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891.
The oxidation of Na4Fe(CN)6 complex by S2O anion was found to follow an outer‐sphere electron transfer mechanism. We firstly carried out the reaction at pH=1. The specific rate constants of the reaction, kox, are (8.1±0.07)×10?2 and (4.3±0.1)×10?2 mol?1·L·s?1 at μ=1.0 mol·L?1 NaClO4, T=298 K for pH=1 (0.1 mol·L?1 HCl04) and 8, respectively. The activation parameters, obtained by measuring the rate constants of oxidation 283–303 K, were ΔH≠=(69.0±5.6) kJ·mol?1, ΔS≠=(?0.34±0.041)×102 J·mol?1·K?1 at pH=l and ΔH≠=(41.3±5.5) kJ·mol?1, ΔS≠=(?1.27±0.33)×102 J·mol?1·K?1 at pH=8, respectively. The cyclic voltammetry of Fe(CN) shows that the oxidation is a one‐electron reversible redox process with E1/2 values of 0.55 and 0.46 V vs. normal hydrogen electrode at μ=1.0 mol·L?1 LiClO4, for pH=1 and pH=8 (Tris). respectively. The kinetic results were discussed on the basis of Marcus theory. 相似文献
892.
Cs5[Na{W4N10}] was prepared from a mixture of NaNH2, CsNH2 and tungsten powder (molar ration 1 : 10 : 4) at 700°C in autoclaves. After the reaction is finished the nitride is embedded in an alkali metal matrix. Dark red crystals were isolated by washing out the alkali metal with liquid ammonia at room temperature. The structure of Cs5[Na{W4N10}] was solved by X-ray single crystal data: I41 (No. 80), Z = 4, a = 13.926(3) Å, c = 8.723(3) Å, Z(F) ≥ 3σ(F) = 1535, Z(Variables) = 63, R/Rw = 0.040/0.052. The compound is highly sensitive against moisture giving oxotungstates and ammonia. It contains a framework of tetrahedra [WNN3/21.5?]. Sodium shares four terminal nitrogen ligands. Including sodium a distorted, β-cristobalite type arrangement [Na{W4N10}5?] results. It contains caesium in all interstices formed by twelve nitrogen ligands in so-called Friauf polyhedra. 相似文献
893.
RAHMAN Nafisur SINGH Manisha HODA Nasrul Md.ZAIDI S.M. Kashif R. BANU Naheed 《中国化学》2005,23(12):1611-1617
A simple sensitive and economical method for the determination of labetalol hydrochloride has been proposed, based on the reaction of labetalol with sodium nitroprusside and hydroxylamine hydrochloride in sodium dihydrogen phosphate-sodium hydroxide buffer solution of pH 12. The green-blue color produced due to the formation of a nitroso derivative has been measured at 695 nm. The Beer's range was obeyed in the concentration range of 2-51 μg·mL^-1 with molar absorptivity of 0.48 × 10^4 L·mol^-1·cm^-1. Rigorous statistical analyses were performed for the validation of the method. A detailed investigation of the selectivity of the method has been done to find it to be highly selective for the determination of labetalol hydrochloride in the presence of its acidic degradation product and common excipients of formulations. The proposed method was successfully applied to the determination of labetalol hydrochloride in the laboratory prepared dosage forms. Comparison of the means of the proposed procedure with a reference method using point as well as interval hypotheses showed no statistically significant difference. The developed method was extended to investigate its applicability to biological samples. 相似文献
894.
Derek G. Leaist 《Journal of solution chemistry》1988,17(4):359-369
Diaphragm cells have been used to measure ternary diffusion coefficients for I2+NaI and I2+KI in aqueous solution at 25°C. Although most of the iodine molecules are bound to iodide ions and are transported as the triiodide species [I2(aq)+I–(aq)=I
3
–
(aq)], diffusion of the iodide salts produces relatively small countercurrent coupled flows of the iodine component. The ternary diffusivity of the iodine component in the solutions is 10 to 20% larger than the diffusivity of the triiodide species. This behavior can be understood by considering electrostatic coupling of the ionic flows. The diffusion equations for I2+NaI and I2+KI components are reformulated in terns of NaI3+NaI and KI3+KI mixed electrolyte components. 相似文献
895.
The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H2O)–1. The concentration dependence is described by the equation H=20.4537+1.0562m1/2-7.0568m+2.8659m3/2-0.3382m2 From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as Hc=9.98±0.16 kL-mol-1. The literature data on the solubility, activity and osmotic coefficients of NaNO3 at 25°C yielded a value of –9.98±0.38 kJ-mol–1. The good agreement between the experimental and calculated Hc values indicate the reliability of the input data. 相似文献
896.
