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151.
Haçan Awad François Trécourt Guy Quéguiner Francis Marsais 《Tetrahedron letters》2004,45(42):7873-7877
4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu3(TMP)MgLi2 in THF at −10 °C, as evidenced by trapping with I2. The use of Bu(TMP)2MgLi in Et2O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I2, the former using 1/3 equiv of Bu2(TMP)MgLi and the latter using 1 equiv of (TMP)3MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation. 相似文献
152.
Phosphate selective electrodes have been produced based upon rubbery membranes containing heterocylic macrocycles as sensors covalently bound to a cross-linked polystyrene-block–polybutadiene-block–polystyrene (SBS) polymer. The membranes were robust and the best HPO42−-selective membrane fabricated was composed of 7.1% (m/m) dicumyl peroxide, 28.3% (m/m) 2-nitrophenyloctylether, 9.8% (m/m) 3-(10-undecenyl)-1,5,8-triazacyclodecane-2,4-dione, 31.0% (m/m) SBS and 23.8% (m/m) PoleStar™ 200R (clay-based filler). The characteristics of this electrode were a linear Nernstian range of 3.9×10−3 to 1×10−6 mol dm−3 HPO42− with a limit of detection of 1.0×10−6 mol dm−3 HPO42−, a slope of −29.7±0.9 mV per activity decade and a pH range from 6 to 8. Selectivity coefficients for phosphate against various interfering anions (chloride, sulfate and nitrate) were determined. Response times were 2 min or under, stability of response and electrode lifetime in continuous use were also very satisfactory. The response behavior of HPO42−-ISEs based upon mobile and bound ionophores was comparable and suggests that mobility of the ionophore is not necessary to obtain a working ISE and that covalent binding of ionophores can be used to produce ISEs of increased stability and robustness. 相似文献
153.
Maria Luisa Moyá Antonio Barrios Maria del Mar Graciani Rafael Jiménez Ernestina Muñoz Francisco Sánchez John Burgess 《Transition Metal Chemistry》1991,16(2):165-168
Summary The kinetics of replacement of 4,4-bipyridine, (4,4-bipy), and 4-cyanopyridine, (4-CNpy), by cyanide in [Fe(CN)5-(4,4-bipy)]3-. at 298 K have been studied in binary aqueous mixtures containing different amounts of t-butanol, methanol, glycerol, ethyleneglycol and sucrose. The plots of logarithms of the limiting rate constantsversus the mole fraction of water are linear over the entire composition range studied, showing the importance of solvation phenomena. A different straight line of log (kL/s–1)versus XH2O is obtained for each mixture, indicating the influence of other solvent parameters on the reaction rate. A multiparameter regression of G
exp
with A (acidity vector), B (basicity vector) and GE is used for both reactions; plots of G
calc
versus G
exp
are linear with slopes of near unity. 相似文献
154.
Vesna Radulovi? Alessia Bacchi Giancarlo Pelizzi Du?an Sladi? Ilija Br?eski Katarina Andjelkovi? 《Monatshefte für Chemie / Chemical Monthly》2006,23(3):681-691
Complexes of Pt(II), Pd(II), and Ni(II) with the condensation derivative of 2-(diphenylphosphino)benzaldehyde and semioxamazide
were synthesized, characterized, and their antimicrobial activity was evaluated. The ligand and the complexes were characterized
by spectroscopic methods with the particular accent on NMR spectral analysis. For the palladium(II) complex, the crystal structure
was determined by X-ray analysis. In all the complexes the ligand is coordinated as a tridentate via a P, N, O donor set. The Pd(II) and Pt(II) complexes have a square planar geometry, whereas the geometry of the Ni(II) complex
is tetrahedral. The ligand showed antibacterial and antifungal activity, which was enhanced upon complexation. 相似文献
155.
