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71.
The amidinoethylation of alcohols takes place by the addition of sodium alkoxides 2 (R1 = Me, Et) to the CC double bond of a variety of N,N'-substituted-propenamidines 1 (Method A). This illustrates the activation of the CC double bond by the conjugated amidine function and provides a new class of Michael acceptors for alcohols. However, this activation is poorer than with other nucleophiles or Michael acceptors. The amidinoethylation makes available 3-alkoxy-N,N'-substituted-amidines not easily accessible by other classical methods. However, it is demonstrated that the general N,N'-substituted-amidine synthesis via the nitrilium salts can also apply to nitrile compounds having an alkoxygroup present on the molecule (method B). Since the cyanoethylation of alcohols (4) is a very fast and facile reaction the method B is the preferred strategy for the synthesis of 3-alkoxy-N,N'-substituted-propanamidines 3. 相似文献
72.
Rudolf Wagner 《Fresenius' Journal of Analytical Chemistry》1976,282(4):315-321
Summary Problems, techniques and means of water sampling are reviewed. Applicability and performance are discussed with regard to individual and composite samples, and also to automatic sampling. Storage and preservation of samples are dealt with.
Probenahme und Behandlung von ProbenWasser
Zusammenfassung Probleme, Verfahren und Hilfsmittel bei der Probenahme von Wasser werden behandelt. Ausführung und Anwendbarkeit von Einzel und Mischproben sowie der automatischen Probenahme werden diskutiert, ebenso die Aufbewahrung und Konservierung von Proben.
Start of discussion held at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria. 相似文献
73.
74.
Andreas Hofer Eva Brosche und Rudolf Heidinger 《Fresenius' Journal of Analytical Chemistry》1971,253(2):117-119
Zusammenfassung Eine rasche und selektive Methode zur Bestimmung von wasserlöslichem Bor in Mischdüngern wird beschrieben. Bor wird aus der Probelösung, die etwa 0,1 N an Salzsäure sein soll, durch zweimaliges Schütteln mit 20%iger Lösung von 2-Äthyl-1,3-hexandiol in Methylisobutylketon isoliert. Anschließend wird es mit 0,5 N Natronlauge in die wäßrige Phase zurückgeschüttelt und mit, Azomethin H spektralphotometrisch bei 415 nm bestimmt.
Der Direktion der Österreichischen Stickstoffwerke A.G. danken wir für die Erlaubnis zur Veröffentlichung. 相似文献
Spectrophotometric determination of water-soluble boron in complex fertilizers using azomethine h following a separation by extraction with 2-ethyl-1,3-hexanediol
A rapid and selective method for the determination of water-soluble boron in complex fertilizers is described. Boron is separated from the sample solution, which should be approximately 0.1 N in hydrochloric acid, by shaking twice with 20% solution of 2-ethyl-1,3-hexanediol in hexone. Following this extraction boron is back-extracted into the aqueous phase with 0.5 N sodium hydroxide. It is finally determined spectrophotometrically at 415 nm using azomethine H as reagent.
Der Direktion der Österreichischen Stickstoffwerke A.G. danken wir für die Erlaubnis zur Veröffentlichung. 相似文献
75.
Marc Henry 《Journal of Cluster Science》2003,14(3):267-287
Among Achim Müller's prolific crystal structure database, we have selected two crystalline phases in order to perform a whole and complete characterization of water structure at the nanometer scale. The first chosen example involves the Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24] 76H2O compound synthesized and characterized in 1994. Some very interesting yet unnoticed water clusters may be evidenced in the voids generated by the stacking of the polyanionic units. Among them, we have been able to characterized a pure water crown (H2O)18, a loose association of three strongly solvated ammonium ions [H3N–HOH2]+ mediated by two water dimers and one water molecule, a perfectly planar alternating six-member ring [(NH4)3(H2O)3]3+, a puckered chair-shaped hexagonal ring [(NH4)2(H2O)4]3+ and two triangular pyramidal water tetramers (H2O)4. It was also shown that the crown and the chair ring was involved through further hydrogen bonding into the formation of a quite novel supramolecular layer modeling the structure of water in contact with a polyelectrolyte. The second example involves the (gua)32[Mo132O372(H2O)72(SO4)10(H2PO2)20(gua)20]nH2O compound synthesized and characterized in 2002. Here, we provide for the first time a complete structural analysis of all the various hydrogen bond patterns encountered in this system. Among them we may cite, an intramolecular web covering the internal cavity, an intramolecular finite system involving the guanidinium cations and the nine-member ring pores of the Mo132 shell and a central pure water cluster of one hundred water molecules. In this last case, the evolution of the hydrogen bond strengths on a per H-bond basis or within supramolecular aggregates ([H2O]20, [H2O]40, and [H2O]100) is quantitatively studied from standpoints involving both geometry (H–OO bond angles distribution) and energy (partition functions). A survey of other crystalline phases involving water clusters is also presented. It is hoped that the study of these new clusters in a very next future will allow us to solve the well-known water puzzling behaviors. 相似文献
76.
