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1.
Mn2O3/-Al2O3 catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn2O3 on the surface of -Al2O3 was determined to be 13.08% from the decomposition mass loss of supported Mn(NO3)2 in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn2O3 on the surface of -Al2O3.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

2.
2-Aryl-3H-indol-3-ones (3a-o) have been synthesized via methanol trapping reaction in singlet oxygenation of 2-arylindoles (1a-o), followed by thermal decomposition of the resultant 2-aryl-2-methoxy-3-oxo-2,3-dihydroindoles (2a-o) in good yields.  相似文献   

3.
The oxidative dehydrogenation (ODH) of isobutane over Cr2O3/La2(CO3)3 has been investi- gated in a low-pressure Knudsen cell reactor, under conditions where the kinetics of the primary reaction steps can be accurately determined. By heating the catalyst at a constant rate from 150-300oC, temper- ature uctuations due to non-equilibrium adsorption are minimized. The evolved gas profiles show that ODH to isobutene and water is a primary reaction pathway, while carbon dioxide, which forms from the catalyst during reaction, is the only other product. This CO2 evolution may enhance the activity of the catalyst. Isobutene formation proceeds with the participation of lattice oxygen from the Cr2O3/La2(CO3)3 catalyst. The small pre-exponential factor is expected for a concerted mechanism and for such a catalyst with a small surface area and limited porosity.  相似文献   

4.
Thedevelopmentofnewandeffcientsyntheticmethodologiesfortheselectiveintroductionoffluorine-c0ntaininggroupintoorganicmoleculesiscurrentlyofconsiderableinterestbecauseoftheiruniquebiologicalactivitiesinmedicineandagrochemicals.lThoughsomereportsonthesynthesisoffluoroalkylsubstitutedpyrazolesappearedinrecentyears2-synthesisof4-fluoroalkylsubstitutedpyrazolesisquitelimited3.Inacontinuousstudyonthesynthesisoffluorine-containingheterocycles,wefoundethyl3-fluoroalkyl-3-hal0acrylate4couldreactwithCH2…  相似文献   

5.
To study the role of H-bonds in stabilizing β-peptidic secondary structures, we have synthesized β-oligopeptides (up to the octadecamer 12 ) consisting of β2- and β3-homoproline, i.e., β-peptides lacking amide protons. The enantiomer purity of the building block β2-homoproline (nipecotic acid, 4 ) was determined by HPLC analysis of the N-(2,4-dinitrophenyl) derivative 5 on a Chiralcel-OD column (cf. Fig. 2). The CD spectra of the all-(S)-β2- and all-(S)-β3-HPro-containing β-peptides display novel and intensive CD patterns which may be indicative of a secondary structure (cf. Fig. 3). It is noteworthy that a distinct CD pattern was observed with the β3-HPro derivatives containing as few as three residues ( 7a ). The crystal structure of a N-deprotected β3-HPro-tripeptide 7c is presented (cf. Figs. 4 and 5), and a model for the structure of β-peptides consisting of β3-HPro is discussed (cf. Figs. 6 and 7).  相似文献   

6.
The oxidative dehydrogenation (ODH) of isobutane over Cr2O3/La2(CO3)3 has been investigated in a low-pressure Knudsen cell reactor, under conditions where the kinetics of the primary reaction steps can be accurately determined. By heating the catalyst at a constant rate from 150-300℃, temperature fluctuations due to non-equilibrium adsorption are minimized. The evolved gas profiles show that ODH to isobutene and water is a primary reaction pathway, while carbon dioxide, which forms from the catalyst during reaction, is the only other product. This CO2 evolution may enhance the activity of the catalyst. Isobutene formation proceeds with the participation of lattice oxygen from the Cr2O3/La2(CO3)3 catalyst. The intrinsic Arrhenius rate constant for the ODH of isobutane isk(s-1) = 1011.5±2.2exp{-((55±5) -ΔHads kJmol-1)/RT}The small pre-exponential factor is expected for a concerted mechanism and for such a catalyst with a small surface area and limited porosity.  相似文献   

7.
Effect of surface spins in chromium oxide (Cr2O3) coated maghemite (γ-Fe2O3) nanoparticles (13 nm) as prepared by microwave plasma technique have been studied in detail. The temperature dependent zero field cooled/field cooled (ZFC/FC) measurements revealed the blocking temperature at TB = 75 K. Simulated ZFC/FC curves exhibited large value of effective anisotropy of Cr2O3 coated γ-Fe2O3 nanoparticles as compared to bulk γ-Fe2O3 but less than bare γ-Fe2O3 nanoparticles. Bloch's law was fitted on MS-T data and revealed the values of Bloch's constant B = 3.523 × 10−4 K−b and Bloch's exponent b = 1.10. The higher value of B than in bulk is due to weaker exchange coupling J (B ̴ 1/J) on the surface of nanoparticle due to disorder surface spins, while lower value of b is due to no spin wave excitation in presence of large energy band gap at nanoscale. Kneller's law fit on HC-T data deviated in all temperature range which is due to strong surface anisotropy, core-shell interactions and superparamagnetism. Interparticle interactions and spin glass behavior were investigated by using different physical laws for f-dependent ac susceptibility and they confirmed the presence of spin glass behavior which is due to disordered frozen surface spins and random interparticle interactions.  相似文献   

