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91.
The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF2O + F2→ CF3OF. The list of catalysts for this process has now been enlarged to include NaF, MgF2, CaF2, SrF2, BaF2 and LaF3. Lithium fluoride and thorium fluoride also give CF3OF but are less active. Perhaps the substances CsF·HF, KAgF4 and NiF2 should be included in this list. Silver fluoride, usually as a mixture of AgF2 with AgF, has been known to catalyze the reaction of CF2O with F2 to give both CF3OF and CF3OOCF3. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF3OOCF3 is very high. It has now been shown that TIF3 behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF3OOCF3 than of CF3OF but require higher temperatures than AgF2 (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed. 相似文献
92.
P. G. Royall D. Q. M. Craig M. Reading T. J. Lever 《Journal of Thermal Analysis and Calorimetry》2000,60(3):795-805
The purpose of this study was to investigate the feasibility of modulating the temperature programme of a conventional DSC
by use of an alternating gas-flow system. Modulated temperature differential scanning calorimetry (MTDSC) is an important
thermal analysis technique but suffers from a limited applicable frequency range due to the mass of the sample and DSC cell
leading to the impingement of thermal conductivity effects. We suggest that the frequency limit can be increased by replacing
the cell as the source of temperature modulation with an external gaseous source, directed towards the sample and reference
pans. In this evaluation, an alternating gas-flow was passed through a line to a forced gas-flow accessory (FGFA). The FGFA
consisted of two matched cylinders containing chambers that allowed pre-temperature-equilibration of the stream of gas before
it was passed over the sample and reference pans. The development of this device revealed the essential practical requirements
of gas-flow modulation for high-frequency temperature modulation. These include the following: an appropriately sealed tunable
gas supply to both sample and reference pans, an effective method for high-frequency cycling of the gas-flow rate, a small
aperture to deliver the flowing gas directly over the pan and a temperature equilibration chamber. The results from samples
of quenched PET and amorphous Saquinavir indicate that gas-flow modulation is indeed feasible, with the FGFA able to raise
the attainable temperature modulation frequency by an order of magnitude compared to conventional MTDSC.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
93.
[structure: see text] [structure: see text] [structure: see text] Several Precipiton phosphines were prepared and employed in the Staudinger reaction and in the reduction of secondary ozonides. Both amines and aldehdyes were obtained in good to excellent yields and purities. After use of the phosphine, isomerization and precipitation of the spent phosphorus reagent were induced by exposure to visible light in the presence of erythrosin B, a triplet sensitizer. Products were isolated by simple filtration. The use of the triplet sensitizer has the added advantage of eliminating [2 + 2] cycloaddition reactions between trans-Precipitons. 相似文献
94.
The [Ru(bipy)(2)(1)](PF(6))(2) (bipy refers to 2,2'-bipyridine) complex, comprising a ruthenium(II) tris(2,2'-bipyridine) luminophore covalently linked to a di[(o-triethyleneglycoxy)phenyl]amine crown ether 1, has been synthesized and fully characterized. The photophysical properties of this metal complex have been examined in solution at ambient temperature. Luminescence from the metal complex is enhanced significantly in the presence of various adventitious cations, including protons. In particular, Li(+) cations bind to the crown ether, as evidenced by (1)H NMR and luminescence spectroscopy. Cation binding serves to decrease the rate of reductive quenching of the triplet state of the metal complex, thereby increasing the extent of luminescence. The solution-phase conformation of [Ru(bipy)(2)(1)](PF(6))(2), with and without encapsulated Li(+), has been examined by 2-D NMR and by molecular dynamics simulations. 相似文献
95.
Jiang J Sarsfield MJ Renshaw JC Livens FR Collison D Charnock JM Helliwell M Eccles H 《Inorganic chemistry》2002,41(10):2799-2806
Eight uranyl compounds containing the dicarboxylate ligands iminodiacetate (IDA) or oxydiacetate (ODA) have been characterized in the solid state. The published polymeric structures for [UO(2)(C(4)H(6)NO(4))(2)] and [UO(2)(C(4)H(4)O(5))](n) have been confirmed, while Ba[UO(2)(C(4)H(5)NO(4))(2)] x 3H(2)O, [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)][UO(2)(C(4)H(4)O(5))(2)] [orthorhombic space group Pnma, a = 10.996(5) A, b = 21.42(1) A, c = 8.700(3) A, Z = 4], and [C(2)H(5)NH(2)(CH(2))(2)NH(2)C(2)H(5)][UO(2)(C(4)H(4)O(5))(2)] [monoclinic space group P2(1)/n, a = 6.857(3) A, b = 9.209(5) A, c = 16.410(7) A, beta = 91.69(3), Z = 2] contain monomeric anions. The distance from the uranium atom to the central heteroatom (O or N) in the ligand varies. Crystallographic study shows that U-heteroatom (O/N) distances fall into two groups, one 2.6-2.7 A in length and one 3.1-3.2 A, the latter implying no bonding interaction. By contrast, EXAFS analysis of bulk samples suggests that either a long U-heteroatom (O/N) distance (2.9 A) or a range of distances may be present. Three possible structural types, two symmetric and one asymmetric, are identified on the basis of these results and on solid-state (13)C NMR spectroscopy. The two ligands in the complex can be 1,4,7-tridentate, giving five-membered rings, or 1,7-bidentate, to form an eight-membered ring. (C(4)H(12)N(2))[(UO(2))(2)(C(4)H(5)NO(4))(2)(OH)(2)] x 8H(2)O [monoclinic space group P2(1)/a, a = 7.955(9) A, b = 24.050(8) A, c = 8.223(6) A, beta = 112.24(6), Z = 2], (C(2)H(10)N(2))[(UO(2))(2)(C(4)H(5)NO(4))(2)(OH)(2)] x 4H(2)O, and (C(6)H(13)N(4))(2)[(UO(2))(2)(C(4)H(4)O(5))(2)(OH)(2)] x 2H(2)O [monoclinic space group C2/m, a = 19.024(9) A, b = 7.462(4) A, c = 2.467(6) A, beta = 107.75(4), Z = 4] have a dimeric structure with two capping tridentate ligands and two mu(2)-hydroxo bridges, giving edge-sharing pentagonal bipyramids. 相似文献
96.
