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321.
Marko kof Jurij Svete Branko Stanovnik Ljubo Goli
Simona Goli
-Grdadolnik Lovro Seli
《Helvetica chimica acta》1998,81(12):2332-2340
(5S)-1-Benzoyl-3-[(E)-cyanomethylidene]-5-(methoxycarbonyl)pyrrolidin-2-one ( 5 ) was prepared in four steps from L -pyroglutamic acid ( 1 ). 1,3-Dipolar cycloadditions of diazomethane ( 6 ) and 2,4,6-trimethoxybenzonitrile oxide ( 7 ) gave substituted 1,2,7-triazaspiro[4.4]non-1-en-6-one 12 and 1-oxa-2,7-diazaspiro[4,4]non-1-en-6-one 13 in 38 and 20% de, respectively. On the other hand, reaction of 5 with N-phenylbenzonitrile imines 8 and 9 , generated in situ from the corresponding hydrazonoyl chlorides 10 and 11 , respectively, and Et3N, furnished racemic pyrrolo[3,4-c]pyrazoles 14 and 15 in 61 and 56% de, respectively. Cycloaddition of nitrile oxide 7 , when performed in the presence of Et3N, led to pyrrolo[3,4-d]isoxazole 16 in 85% de. 相似文献
322.
Bohanec Marko Trdin Nejc Kontić Branko 《Central European Journal of Operations Research》2017,25(3):611-625
Central European Journal of Operations Research - A methodological approach to the strategic evaluation of electric energy production technologies in Slovenia is presented. The aim of this work is... 相似文献
323.
324.
Benny Amaechi Stefan Iglauer Christopher H. Pentland Branko Bijeljic Martin J. Blunt 《Transport in Porous Media》2014,103(3):421-436
The trapped saturations of oil and gas are measured as functions of initial oil and gas saturation in water-wet sand packs. Analogue fluids—water, octane and air—are used at ambient conditions. Starting with a sand-pack column which has been saturated with brine, oil (octane) is injected with the column horizontal until irreducible water saturation is reached. The column is then positioned vertically and air is allowed to enter from the top of the column, while oil is allowed to drain under gravity for varying lengths of time. At this point, the column may be sliced and the fluids analyzed by gas chromatography to obtain the initial saturations. Alternatively, brine is injected through the bottom of the vertical column to trap oil and gas, before slicing the columns and measuring the trapped or residual saturations by gas chromatography and mass balance. The experiments show that in three-phase flow, the total trapped saturations of oil and gas are considerably higher than the trapped saturations reported in the literature for two-phase systems. It is found that the residual saturation of oil and gas combined could be as high as 23 %, as opposed to a maximum two-phase residual of only 14 %. For very high initial gas saturations, the residual gas saturation, up to 17 %, was also higher than for two-phase displacement. These observations are explained in terms of the competition between piston-like displacement and snap-off. It is also observed that less oil is always trapped in three-phase flow than in two-phase displacement, and the difference depends on the amount of gas present. For low and intermediate initial gas saturations, the trapped gas saturation rises linearly with initial saturation, followed by a constant residual, as seen in two-phase displacements. However, at very high initial gas saturations, the residual saturation rises again. 相似文献
325.
Through the NMR monitoring of the reactive intermediates in the condensation of barbituric acid with nitrogen containing heterocyclic 2‐carboxaldehydes, a synthetic procedure was developed for the preparation of each of the intermediates. The simple high yield procedure for the preparation of the reductive dimer from corresponding barbituric acid benzylidenes was developed, although we were not able to elucidate the source of the reduction. The structure of the dimer was confirmed by X‐ray analysis. 相似文献
326.
Dominik Cin
i Branko Kaitner 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(4):o226-o229
In the title compounds, 4‐carboxyanilinium bromide, C7H8NO2+·Br−, (I), and 4‐acetylanilinium bromide, C8H10NO+·Br−, (II), each asymmetric unit contains a discrete cation with a protonated amino group and a halide anion. Both crystal structures are characterized by two‐dimensional hydrogen‐bonded networks. The ions in (I) are connected via N—H...Br, N—H...O and O—H...Br hydrogen bonds, with three characteristic graph‐set motifs, viz. C(8), C21(4) and R32(8). The centrosymmetric hydrogen‐bonded R22(8) dimer motif characteristic of carboxylic acids is absent. The ions in (II) are connected via N—H...Br and N—H...O hydrogen bonds, with two characteristic graph‐set motifs, viz. C(8) and R42(8). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in two similar compounds. The presence of the methyl group in (II) at the site corresponding to the hydroxyl group in (I) results in a significantly different hydrogen‐bonding arrangement. 相似文献
327.
328.
Rate constants for the esterification of eleven 2-[(carboxymethyl)sulfanyl]-4-oxo-4-arylbutanoic acids with diphenyldiazomethane in ethanol at 30 °C were determined, and correlated with substituent constants using classical Hammett and related methods. Statistically valid results for the para-substituted compounds were obtained by the Swain–Lupton approach. The compounds studied had significant conformational mobility due to seven rotatable bonds in their backbone. Going beyond the classical Hammett approach, we established a relatively fast procedure to find the optimal conformations that can be used in linear free-energy relationships, combining molecular dynamics with semiempirical calculations, and calculations using a higher level of theory (DFT and MP2). Fair correlations were observed with frontier orbitals, allowing inclusion of ortho-substituted derivatives and clarifying artifact-like data, as perceived by the Hammett-type approach. 相似文献
329.
Preparation of 5-Alkylthio and 5-Arylthiotetrazoles from Thiocyanates Using Phase Transfer Catalysis
A very efficient method of preparation for 5-alkyl and 5-arylthiotetrazoles from the corresponding alkyl or aryl halides is described. The halides are first transformed into thiocyanates which further react with azide, yielding the corresponding tetrazoles with [2+3] polar cycloaddition. All synthetic transformations are performed under phase transfer catalytic conditions. The yields vary from good to excellent except for the preparation of 5-benzylthiotetrazole, where the reaction between benzyl thiocyanate and azide [2+3] cycloaddition is in competition with nucleophilic substitution, with benzyl azide as product. 相似文献
330.
Jelena Milanovic Steva Levic Verica Manojlovic Viktor Nedovic Branko Bugarski 《Chemical Papers》2011,65(2):213-220
Melt dispersion technique was investigated for carnauba wax microparticles production. Microbeads with spherical shape and
narrow size distribution were produced. The main objective of this study was to investigate the effect of significant process
variables (initial wax concentration, stirring speed, stirring time, and surfactants) on sphericity, size distribution, and
morphological properties of wax microparticles. Optimal conditions were evaluated on the basis of particle size distribution
and visual analysis. Surface morphology of microparticles was characterized by scanning electron microscopy (SEM). Effects
of process conditions on the size distribution of particles were evaluated by sieve analysis. Main purpose of these investigations
was to apply optimized parameters to aroma encapsulation for their use in food and feed industry. 相似文献