8.
The quasi-binary section mullite-zirconium dioxide in the ternary system Al2O3-SiO2-ZrO2, described by an eutectic phase diagram with T e u t = 1750°C, was studied experimentally.  相似文献   

9.
Summary Reaction of 3-azido-5-O-tert-butyldiphenylsilyl-2,3-dideoxy-D-erythro-pentofuranoside (5) with silylated 2-thiouracil and 5-alkoxy-2-thiouracils in the presence of trimethylsilyl trifluoromethanesulfonate afforded an anomeric mixture of the corresponding 3-azido-2,3-dideoxy-2-thiouridine derivatives with the -anomer as the main product. Deprotected nucleosides were obtained by treatment with tetrabutylammonium fluoride.
Ein neuer Weg zur Synthese von 2-Thiouracil-Analogen von 3-Azido-2,3-dideoxy-Nucleosiden
Zusammenfassung Die Reaktion von 3-Azido-5-O-tert-butyldiphenylsilyl-2,3-dideoxy-D-erythro-pentofuranosid (5) mit silyliertem 2-Thiouracil und 5-Alkoxy-2-thiouracil in Gegenwart von Trimethylsilyltrifluormethansulfonat ergab eine anomere Mischung der entsprechenden 3-Azido-2,3-dideoxy-2-thiouridin-Derivate, wobei das -Anomer das Hauptprodukt darstellte. Die ungeschützten Nucleoside wurden mittels Behandlung mit Tetrabutylammoniumfluorid erhalten.
  相似文献   

10.
Summary 2-O-Ethyluracil and 2-O-ethylthymine were silylated with 1,1,1,3,3,3-hexamethyldisilazane and condensed in the presence ofTMS triflate with 2,3-dideoxy-3-fluoro-D-erythro-pentofuranoside, 3-azido-2,3-dideoxy-D-erythro-pentofuranoside, and 2,3-dideoxy-3-phthalimido--D-erythro-pentofuranose derivatives to give the corresponding 2-O-ethyl nucleosides. Deprotection with saturated methanolic ammonia afforded the 2,3-dideoxy-3-fluoro-2-O-ethyluridines, whereas 3-azido-2,3-dideoxy-3-O-ethyluridine was obtained by deprotection with tetrabutylammonium fluoride in tetrahydrofuran. 3-Amino-2,3-dideoxy-3-O-ethyluridine could be obtained only by treatment of the corresponding 3-azido nucleoside with triphenylphosphine in pyridine. 3-Deoxy-2-O-ethyl-3-fluorothymidine (6b) showed moderate activity against HIV-1.
Synthese von 2-O-Ethyl-Analogen von 3-Azido- und 3-Fluor-23-dideoxyuridinen und Bestimmung ihrer biologischen Aktivität gegenüber HIV
Zusammenfassung 2-O-Ethyluracil und 2-O-Ethylthymin wurden mit 1,1,1,3,3,3-Hexamethyldisilazan silyliert und in Gegenwart vonTMS-triflat mit 2,3-Dideoxy-3-fluoro-D-erythro-pentofuranosid, 3-Azido-2,3-dideoxy-D-erythro-pentofuranosid und 2,3-Dideoxy-3-phthalimido--D-erythro-pentofuranosederivaten zu den entsprechenden 2-O-Ethyl-Nucleosiden umgesetzt. Entfernung der Schutzgruppe mit gesättigter methanolischer Ammoniaklösung lieferte 2,3-Dideoxy-3-fluor-2-O-ethyluridin; 3-Azido-2,3-dideoxy-3-O-ethyl-uridin wurde durch Entschützung mit Tetrabutylammoniumfluorid in Tetrahydrofuran erhalten. 3-Amino-2,3-dideoxy-3-O-ethyl-uridin konnte nur durch Behandeln des entsprechenden 3-Azido-Nucleosids mit Triphenylphosphin in Pyridin hergestellt werden. 3-Deoxy-2-O-ethyl-3-fluor-thymidin (6b) zeigt geringe Aktivität gegenüber HIV-1.
  相似文献   