Matthews CJ Elsegood MR Bernardinelli G Clegg W Williams AF 《Dalton transactions (Cambridge, England : 2003)》2004,(3):492-497
The crystal structures of three complexes of dicarboxy-2,2'-bipyridyl ligands, 5,5'-dicarboxy-2,2'-bipyridyl (1) and 4,4'-dicarboxy-2,2'-bipyridyl (2) are reported. [Rh(1H)3] shows two interpenetrating, homochiral rhombohedral networks linked by short carboxylate-carboxylic acid hydrogen bonds, in which each complex acts as a node for six hydrogen bonds. [Ru(1H2)(1H)2] forms only four such hydrogen bonds, leading to the formation of heterochiral chains held together by stacking between bipyridyls. [Co(2H)3] can in principle form six hydrogen bonds, but in practice forms only four in a layer structure where stacking interactions are important. This is attributed to differences in molecular shape. 相似文献
97.
S. M. Matthews A. J. Boegel S. F. Eccles S. G. Homann D. W. Rice J. A. Loftis M. C. Jovanovich R. A. Caufield B. J. Mincher D. H. Meikrantz R. J. Murphy G. L. Gresham M. J. Connoly 《Journal of Radioanalytical and Nuclear Chemistry》1992,161(1):253-264
The Lawrence Livermore National Laboratory (LLNL) and the Idaho National Engineering Laboratory (INEL) are jointly investigating the decomposition of chlorinated hydrocarbons using bremsstrahlung radiation produced by electron accelerators and gamma photons from spent reactor fuel. Experimental results demonstrate an exponential type decay of concentration with dose for volatile organic compounds (VOCs) in ground water and for both polychlorinated biphenyls (PCBs) and insecticides in organic solutions. Experiments were performed at several photon energies and dose rates with various initial concentrations. Mass balance analysis suggests complete mineralization of VOCs in ground water and indicates significant degradation of PCBs and insecticides to VOC type compounds in organic solutions.Work performed under the auspices of the U.S. Department of Energy, DOE Contract Nos. W-7405-ENG-48 and DE-AC07-76IDO1570. 相似文献
98.
The use of chiral secondary amines containing only one branched substituent has been shown to give optimal yields and stereoselectivities in the preparation of α-amino acids using the Petasis reaction. While the use of chiral primary amines generally gives products in low to moderate diastereoselectivity, chiral secondary amines generally give products in >95:5 diastereoselectivity. Additionally, the use of amines with two chiral (and by definition, branched) N-alkyl substituents results in significantly reduced yields with respect to to secondary amines with one or no branched N-alkyl substituents. 相似文献
99.
Harth EM Hecht S Helms B Malmstrom EE Fréchet JM Hawker CJ 《Journal of the American Chemical Society》2002,124(15):3926-3938
The influence of macromolecular architecture on the physical properties of polymeric materials has been studied by comparing poly(benzyl ether) dendrons with their exact linear analogues. The results clearly confirm the anticipation that dendrimers are unique when compared to other architectures. Physical properties, from hydrodynamic volume to crystallinity, were shown to be different, and in a comparative study of core encapsulation in macromolecules of different architecture, energy transduction from the polymer backbone to a porphyrin core was shown to be different for dendrimers as compared to that of isomeric four- or eight-arm star polymers. Fluorescence excitation revealed strong, morphology dependent intramolecular energy transfer in the three macromolecular isomers investigated. Even at high generations, the dendrimers exhibited the most efficient energy transfer, thereby indicating that the dendritic architecture affords superior site isolation to the central porphyrin it surrounds. 相似文献
100.
Hetero Diels-Alder reactions of transient nitrosoamidines are reported. Transient nitrosoamidines are formed by oxidation of protected N-hydroxylguanidines and are trapped in situ by 1,3-dienes to give [4 + 2] cycloadducts in good yields and regioselectivity. The resultant cycloadducts are versatile intermediates for the formation of functionalized guanidines. [reaction: see text] 相似文献