Rycerz L. Cieślak-Golonka M. Ingier-Stocka E. Gaune-Escard M. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):231-239
Several experimental techniques were used to characterise the physicochemical properties of the TbBr3-NaBr system. The phase diagram determined by DSC, exhibits an eutectic and a Na3TbBr6 stoichiometric compound that decomposes peritectically (759 K) shortly after a solid-solid phase transition (745 K). The
eutectic composition, x(TbBr3)=39.5 mol%, was obtained from the Tamman method. This mixture melts at 699 K. With the corresponding enthalpy of about 16.1
kJ mol-1. Diffuse reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) confirmed
the existence of new phase exhibiting its own spectral characteristics, which may be possibly related to the formation of
Na3TbBr6 in this system. Additionally, the electrical conductivity of TbBr3-NaBr liquid mixtures was measured down to temperatures below solidification over the whole composition range.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
897.
本文以水热法合成的钛酸钠纳米管为前驱物,经过二次水热处理制备出了叶片状纯锐钛矿相TiO2晶体.采用高分辨TEM、XRD对晶体形貌和结构进行了分析.在纯水条件下,TiO2晶体长度达到1~2 μm,宽度100~200 nm,钛酸钠纳米管全部转化为锐钛矿相TiO2.pH值为11时,除了合成出微米级叶片状TiO2以外,还有少量未反应的钛酸钠纳米管以及由纳米管展开的膜片物,反映了钛酸钠纳米管向纯锐钛相叶片状TiO2转化的中间过程,显示在特定的水热条件下锐钛相TiO2和钛酸钠互相转化. 相似文献
898.
At 1050 ?C boron combines with sodium forming a boride of formerly unknown composition and crystal structure. The investigation of the homogeneous, monophasic, and crystalline powder was performed using X‐ray (23 ?C) and neutron (–271.5 ?C) diffraction methods. The structure solution led to an unusual arrangement of boron atoms, characterized by two different types of polyhedra, a distorted pentagonal bipyramid and a distorted octahedron. The Rietveld refinement of the crystal structure was carried out in the orthorhombic space group Cmmm (X‐ray: a = 18.6945(6) Å, b = 5.7009(2) Å, c = 4.1506(1) Å, V = 442.35(1) Å3, Z = 2; Rwp = 0.087, Rp = 0.067). 相似文献
899.
Weixiao Cao Zhiyong Meng Tao Yie Donghui Zhang Boxuan Yang 《Journal of polymer science. Part A, Polymer chemistry》1999,37(14):2601-2606
The sulfonate-containing polyelectrolytes (SPE) from sulfonation of polystyrene (PS) and copolymerization of 3-sulfo-propyl methacrylate, potassium salt (SPMS) with styrene (S) were prepared. Photosensitive polyelectrolyte complexes (PECDR) derived from SPE and diazoresin (DR), which does not dissolve in water or organic solvent due to its ionic crosslinking structure, dissolves in aqueous solution of sodium dodecyl sulfate (SDS) due to the dissociation of PECDR and the hydrophobic interaction between SDS and the polymer chain. The photosensitive behavior and thermostability of the PECDR were investigated, and it was found that the thermostability of PECDR increases dramatically in SDS aqueous solution. It was proposed that the higher thermostability of PECDR in SDS aqueous solution is due to an aggregation of SDS molecules around the diazonium group of the PECDR, which protects the N group of the DR from attack by the nucleophiles. The image-forming behavior of PECDR by ultraviolet (UV) light was examined and considered to be different from other PECs. It was concluded that the photoimaging behavior of PECDR is based on a reaction in which an ionic bond converts to a covalent bond. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2601–2606, 1999 相似文献
900.
Zuifang Liu Brian W. Brooks 《Journal of polymer science. Part A, Polymer chemistry》1999,37(3):313-324
Redox polymerizations of acrylic acid in inverse dispersion and in aqueous solution (with surfactant) were conducted by using sodium metabisulphite/potassium bromate initiators. The monomer conversions were determined by using high‐performance liquid chromatography, and the polymer particles in the final lattices were examined using a scanning electron microscope with freeze‐fracture equipment. Experimental rate expressions implied that complex reactions are involved in the redox polymerizations. A chemical reaction scheme was proposed, and kinetic models were developed for the redox polymerization in aqueous solution. Comparison between the experimental rate expressions and the kinetic models suggested a combination of bimolecular and monomolecular termination modes, a chain transfer function of the surfactant, and an oxidizing role of the oxygen molecules. The differences in the experimental rate expressions between the redox polymerization in inverse dispersion and that in aqueous solution are in good agreement with the kinetic model predictions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 313–324, 1999 相似文献