chloroform (absorption maximum at 410 nm) between pH 1.0 and 3.5, can be re-extracted into concentrated sulphuric acid a violet colour being produced with absorption maximum at 530 nm. Beer's law is obeyed in the ranges 0.8–5.7 p.p.m. for the titanium complex in chloroform and 3.4–19.2 p.p.m. when extracted in concentrated sulphuric acid. Interferences from diverse ions are not severe. Procedures for the separation and determination of titanium in the presence of a large quantity of iron are given. The isolation of the iron(III) and vanadium(IV and V) complexes, and their properties, are described.     

Separation of molybdenum from tungsten with di(2-ethylhexyl)-phosphoric acid ac extractant

The use of di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of molybdenum from tungsten was examined with the help of molybdenum-99 and tungsten-187 as radiotracers. Effective separation was obtained when the aqueous phase contained phosphoric acid at pH 0.8–2 or pH 3–3.5, depending on the amounts of metal. The method is applicable to both tracer and milligram amounts of molybdenum. The structure of the extracted species was examined by infrared spectroscopy.     

Physico-chemical properties of catalysts: Thermal analysis,infrared spectroscopy,X-ray diffraction and magnetic susceptibility of the vanadates of zinc,manganese and silver

Thermal characteristics of the vanadates of zinc, manganese and silver have been studied by DTA and TG techniques and the different transition products thus obtained have been characterised by IR, X-ray diffraction and magnetic susceptibility data. Chemical analyses indicate the following compositions of these vanadates: (1) Zn₂V₂O₇.5H₂O, (2) Zn₃(VO₄)₂.3H₂O, (3) Mn(VO₃)₂.2H₂O and (4) Ag₃VO₄. The DTA curves indicate that zinc pyrovanadate undergoes endothermic changes at 110–195, 265, 365, 440, 660° and one exothermic change at 485°. This system is diamagnetic which becomes completely paramagnetic after 660°. Zinc orthovanadate exhibits a number of endothermic peaks at 300, 470, 700, 815 and 930° respectively. This system is feebly paramagnetic and retains this property up to 930°. Manganese metavanadate undergoes endothermic changes at 240, 280–590, 830 and 880° respectively. This vanadate is paramagnetic and paramagnetism increases appreciably at 590° and remains constant up 830°. Silver orthovanadate exhibits three endothermic changes at 180, 455 and 640°, respectively.

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Zusammenfassung Die thermischen Charakteristika der Vanadate von Zink, Mangan und Silber wurden durch DTA- und TG-Methoden untersucht und die auf diese Weise erhaltenen verschiedenen Übergangsprodukte durch Daten aus IR-, Röntgen- und magnetischer Susceptibilität charakterisiert. Die chemische Analyse deutet auf folgende Zusammensetzung dieser Vanadate: 1) Zn₂V₂O₇.5H₂O, 2) Zn₃(VO₄)₂.3H₂O, 3) Mn(VO₃)₂.2H₂O und 4) Ag₃VO₄. Die DTA-Kurven zeigen endotherme Veränderungen des Zink-pyrovanadats bei 110–195, 265, 365, 440 und 660° und eine exotherme Veränderung bei 485°. Dieses System ist diamagnetisch und wird nach 660° vollständig paramagnetisch. Zink-orthovanadat zeigt eine Anzahl exothermer Peaks bei 300, 470, 700, 815, bzw. 930°. Dieses System ist schwach paramagnetisch und behält diese Eigenschaft bis zu 930°. Im Manganmetavanadat vollziehen sich endotherme Veränderungen bei 240, 280–590, 830 und 880°. Dieses Vanadat is paramagnetisch, der Pararnagnetismus steigt zusehends bei 590° und bleibt bis zu 830° konstant. Silberorthovanadat zeigt drei endotherme Veränderungen bei 180, 455 bzw. 640°.

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Résumé On a étudié par ATD et TG les caractéristiques thermiques des vanadates de zinc, de manganèse et d'argent. La caractérisation des divers produits de transition ainsi obtenus a été effectuée à partir des données fournies par IR, rayons X et susceptibilité magnétique. Les analyses chimiques indiquent les compositions suivantes de ces vanadates: (1) Zn₂V₂O₇.5H₂O, (2) Zn₃(VO₄)₂.3H₂O, (3) Mn(VO₃)₂.2H₂O et (4) Ag₃VO₄. Les courbes ATD du pyrovanadate de zinc montrent des effets endothermiques à 110–195, 265, 365, 440 et 660° ainsi qu'un phénomène exothermique à 485°. Ce corps est diamagnétique; il devient complètement paramagnétique au-dessus de 660°. L'orthovanadate de zinc donne des pics endothermiques à 300, 470, 700, 815 et 930°. Il est faiblement paramagnétique jusqu'à 930°. Le métavanadate de manganèse est le siège de phénomènes endothermiques à 240, 280–590, 830 et 880°. Il est paramagnétique et son paramagnétisme augmente de manière appréciable à 590° pour rester constant jusqu'à 830°. L'orthovanadate d'argent montre trois effets endothermiques à 180, 455 et 640°.

