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101.
Ovakimyan M. Zh. Barsegyan S. K. Karapetyan A. A. Panosyan G. A. Indzhikyan M. G. 《Russian Chemical Bulletin》2002,51(9):1744-1747
The reactions of phenylhydrazine and hydroxylamine with (-X-ethyl)triphenylphosphonium salts (X = Ph, Ph3P+Br–) (1, 2) afforded the corresponding -N-ethyl-substituted triphenylphosphonium salts (3, 4). The reaction of triphenyl(2-phenylhydrazinoethyl)phosphonium bromide 3with an aqueous solution of NaOH in benzene afforded a statistical mixture of the nisand transisomers of 2-(diphenylphosphoryl)acetaldehyde phenylhydrazone. (2-Hydroxyaminoethyl)triphenylphosphonium bromide reacted with sodium methoxide to give O-phosphobetaine. 相似文献
102.
Xirong Huang Nianqin Jie Shuhua Han Wenjuan Zhang Jianping Huang 《Mikrochimica acta》1997,126(3-4):329-333
The coordination reactions of bromopyrogallol red (BPR) with tri- and hexavalent chromium in the presence of cetyltrimethylammonium bromide (CTAB) have been studied by absorption spectrometry. Results show that the reactions of Cr(VI) and Cr(III) with BPR in the absence or presence of CTAB have different temperature dependences. The reaction mechanism of Cr(VI) is that Cr(VI) is first reduced by BPR to Cr(III) and then the Cr(III) produced reacts with BPR. Based on the study on the coordination reactions and the effects of surfactants upon them, a simple, rapid, sensitive and accurate method for Cr speciation has been developed. Over the range of 0–8 g Cr(VI) or 0–12g Cr(III) per 25ml final volume, the calibration curve is linear with a detection limit of 3.5 × 10–7 mol/1 for Cr(VI) or 4.4 × 10–7 mol/1 for Cr(III). 相似文献
103.
The elution of ions from a C18 column with mobile phases containing methanol (60%, v/v) and aqueous buffers is studied by mass spectrometry. It is demonstrated that the anions are excluded from the stationary phase by the ionized silanols. However, the ionized silanols interact strongly with cations, which are retained in the column. These cations are later eluted from the column by ion exchange with the cations present in the pH buffered mobile phase. The size of the ions, the mobile phase cation concentration and the mobile phase pH are the main parameters that affect elution of the retained cations. It is also demonstrated that there are at least two different types of ionizable silanols, with different acidities, that contribute to the retention of cations. An estimate of the pKa values of these two groups of silanols in 60% methanol is given. 相似文献
104.
Denilson S.S. dos Santos Alete P. Teixeira José T.P. Barbosa Sérgio L.C. Ferreira Maria das Graças A. Korn Leonardo S.G. Teixeira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In this work, the use of cetyltrimethylammonium bromide as surfactant for the preparation of oil-in-water emulsions for the determination of Cu and Cr in gasoline by electrothermal atomic absorption spectrometry (ET AAS) was evaluated. The surfactant amount was tested in the range of 25 to 300 mg, added to 2 ml of gasoline, and completed to 10 mL with 0.1% (v/v) nitric acid solution. 150 mg of surfactant was found optimum, and a sonication time of 10 min sufficient to form an oil-in-water emulsion that was stable for several hours. The ET AAS temperature program was established based on pyrolysis and atomization curves. The pyrolysis temperatures were set at 700 and 1300 °C for Cu and Cr, respectively and the selected atomization temperatures were 2400 and 2500 °C. The time and temperature of the drying stage and the atomization time were experimentally tested to provide optimum conditions. The limits of detection were found to be 5 μg L− 1 and 1.5 μg L− 1 for Cu and Cr, respectively in the original gasoline samples. The relative standard deviation (RSD) ranged from 4 to 9% in oil-in-water emulsions spiked with 5 μg L− 1 and 15 μg L− 1 of each metal, respectively. Recoveries varied from 90 to 98%. The accuracy of the proposed method was tested by an alternate procedure using complete evaporation of the gasoline sample. The method was adequate for the determination of Cu and Cr in gasoline samples collected from different gas stations in Salvador, BA, Brazil. 相似文献
105.
《Arabian Journal of Chemistry》2020,13(1):1198-1228
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds. 相似文献
106.
K. Rosi ReddyCh. Venkateshwar Reddy M. MaheshP.V.K. Raju V.V. Narayana Reddy 《Tetrahedron letters》2003,44(44):8173-8175
N-Butyl-N,N-dimethyl-α-phenylethylammonium bromide catalyzes efficiently the three component condensation reaction of an aromatic aldehyde, a β-keto ester and urea/thiourea under solvent free conditions at 100°C to afford the corresponding dihydropyrimidinone in high yield. 相似文献
107.
L. M. Pisarenko T. V. Maksimova Z. S. Kartasheva O. T. Kasaikina 《Russian Chemical Bulletin》2003,52(7):1500-1503
The temperature effect on the rate of the decomposition of hydroperoxides and the rate of the formation of free radicals in the oxidation of ethylbenzene with molecular oxygen in the presence of -phenylethyl hydroperoxide—cetyltrimethylammonium bromide (CTAB) as a catalytic system for free radical generation was studied by kinetic methods (from the oxygen consumption and hydroperoxide decomposition rates) and the inhibition method involving different acceptors of free radicals. 相似文献
108.
T. M. Ugurchieva A. V. Lozanova M. V. Zlokazov V. V. Veselovsky 《Russian Chemical Bulletin》2007,56(8):1544-1549
trans-Stereoselective electrophilic cyclization of (2R*,SS*)-N, N-diisopropyl-2-phenylsulfinylpent-4-enamide under the action of bromine afforded (3R*,5S*, SS*)-N-(5-bromomethyl-3-phenylsulfinyltetrahydrofuran-2-ylidene)-N,N-diisopropylammonium bromide. Its transformations under the conditions of hydrolysis, dehydrobromination, and hydride reduction
were studied.
Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1485–1490, August, 2007. 相似文献
109.
The method for the synthesis of 4-aryl-2,6,6-trimethyl-5-oxo-5,6-dihydro-4H-thieno[3,2-b]pyrroles from accessible 4-aminothiophene derivatives was developed. 相似文献
110.
The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems. 相似文献