11.
Various pretreatements on those catalysts (oxide form) followed by H2 reduction show that the primary effect of H2 is a dehydration reaction. At high Mo loading, Two consecutive steps of reduction are evidenced: (i) formation of Mo (V) species as Mo(V)OH and (ii) formation of Mo(IV) species characterized by a
(X =V, IV) bridge whose stretching mode is about 760 cm−1. Low Mo loading samples are more difficult to reduce. By comparison with the Mo catalysts, the Wo3γAl2O3 samples are less easily reducible but a similar initial reduced state has been found.  相似文献   

12.
The spectral characteristics and photochemical transformations of adamantane-2-spiro-3-diazirine and its 5-hydroxy derivative were studied. The transformations of the photoexcited molecules of adamantane-2-spiro-3-diazirine in individual solvents and their mixtures and with various sources of UV radiation were studied by gas-liquid chromatography. The main process in saturated hydrocarbons is the formation of diazoadamantane, which is then converted into adamantanone azine. The addition of small amounts of formic or acetic acid leads to the formation of significant amounts of alkyladamantanes, which are the products from transformations of the intermediately formed carbene adamantylidene. Concurrent transformation paths are also observed in cyclohexene. It is suggested that the adamantylidene is preceded by the formation of an exciplex of diazirine with the polar solvent molecule. The ambiphilic nature of adamantylidene in the photolysis of diazirines was demonstrated by concurrent carbenylation.Kiev Polytechnical Institute, L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Higher Chemical Technology School, Prague. Translated from Teoreticheskaya i Ésperimental'naya Khimiya, Vol. 27, No. 2, pp. 211–220, March–April, 1991. Original article submitted July 11, 1989.  相似文献   

13.
Syntheses of novel 3-ethynyl (8), 3-vinyl (10) and 3-acetoxy (13)-2′-deoxy-3-deazauridine analogs starting from the protected 2′-deoxy-3-deazauridine derivative 4 are described.  相似文献   

14.
IntroductionWO3has received considerable attention becauseof its photochromic and electrochromic properties[1—10].Since the photochromic process of WO3can be com-pletely reversible by exposing it to oxygen,it has beenconsidered to be one of the most prom…  相似文献   

15.
High rotational levels of the 001 (Σ(u)) state of BeD(2) are perturbed by the nearby 03(3)0 (Φ(u)) state. Deperturbation analysis results in an experimental value for the vibrational energy of the 030 level.  相似文献   

16.
17.
1 INTRODUCTION Recently, the researches on inorganic-organic hy-brid compounds represent an advanced field in mate-rial science[1]. At the molecular level, the combina-tion of two extremely different components providesan avenue to design new hybrid materials as well asthe ability to modulate properties of one or more ofthe components[2~6]. Some attractive properties, suchas efficient luminescence[2~4], ideal thermal and me-chanical stability, interesting magnetic[5], non-linearoptical[…  相似文献   

18.
2′,3′-Dideoxy-2′-fluorokanamycin A (23) was prepared by condensation of 6-azido-4-0-benzoyl-2,3,6-trideoxy-2-fluoro-α-D-ribo-hexopyranosyl bromide (13) and a protected disaccharide (19). Methyl 4,6-0-benzylidene-3-deoxy-β-D-arabino-hexopyranoside (5) prepared from methyl 4,6-0-benzylidene-3-chloro-3-deoxy-β-D-allo-hexopyranoside (1) by oxidation with pyridinium chlorochromate followed by reduction with Na2 S2O4 was fluorinated with the DAST reagent to give methyl 4,6-O-benzylidene-2,3-dideoxy-2-fluoro-β-D-ribo-hexopyranoside (7). Successive treatment of 7 with NBS, NaN3 and SOBr2 gave 13. The structure of the final product (23) was determined by the 1H and 19F and shift-correlated 2D NMR spectra.  相似文献   

19.
The selective catalytic reduction of nitrogen oxides by hydrocarbons (HC-SCR) has attracted much attention as an efficient way to remove NO in the presence of excess oxygen1-2. The metal oxides are the most promising catalysts for the SCR of NO because of their high activity and selectivity3-5. In the previous work, the metal oxides such as Ag, Sn, In, Co supported on alumina for NO reduction were investigated6-8, however, the HC-SCR is usually suppressed in the presence of H2O and S…  相似文献   

20.
L-Nucleosides have attracted considerable attention since many analogs have exhibited a higher antiviral potency and selectivity than their corresponding D-isomers1. In particular, (-)-(2R, 5S)-1-[(2-hydroxymethyl)-oxathiolan-5-yl]cytosine (3TC, Lamivu- dine)2,its 5-fluoro analog [(-)-FTC, Coviracil]3 and (-)--L-2',3'-dideoxy-5-fluorocytidine (L-FddC)4 are in various stages of preclinical or clinical trials as anti-HIV and anti-HBV agents. Furthermore, the introduction of a 2'--fluo…  相似文献   

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