共查询到20条相似文献,搜索用时 15 毫秒
1.
Raymond Gerdil 《Helvetica chimica acta》1970,53(8):2097-2099
The polarographic behaviour of ditosyloxy alkanes TsO(CH2)nOTs in aprotic medium suggests that intramolecular cyclisation takes place after reductive cleavage of a single SO2? O bond at the dropping electrode. This hypothesis was verified by controlled potential electrolysis of the lower homologues at a mercury cathode. High yields of epoxy compounds are obtained by this method. 相似文献
2.
Marie-Christine Almasio Franoise Arnaud-Neu Marie-Jos Schwing-Weill 《Helvetica chimica acta》1983,66(4):1296-1306
Macrocyclic Complexes of Lanthanides: Stability and Electrochemical Behaviour in Methanol and Propylene Carbonate The stabilities of the 1:1 complexes of the trivalent lanthanides with the diazapolyoxamacrocycles (2.1.) and (2.2.1.) in anhydrous methanol and propylene carbonate have been determined at 25°, by competitive potentiometric methods using H+ or Ag+ as auxiliary cations, with Et4NClO4 as supporting-electrolyte. Additional data are also reported for the crown ethers 15C5 and 18C6 in propylene carbonate. It is shown that the diazapolyoxamacrocycles are much stronger complexing agents for trivalent lanthanides than macrocyclic polyethers, and that the bicyclic (2.2.1.) cryptates are more stable than the monocyclic (2.1.) complexes. With increasing atomic number of the lanthanides, the stability increases with diazapolyoxamacrocycles and decreases with cyclic polyethers. The electrochemical reduction of the trivalent samarium and europium cryptates has been investigated by polarography on a dropping Hg-electrode, in water and methanol. In both solvating solvents, the +2 oxidation states of the cations are stabilized by complexation. 相似文献
3.
4.
5.
6.
The behaviour of Na+, K+, Rb+ and Cs+ ions on hydrated antimony pentoxide (HAP) has been studied, in various acid media and in ammonium hydroxide. The retention capacity of HAP for the alkali metal ions, as well as their retention rate, has been determined in all the media studied. Curves showing the variation of distribution coefficient values with acid or base concentration are presented. 相似文献
7.
Marco G. Simona Lucette R. Balsenc Christian K. Jrgensen 《Helvetica chimica acta》1978,61(6):1984-1989
The preparation, crystalline structure, properties and behaviour of the hafnium bis (monohydrogen phosphate) monohydrate as a cationic exchanger have been studied. The crystalline product has been characterized by elemental analysis, X-ray Powder patterns, thermal analysis, photoelectron spectrometry and infra red spectroscopy. A layered structure in which the hafnium and phosphorus atoms are disposed in such a way as to form zeolitic-type cavities is suggested. The reversibility of the exchange with respect to sodium ions is discussed and can be related to the water content of the exchanger. 相似文献
8.
The partial synthesis of pollinastanol (14) from cycloartanol (3) is reported. The transformation proceeds through the methylenic intermediate 12; the ring enlargement with cyanogen azide affords pollinastanone (13) further reduced to 14, The 4-keto isomer of pollinastanone (17) as well as a series of 5-β isomeric compounds are also described. 相似文献
9.
A comparative study is made of the reproducibilities obtained for the determination of total carbon in uranium monocarbide by different analytical techniques: macro and microgravimetry, electrical conductivity, thermal conductivity, coulometry, gaseous volumetry and manometry. 相似文献
10.
Michel Farnier Michle Brost Bernard Hanquet Roger Guilard 《Journal of heterocyclic chemistry》1986,23(2):517-521
Two convenient preparations of azido-1,2-dithienylethenes are described. The synthesis of azido-1,2-dithienylethanes proceeds via metalation (n-Buli) and subsequent treatment by tosylazide of bromo-1,2-dithienyl-ethanes. The structures of the obtained derivatives were established on the basis of 1H nmr, ir, and mass spectral data. 相似文献
11.
12.
Marie-Florence Grenier-Loustalot 《Journal of polymer science. Part A, Polymer chemistry》1983,21(9):2683-2695
Carbon 13 nuclear magnetic resonance spectra (at 62,89 MHz) were obtained for a series of branched heavy alcanes (12-ethyl tricosane, 11,20-diethyl tricontane, 11,18-diethyl octacosane, 11,17-diethyl heptacosane, 11,16-diethyl hexacosane, 9,12-diethyl heneicosane, 5,7-diethyl docosane, 6,7-diethyl docosane, 2 éthyl-hexyl-12 tricosane), which provide a model set for describing the ethyl branched sequences in ethylene butene copolymers and low-density polyethylene (LDPE). For ethylene-butene copolymers we do not detect any head-to-head polymerization of butene as reported recently (the existence of a 1,2-ethyl pair has not been confirmed by the low-field signal at 41,3 ppm), but only isolated ethyl and 1-3-diethyl branches. The three peaks observed in the methyl region (broad signal) of the spectrum are assigned to butene centered triads, as opposed to branches in positions having different tacticities as reported earlier. Carbon 13 nuclear magnetic resonance spectra of high-pressure polymerized low-density polyethylene have been measured at 62,89 MHz. On the basis of Willbourn's double back biting mechanism, two kinds of complex branches, the 1,3-ethyl pair and 2-ethyl-hexyl, have been assigned. Finally, these results suggest that the ethyl branches in low-density polyethylene are not isolated branches. 相似文献
13.