Evelina Liarou Yisong Han Ana M. Sanchez Marc Walker David M. Haddleton 《Chemical science》2020,11(20):5257
Rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. The disproportionation of Cu(i)/Me6Tren in water towards Cu(ii) and highly reactive Cu(0) leads to O2-free reaction environments within the first seconds of the reaction, even when the reaction takes place in the open-air. By leveraging this significantly fast O2-reducing activity of the disproportionation reaction, a range of well-defined water-soluble polymers with narrow dispersity are attained in a few minutes or less. This methodology provides the ability to prepare block copolymers via sequential monomer addition with little evidence for chain termination over the lifetime of the polymerization and allows for the synthesis of star-shaped polymers with the use of multi-functional initiators. The mechanism of self-deoxygenation is elucidated with the use of various characterization tools, and the species that participate in the rapid oxygen consumption is identified and discussed in detail.The rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. 相似文献
77.
Marc Wende 《Journal of fluorine chemistry》2003,124(1):45-54
Most compounds designed for immobilization in fluorous media feature linear pony tails of the formula (CH2)m(CF2)n−1CF3 [(CH2)mRfn]. This paper presents a first-generation approach to compounds with branched or “split” pony tails of the formula (CH2)lCH[(CH2)mRfn]2. Allyl tri(n-butyl)tin is reacted twice with perfluorooctyl iodide (Rf8I; first, photochemical, 78-81%; second, thermal with radical initiator, 71%; 13-18 g scales) to give the secondary alkyl iodide ICH(CH2Rf8)2 (3). A subsequent Ni(Cl)2(PPh3)2-catalyzed reaction with allyl tri(n-butyl)tin yields the branched alkene H2CCHCH2CH(CH2Rf8)2 (74%). A palladium-catalyzed Heck coupling with OP(p-C6H4Br)3 gives the fluorous phosphine oxide OP(p-C6H4CHCHCH2CH(CH2Rf8)2)3 (84%), and Pd/C-catalyzed hydrogenation affords OP(p-C6H4(CH2)3CH(CH2Rf8)2)3 (>99%). Reduction with SiHCl3 gives P(p-C6H4(CH2)3CH(CH2Rf8)2)3, which is protected as the air-stable borane adduct H3B·P(p-C6H4(CH2)3CH(CH2Rf8)2)3 (9, 64%). The CF3C6F11/toluene partition coefficient of 9 is much higher than that of the analog with p-(CH2)3Rf8 groups (96.6:3.4 versus 37.3:62.7). The iodide 3 is unreactive towards PAr3 at 175-250 °C. However, a CuBr-catalyzed reaction with C6H5MgBr gives C6H5CH(CH2Rf8)2, which also exhibits a high partition coefficient (97.9:2.1). 相似文献
78.
Oxidation reactions of an anionic gallium(I) N-heterocyclic carbene analogue with group 16 compounds
The reactivity of an anionic gallium(I) heterocycle, [K(tmeda)][:Ga([N(Ar)C(H)]2)], Ar = C6H3Pr(i)2-2,6, towards sources of elemental chalcogens and diorgano-dichalcogenides has been investigated and comparisons drawn with the reactivity of the valence isoelectronic N-heterocyclic carbene class of ligand. The reactions of the heterocycle with N2O or (Te)PEt3 yielded the dimeric, dianionic gallium(III) complexes, [K(L)]2[(mu-E)Ga([N(Ar)C(H)]2)]2, E = O, L = tmeda; E = Te, L = THF. Treatment of [K(tmeda)][:Ga([N(Ar)C(H)]2)] with the diphenyl dichalcogenides, PhEEPh, E = Se or Te, gave the one dimensional polymer, [K[(PhSe)2Ga([N(Ar)C(H)]2)]]infinity and the monomeric complex, [K(OEt2)3][(PhTe)2Ga([N(Ar)C(H)]2)], respectively. The X-ray crystal structures of the four complexes are reported. 相似文献
79.
A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO3. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml−1 for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications. 相似文献
80.
A method for the quantification of clindamycin in animal plasma using high-performance liquid chromatography combined with electrospray ionization mass spectrometry (LC/ESI-MS/MS) is presented. Lincomycin is used as the internal standard. The sample preparation includes a simple deproteinization step with trichloroacetic acid. Chromatographic separation is achieved on an RP-18 Hypersil column using gradient elution with 0.01 M ammonium acetate and acetonitrile as mobile phase. Good linearity was observed in the range 0-10 microg ml(-1). The limit of quantification of the method is 50 ng ml(-1) and the limit of detection is 1.3 ng ml(-1). The method was shown out to be of use for pharmacokinetic studies of clindamycin formulations in dogs. 相似文献