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, . - , . : Zn₂V₂O₇·5H₂O, Zn₃(VO₄)₂ · 3H₂O, Mn(VO₃)₂· 2H₂O Ag₃VO₄. , 110–195°, 265, 365,440 660° 485°. , 660° . 300, 470, 700, 815 930°. 930°. 240, 280–590, 830 880°. , 590° 830°. 180, 455 640°.

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The authors are grateful to the Physical Research Wing and Catalyst Research and Development Section, F. C. I., Sindri and also the Analytical Physics Division and Catalyst Section, I.I.P., Dehradun (India) for their help in getting TG and X-ray patterns of the catalysts studied.     

Spectroscopic and structural features of small thiocarbonyl molecules in low-lying excited states: Further applications of a variant of the orthogonal gradient method

Structural parameters of a set of five thiocarbonyl molecules in the lowest nπ* states are calculated by using a generalized orbital optimization algorithm (a variant of the orthogonal gradient method) in an INDO MCSCF framework. Transition energies, singlet-triplet splittings, planar inversion barriers, and dipole moments in nπ* states of different spin multiplicities are reported. Predicted structural features agree reasonably well with available experimental or theoretical data. Some interesting trends are noted in the computed inversion barrier heights, singlet-triplet splittings, and dipole moments in nπ* states.     

Error in an approximate wave function and an error minimization scheme

An estimate of error in an approximate wave function for a stationary state is put forward that does not require any information about the exact state. The measure is sensitive and direct. Parameters embedded in a trial wave function can be varied to minimize this error as well, leading to a variational principle. Such a scheme works nicely for bound states and the more so for Siegert states, for which the standard energy minimization principle does not apply. Pilot calculations on the anharmonic oscillator system and the radial Stark effect in the hydrogen atom reveal the worth of the endeavor. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Simultaneous determinations of a monofluorinated imidazo[1, 5-a] [1, 4] benzodiazepine and the corresponding benzophenone as a function of pH and in aqueous formulations by 19F nuclear magnetic resonance spectrometry

8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1, 5-a] [1, 4 ]benzodiazepine (called “midazolam”) exists in equilibrium with the corresponding benzophenone (the“open-Mng form”). The two compounds were determined simultaneously as a function of pH with ¹⁹F-n.m.r. spectrometry. In a unique application of ¹⁹F-n.m.r. spectrometry, the compounds are determined simultaneously in aqueous dosage forms without the need for sample preparation. The optimum signal-to-noise ratio for the major compound for the lowest concentration of sample used (≈ 1 mg ml^-1) was 200:1 for 3000 scans. This was obtained by partial proton decoupling and exponential multiplication of the free induction decay with a line-broadening parameter of 12 Hz. Quantitative results are presented with a standard deviation of < 2.0% in the mean ratio of the two compounds. The results are also compared with those obtained by the spectrophotometric fluorescamine method. Advantages of the ¹⁹F-n.m.r. technique in this determination are discussed.     

Reductive nitrosylation of tetraoxometallates—XVII. Molybdate-hydroxylamine-cyanide reaction, and synthesis and characterization of K2[Mo(NO)(CN)5] and (NMe4)2[Mo(NO)(CN)4]

A reaction condition is established which determines the nature of the products in the molybdate-hydroxylamine-cyanide reaction. With hydroxylamine always used in excess, it is the hydroxyl ion concentration of the reaction mixture which plays a vital role in determining whether K₄[Mo(NO)(CN)₅] or K₂[Mo(NO)(CN)₅] is obtained exclusively. The latter product is hereby reported for the first time. Its powder diffractogram being typical of a cubic system, a gross structural characterization has been made possible. The former under aqueous, aerobic conditions yields a new product, (NMe₄)₂[Mo(NO)(CN)₄].     

Yrast excitations in129Te

Using an 11.4MeV/u¹³⁶Xe beam of the UNILAC accelerator of GSI and a^natW target, A=184 isobars were produced and separated by using an on-line mass separator. A new isomeric state was found in¹⁸⁴Hf. This state decays with a half-life of 48(10) s and emits three -rays of 73, 482, and 555 keV as well as lower-lying cascade transitions. The hindrance of the 73 keV-E1 transition with K=8 is compared with those of other even-even hafnium isotopes. The half-life of¹⁸⁴Lu was estimated to be between 15 and 25s.