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91.
Khadija Ben Hadj Hassen Kevin Gaubert Michel Vaultier Mathieu Pucheault 《Green Chemistry Letters and Reviews》2014,7(3):243-249
We describe a study of the gallium(III)-catalyzed 1,6-enynes cycloisomerization reaction in both homogeneous and heterogeneous conditions. With GaBr3 in homogeneous conditions, some particularities were observed in terms of selectivity compared to reported GaCl3-catalyzed reactions. The transfer of the reaction in heterogeneous conditions was realized by supporting Ga(III) salts onto montmorillonite. Both systems were compared based on reaction times, conversion, and selectivity and showed complementary activities. 相似文献
92.
The kinetics of the oxidation of the 2-aminomethylpyridineCoII complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H2O)2]2+[k2+k3/[H+]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied. 相似文献
93.
Yang-Ki Park Kihwan Choi Ahmed Yacine Badjah Hadj Ahmed Zeid A. ALOthman Doo Soo Chung 《Journal of chromatography. A》2010,1217(20):3357-3361
Single drop microextraction (SDME) can be in-line coupled with capillary electrophoresis by attaching a drop to the tip of a capillary. With a 2-layer drop comprised of an aqueous basic acceptor phase covered with a thin organic layer, acidic analytes in an aqueous acidic donor phase can be extracted into the organic layer and then back-extracted into the acceptor phase. However, preconcentration of amino acids and peptides by SDME is difficult since their zwitterionic properties prevent them from being partitioned in the middle organic phase. When amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), amino acids without a charged side chain were converted to carboxylic acids. In the acidic donor phase, those NBD-amino acids were predominantly neutral and they were successfully concentrated into the basic acceptor phase. In the meantime, amino acids with a charged side chain after NBD-F derivatization were not concentrated via SDME. With this selective SDME, we were able to extract acidic and neutral amino acids obtaining several hundred-fold enrichments within 5 min at 25 °C, while leaving basic amino acids—Arg, Lys, and His—in the acidic donor phase. Furthermore, detection sensitivity was enhanced by employing laser-induced fluorescence detection. We then applied this technique to the selective concentration of peptides. 相似文献
94.
Romain Lucas Amel Hadj Bouazza Robert Granet Yves Champavier 《Tetrahedron letters》2008,49(6):1004-1007
Synthesis of a triazole-linked 3′-5′ thymidine dimer making use of 1,3-dipolar cycloaddition is described. The azido-precursor was obtained by regioselective chlorination of thymidine, followed by azidation. The second precursor, a propargyl derivative, was obtained by selective 3′-O-alkylation of thymidine. Two ‘click systems’ were compared to obtain the desired dimer. These reactions were performed by microwave irradiation. 相似文献
95.
96.
An efficient method based, on the acid chloride-imine reaction, is reported for the preparation of 1,3-disubstituted β-lactams in good yield and with high selectivity. 相似文献
97.
Reaction of 2-functional alkyl-1,3-diketones with 30% aqueous formaldehyde using aqueous 6-10M potassium carbonate solution as base, afforded a-functional alkyl vinyl ketones in good yields. 相似文献
98.
Med Abdellatif Bensegueni Aouatef Cherouana Lamia Bendjeddou Claude Lecomte Slimane Dahaoui 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(12):o607-o611
In the two title compounds, cytosinium hydrogen sulfate, C4H6N3O+·HSO4−, (I), and cytosinium perchlorate, C4H6N3O+·ClO4−, (II), the asymmetric units comprise a cytosinium cation with hydrogen sulfate and perchlorate anions, respectively. The crystal structures of (I) and (II) are similar; that of (I) is characterized by a three‐dimensional N—H...O, O—H...O and C—H...O hydrogen‐bonded network. In (I) and (II), two‐dimensional layers are formed by N—H...O and C—H...O hydrogen bonds and, in the case of (I), they are linked by O—H...O hydrogen bonds where the anion acts as a donor and the cation as an acceptor. The hydrogen‐bonded sheets in (II) form an angle of 87.1°. 相似文献
99.
Brahim Ayed 《Comptes Rendus Chimie》2012,15(7):603-608
Single crystals of a new phosphate AgCr2(PO4)(P2O7) have been prepared by the flux method and its structural and the infrared spectrum have been investigated. This compound crystallizes in the monoclinic system with the space group C2/c and the parameters are, a = 11.493 (3) Å, b = 8.486 (3) Å, c = 8.791 (2) Å, β = 114.56 (2)°, V = 779.8 (3) Å3and Z = 4. Its structure consists of CrO6 octahedra sharing corners with P2O7 units to form undulating chains extending infinitely along the [110] direction. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the Ag+ ions are located. The infrared spectrum of this compound was interpreted on the basis of P2O74? and PO43? vibrations. The appearance of νsP–O–P in the spectrum suggests a bent P–O–P bridge for the P2O74? ions in the compound, which is in agreement with the X-ray data. The electrical measurements allow us to obtain the activation energy of (1.36 eV) and the conductivity measurements suggest that the charge carriers through the structure are the silver captions. 相似文献
100.
Sana Hadj Amor 《Mathematical Physics, Analysis and Geometry》2012,15(4):331-342
Starting from results already obtained for quasi-periodic co-cycles in $SL(2, \mathbb R),$ we show that the rotation number of the one-dimensional time-continuous Schr?dinger equation with Diophantine frequencies and a small analytic potential has the behavior of a $\frac{1}{2}-$ H?lder function. We give also a sub-exponential estimate of the length of the gaps which depends on its label given by the gap-labeling theorem. 相似文献