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971.
A sensitive flotation—spectrophotometric method, based on the ion associate formed by the anionic thiocyanate complex of osmium with the basic dye methylene blue (MB) is described. The ion associate precipitates when the aqueous solution is shaken with toluene, and the separated and washed compound is dissolved in acetone. The molar absorptivity is 2.2 × 105 l mol-1 cm-1 at 655 nm. Beer's law is obeyed. The molar ratio of Os:SCN:MB in the separated and washed ion associate is 1:6:3. Ruthenium reacts similarly. The method is applied to the determination of traces of osmium in crucible platinum after separation of osmium by distillation as tetroxide. 相似文献
972.
A new, fast and simple inorganic chemiluminescence method for the determination of trace amounts of manganese is described. When MnO(-)(4) is injected into 0.40M Na(2)CO(3)-0.70M KOH mixed solution in a reaction cell, the strong chemiluminescence occurs and is recorded. The detection limit is 0.1 ppb Mn and the linear range extends from 0.1 to 10 ppb Mn. A 5-ppb Mn concentration can be determined with a relative standard deviation of 5.6% (15 replicates). The commonly encountered cations do not interfere with the determinations. This method has been successfully applied to the direct determination of manganese in bauxite. The reaction mechanism is also briefly discussed. 相似文献
973.
[reaction: see text] A new nonchain 5-endo radical cyclization starting with xanthates was exploited in a short synthesis of (+/-)-alpha-lycorane and the erythrina ring system. 相似文献
974.
Methyl-5-benzoyl-2-benzimidazole carbamate (mebendazole) is a drug used as an anthelmintic. A high performance liquid chromatography method has been developed in this study to determine mebendazole and its degradation product in the pharmaceutical dosage forms (tablets and suspension). The expected major degradation product of mebendazole in the dosage forms has been prepared, and identified as 2-amino-5-benzoylbenzimidazole. The proposed HPLC assay was found to be selective, accurate (% recoveries were in the range of 99.9-100.9) for both, mebendazole and the degradation product, repeatable and reproducible (replicate measurements for short and long term measurements showed % RSD of =1.4). The methodology could be considered as a stability indicating method for mebendazole in pharmaceutical dosage forms. 相似文献
975.
M.Z. Kassaee S.M. Musavi M. Ghambarian M.R. Khalili Zanjani 《Journal of organometallic chemistry》2006,691(13):2933-2944
For 30 C2GeHX germylenic isomers, one cyclic structure, X-germacyclopropenylidene, and three acyclics are considered, which include: ethynyl-X-germylene, X-vinylidenegermylene, and (X-ethynyl)germylene (X = H, F, Cl, and Br). The global minimum among six isomeric C2GeH2 (where X = H), is found to be cyclic, aromatic, singlet germacyclopropenylidene. In contrast, among the 24 corresponding halogermylenes, C2GeHX (where X = F, Cl, and Br), the global minima switch to acyclic, singlet ethynylhalogermylenes, at eight reasonably high ab initio and DFT levels. The direct resonance interaction between X and the divalent center Ge in the singlet acyclic ethynylhalogermylene structures, is claimed to justify switching of the calculated global minima in the halo derivatives. GIAO-NICS calculations indicate that the X-germacyclopropenylidene isomer is more aromatic for X = H than X = F, Cl, or Br. The angle ∠XGeC bending potential energy curves show the singlet and triplet ethynylgermylene crossing at ≈146°, for X = H. 相似文献
976.
The kinetics of catalytic decomposition of NO over Cu/ZSM-5 catalyst has been studied in an integral flow reactor at atmospheric
pressure. Kinetic analysis is based on the assumption that the surface reaction represents the rate-determining step. On the
basis of theoretical considerations of different interactions between reactants and catalyst, and experimental evidences,
three different mechanistic kinetic models were chosen. Also a power-law model was tested. The best agreement has been achieved
with the model
相似文献
977.
The relative strength of interaction between anionic (SDS) and nonionic surfactant (octaethoxylated oleyl alcohol, GEN) and homologous series of peptides was determined by reversed-phase thin-layer chromatography (RP-TLC) carried out on alumina layers impregnated with paraffin oil. The relative strength of interaction was calculated and was correlated with the physicochemical parameters of peptides. It was established that each peptide interacted with both surfactants and with their mixture (1:1, m/m). The relative strength of interaction depended on the number of amino acid units in the peptide, side chain bulk and electronic properties and hydrophobicity of the amino acids. The impact of individual parameters highly depended on the character of surfactant. The data prove that the retention order of peptides can be modified by adding different surfactants and surfactant mixtures to the mobile phase resulting in improved separation. 相似文献
978.
Summary. Thioamides and thioureas were reacted with tetrabutylammonium periodate at room temperature to afford the corresponding amides and ureas, respectively, under aprotic conditions. 相似文献
979.
R. A. Alieva S. Z. Gamidov F. M. Chyragov A. A Azizov 《Journal of Analytical Chemistry》2005,60(12):1114-1117
A method is developed for cadmium and zinc preconcentration on a minicolumn packed with a new chelating polymer sorbent. The effects of the test solution pH and volume, the sample matrix composition, the eluent volume, and the sample and eluent flow rates are studied. Zinc and cadmium in the eluate are determined by flame atomic absorption spectrometry. Under optimal conditions, the determined ion recovery is more than 95%. The detection limits (3σ, n = 20) are found to be 15.0 (Cd) and 17.2 (Zn) ng/mL. The developed method is employed for cadmium and zinc determination in samples of seawater and water obtained after oil pumping. 相似文献
980.
Protection of various thiols with diphenylmethanol was achieved in high yields at room temperature using catalytic amounts of AlPW12O40 in CH2Cl2. In the presence of this catalyst, protection of SH versus OH was achieved with high chemoselectivity and yields. The catalyst can be easily recovered and reused. Deprotection of DPM thioethers was also achieved using molecular iodine at reflux in CH2Cl2 in high yields. 相似文献