1,3-Dipolar cycloaddition of two geometrical isomers of nitronic esters to some mono, di and trisubstituted olefines was studied. For each reaction only one orientation of the cycloaddition was observed which is in good agreement with theoretical predictions. The modes of approach of these dipolarophiles by the two nitronic esters were established in most cases. They are discussed in terms of secondary interactions of the frontier orbitals of the reactants. 相似文献
14.
Contribution to the study of the behaviour of catechin in alkaline medium When catechin ( 1 ) is warmed with aqueous alkali it first undergoes rapid epimerisation. After some time a novel bridged carbocyclic enol, catechinic acid ( 3 ) separates out and may be isolated in excellent yield. Eventually catechinic acid isomerises to 2-(3′,4′-dihydroxyphenyl)-3,9-epoxy-6-oxo-bicyclo[3,3,1]-non-7-en-8,9-diol ( 4 ) via an open chain anion ( 5 ) which is also involved in the epimerisation of catechin. Assignments of structure are given and the equilibria observed are discussed. 相似文献
15.
Ethoxycarbonyl group migration in the Wagner-Meerwein rearrangement . 13 β-Hydroxy-esters have been treated with P2O5 in benzene at 80°. Olefin-forming dehydration, when possible, was found to be the main reaction. When this is excluded, tertiary or benzylic hydroxy-esters react in a manner most easily explained by migration of the COOEt group, thus avoiding the formation of α-carbonyl-carbenium ions. On the other hand, in primary hydroxy-esters (incapable of direct olefin formation), phenyl and methyl groups migrate in preference to COOEt, indicating in this case a concerted reaction. 相似文献
16.
Two new xanthone-O-glycoside, the 1,3,5-trihydroxy-xanthone-8-O-β-D -glucopyranoside ( 3 ), the 1,5-dihydroxy-3-methoxyxanthone-8-O-β-D -glucopyranoside ( 4 ), have been isolated from the leaves of Gentiana campestris L . by means of column chromatography on polyamid. Two known xanthones ( 1 , 2 ) which are respectively the aglycones of 3 and 4 and a flavone: iso-orientine ( 5 ) have also been isolated and identified. 相似文献
17.
K. Hayashi A. Droulde F. Kieffer 《Journal of polymer science. Part A, Polymer chemistry》1969,7(1):83-99
The trapping of electrons and styrene cations and anions has been studied in a methylcyclohexane glass by the techniques of deferred luminescence. Radiothermoluminescence curves consist of two peaks, at 90 and 95°K, in this matrix. The second peak increases linearly with styrene concentration up to 2 × 10?2M when it reaches a constant value, whereas the first peak increases from 10?4 to 10?3M and then decreases at higher concentrations and is not discernible at concentrations above 10?2M. We propose two mechanisms which are qualitatively consistent with this behavior and are based essentially on the recombination of styrene cations with thermally detrapped electrons in the first peak and with anions in the second peak. Photothermoluminescence (i.e., thermoluminescence after photoionization with ultraviolet light) similarly consists of the 90 and 95°K peaks for a 10?3M solution and of the 95° peak alone for a 10?d M solution. Radiophotoluminescence excitation spectra at 77°K, corresponding to absorption spectra of trapped electrons and styrene anions, show that anions are the predominant negative species in 10?2 molar solution, and trapped electrons in 10?3 molar solution. Spectral analysis of radiothermoluminescenece shows the presence of two emission bands, one of which is identical with styrene fluorescence excited by the 254 Nm mercury line (λmax = 292, 302, 307, and 317 Nm). The other band has three fairly poorly resolved maxima at 474, 486 and 496 nm and seems to correspond to the fluorescence of C6H5?H-CH3 radicals formed during radiolysis. 相似文献
18.
Electrochemical reduction of Cu2?xS in dimethylsulfoxide in chloride media is described. The material undergoes an electrochemical solution reduction under certain pH and pCl conditions, reduction of the Cu(II) species in the solid leading to destruction of the crystal. The stoichiometry of séveral copper sulfides is measured. 相似文献
19.
Michel Farnier Michle Brost Bernard Hanquet Roger Guilard 《Journal of heterocyclic chemistry》1986,23(2):513-516
Thermal decomposition of azido-1,2-dithienylethenes 1 gave thienyl 4H-thieno[3,2-b]pyrroles 3 . For the 3,4-disubstituted thiophene derivatives 2 , the same reaction led to the amino-1,2-dithienylethenes 4 . In contrast, only azido-1,2-dithienylethanes 7 led to thienyl-5,6-dihydro-4H-thieno[3,4-b]pyrroles 8 . The structure of the obtained derivatives was established on the basis of 1H nmr, ir, and mass spectral data. 相似文献
20.
Synthesis of Methyl Virensate The synthesis of methyl virensate (=methyl 4-formyl-3,8-dihydroxy-1,6,9-trimethyl-11-oxo-11H-dibenzo-[b, e][1,4]dioxepin-7-carboxylate; 18 ) by the condensation of the substituted β-orcinol and orcinol units 9 and 10 followed by formylation and demethylation of the depsidone 13 is described. 相似文献