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21.
Jerzy Minczewski und Cezary Rózycki 《Fresenius' Journal of Analytical Chemistry》1968,239(3):158-163
Zusammenfassung Eine Methode zur Zinkbestimmung in Eisen(III)-oxid wird vorgeschlagen. Sie beruht auf der Extraktion des Zinkthiocyanatkomplexes aus schwach saurer Lösung mit Isoamylalkohol. Eisen wird mit Ammoniumfluorid, Kupfer mit Natriumthiosulfat maskiert. Kobalt und Nickel stören nicht, wenn der Extrakt mit einer Waschlösung, die Nitroso-R-Salz enthält, gewaschen wird. Zink wird mit einer Pufferlösung (pH 9) re-extrahiert und mit Dithizon colorimetrisch bestimmt. Bei der Extraktion wird Zink gleichzeitig von gröeren Mengen Cd, Pb und Bi, die die colorimetrische Bestimmung in ammoniakalischer Lösung stören, abgetrennt.
Thiocyanate extraction and dithizone determination of zinc in iron(III) oxide
A Separation of microgram amounts of zinc from large amounts of iron (100 mg) and from 100 g of Co, Cd, Ni, Cu and 200 g of Bi, Pb has been worked out. Zinc is extracted by isoamyl alcohol from a solution containing ammonium thiocyanate, ammonium fluoride (for masking iron) and sodium thiosulphate (for masking copper). Cobalt and nickel are removed from the extract by shaking with a washing solution containing nitroso-R-salt. Zinc is in this way also separated from Cd, Pb and Bi interfering with the colorimetric determination with dithizone. The method was applied to the determination of zinc in ferric oxide.相似文献
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The efficient cross-metathesis of vinylsilanes carrying electron-withdrawing substituents with various olefins is described. High yields and selectivities were obtained when styrene, 1-hexene, and selective functional allyl derivatives were used as the olefins. 相似文献
26.
The effect of increase of polarity of the solvent binary mixture methanol-benzene and acetonitrile-chloroform on the selectivity and the rate of metalloene reaction of different allyltin compounds with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), diethyl azodicarboxylate (DEAD) and singlet oxygen was studied. The more polar solvent favored the production of the M-ene product. Analogous comparative studies were carried out in Et2O and 4 mol dm−3 solutions of LiClO4 in diethyl ether. All studied reactions were strongly catalysed by LiClO4. Physicochemical studies were carried out in purpose to explain the catalytic effect of LiClO4 on the aforementioned reactions. In case of singlet oxygen and diethyl azodicarboxylate it was presumably a result of facilitation of the formation of the polar intermediate by the ionic medium. Whereas, in case of PTAD the mentioned previously effect could be associated with lowering its LUMO by association with lithium. The analogous catalytic effect of LiClO4 was also observed for reactions of organotin phenoxides with DEAD and bis(trichloroethyl) azodicarboxylate leading to corresponding ring-aminated phenols in excellent yield, and with diethyl acetylenedicarboxylate giving a mixture of corresponding vinyl ethers and ring ethenylated phenols. Organotin phenoxides were distinctly more active than the corresponding phenols. 相似文献
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1-(Trimethylsilyl)-1-alkenes of general formula CH3(CH2)nCH?CHSi(CH3)3, where n = 3–15, have been prepared by a novel method, viz. by an effective cross-metathesis of vinyltrimethylsilane with 1-alkenes catalyzed by RuCl2(PPh3)3. Excess of 1-alkene in the reaction mixture gave 1-(trimethylsilyl)-1-alkenes in good yields of up to 60% (in terms of vinylsilane). The products were identified by NMR spectroscopic (1H, 13C NMR) and GC MS methods. 相似文献
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Glen P. Junor Jan Lorkowski Dr. Cory M. Weinstein Dr. Rodolphe Jazzar Prof. Dr. Cezary Pietraszuk Prof. Dr. Guy Bertrand 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22212-22217
Selenium NMR has become a standard tool for scaling the π-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene–selenium 77Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale. 相似文献
30.
We investigate the limit sets
{ f-n °gm(x) : n, m ? \mathbbN}\{ f^{-n} \circ g^m(x) : n, m \in \mathbb{N}\} of sequences of iterates of commuting continuous injections f and g defined in an interval. As an application of the main result we present theorems describing the problem of the existence
and uniqueness of solutions of simultaneous Abel inequalities $\varphi(f(x)) \leq \varphi(x) + 1, \varphi(g(x)) \geq \varphi(x) +
s$\varphi(f(x)) \leq \varphi(x) + 1, \varphi(g(x)) \geq \varphi(x) +
s in the dependence on the parameter s. 相似文献