A spectrofluorimetric method for the simultaneous determination of dysprosium, europium, gadolinium and terbium in ternary and quaternary mixtures by the use of pyridine-2,6-dicarboxylic acid as a chelating agent was developed. The influence of chemical variables affecting the analytical reaction was evaluated. A partial least-squares procedure and PC Quant software were used to assess data obtained from a variable number of calibration solutions and wavelengths. The ensuing method was validated by applying it to the analysis of synthetic ternary (Eu-Dy-Tb) and quaternary mixtures (Eu-Dy-Gd-Tb) over the concentration ranges 60-550 mug Eu l(-1), 30-400 mug Dy l(-1) and 30-400 mug Tb l(-1) in the former, and 20-220 mug Eu l(-1), 20-235 mug Dy l(-1), 25-230 mug Gd l(-1) and 75-230 mug Tb l(-1) in the latter. The results obtained by using the two quantitation procedures are compared. The relative errors in the determinations were less than 8% in most cases. 相似文献
156.
Alpha-fluorosulfonamides were prepared by electrophilic fluorination of tertiary sulfonamides using N-fluorobenzenesulfonimide as fluorinating agent and utilizing the dimethoxybenzyl group (DMB) as a new sulfonamide protecting group. Removal of the DMB group with TFA/CH(2)Cl(2) gave primary and secondary alpha-fluorosulfonamides. 相似文献
157.
Milena Jelikić-Stankov Dejan Stankov Dušan Malešev Zorica Radović 《Mikrochimica acta》1991,103(1-2):65-70
By means of spectroscopic methods it has been found that demeclocycline reacts with molybdate ions forming a complex compound [MoO3HDMTC]2–. The relative stability constant of this compound has been determined by applying spectrophotometric methods. Under optimum conditions for complex formation a very sensitive spectrophotometric method for the estimation of demeclocycline in the concentration range 5.0–35.1 g/ml is proposed. The detection limit of the method is 2.5 g/ml of demeclocycline. The relative standard deviation (n=10) varies between 0.76% and 1.46%. The method proved to be accurate and sensitive for the analysis of the demeclocycline content in tablets. 相似文献
158.
Hakki İsmail Erdoğan 《Journal of Geometry》1991,40(1-2):47-59
In this paper, the problem of determining the pencils of circles which form a hexagonal n-web in E2, is completely solved. It is well-known that n pencils of circles orthogonal to a fixed circle form a hexagonal n-web. Therefore, the main problem is the determination of all circle pencils which form a hexagonal n-web and which do not cut a fixed circle orthogonally. In this connection the following results have been obtained: The number of hexagonal 4-webs is six, whereas the number of hexagonal 5-webs is two.Finally, after having proved that the number of hexagonal 6-webs is one, it is shown that, for n7, there exist no circle pencils forming a hexagonal n-web without being orthogonal to a fixed circle. 相似文献
159.
光纤松耦合型传感器特性研究 总被引:1,自引:1,他引:0
本文介绍一种实用的光纤传感器,它由二根光纤或多根光纤紧靠一起,并在同一位置除去局部包层,成为松耦合状态,在这种状态下,研究了它的特性和应用。 当耦合间隙中充满某种液体介质时,耦合效率明显增大,因此可以方便地判别该介质是否存在。并且实验证明了一种光纤只能有一种相近于光纤芯子折射率的介质具有最大的灵敏度。当间隙内的介质不变时,耦合功率的大小决定于耦合距离d和耦合长度l,l一旦决定以后,d的调节精度为0.1mm量级,易于在机械结构上实现线性检测。 相似文献
160.
Jim Agler 《Integral Equations and Operator Theory》1982,5(1):608-631
We develop techniques which allow one to describe in simple terms the set of operators on Hilbert space of the form M* () |M, where M is multiplication by z on a Hilbert space of analytic functions satisfying certain technical assumptions, M* () is the direct sum of a countably infinite number of copies of M*, andM is invariant for M* (). One of the main ingredients in our technique is the Arveson Extension Theorem and this paper illustrates the great power and tractability of that theorem in a concrete setting.Research partially supported by NSF grant MCS 81-02518 相似文献