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181.
Mikhail S. Novikov Alexander F. Khlebnikov Elena S. Sidorina Rafael R. Kostikov 《Journal of fluorine chemistry》1998,90(2):1553-119
2-Fluoropyrroles were synthesised via 1,3-dipolar cycloaddition of iminiodifluoromethanides derived from corresponding imines and difluorocarbene to dimethyl acetylenedicarboxylate. 相似文献
182.
Taw FL Mueller AH Bergman RG Brookhart M 《Journal of the American Chemical Society》2003,125(32):9808-9813
Cationic Rh(III) complex [Cp(PMe(3))Rh(SiPh(3))(CH(2)Cl(2))]BAr(4)' (1) activates the carbon-carbon bond of aryl and alkyl cyanides (R-CN, where R = Ph, (4-(CF(3))C(6)H(4)), (4-(OMe)C(6)H(4)), Me, (i)Pr, (t)Bu) to produce complexes of the general formula [Cp*(PMe(3))Rh(R)(CNSiPh(3))]BAr(4)'. With the exception of the (t)BuCN case, every reaction proceeds at room temperature (t(1/2) < 1 h for aryl cyanides, t(1/2) < 14 h for alkyl cyanides). A general mechanism is presented on the basis of (1) an X-ray crystal structure determination of an intermediate isolated from the reaction involving 4-methoxybenzonitrile and (2) kinetic studies performed on the C-C bond cleavage of para-substituted aryl cyanides. Initial formation of an eta(1)-nitrile species is observed, followed by conversion to an eta(2)-iminoacyl intermediate, which was observed to undergo migration of R (aryl or alkyl) to rhodium to form the product [Cp*(PMe(3))Rh(R)(CNSiPh(3))]BAr(4)'. 相似文献
183.
Zhivka J. Simeonova Kiril B. Gavazov Alexander V. Alexandrov 《Central European Journal of Chemistry》2006,4(2):258-265
The formation of a new ternary ion-associate complex of vanadium(V) with 2,3-dihydroxynaphthalene and iodonitrotetrazolium
chloride with a composition ratio of 1:2:1 is reported. The complex is quantitatively extracted from water into chloroform.
The molar absorptivity (ɛ) of the extract at λ
max=340 nm is 2.5 × 104 dm3/mol cm, and Beer’s law is obeyed for concentrations ranging from 0.1 to 0.9 μg/cm3 V(V). The following constants are determined: the extraction constant, the association constant, the distribution constant,
and the recovery factor. The effects of foreign ions and reagents are studied. A selective and sensitive method is developed
for determination of vanadium in steels. 相似文献
184.
185.
The [Co2(CO)8]-mediated retro-Diels-Alder reaction of the annelated barrelenes 1 afforded the 1H-indol-2(3H)-one derivatives 3 (Scheme 1), while the hydrobarrelene 4a , under the same conditions, was converted to the anilide 6 (Scheme 2); 4b remained unaffected. The direct irradiation of 1 led to the annelated cyclooctatetraenes 7 (Scheme 3). On irradiation in the presence of excess of [Fe(CO)5], 1a , 1b , and 4a gave the tricarbonyliron complexes 8 , 9 , and 11 , respectively (Schemes 3 and 4); under these conditions, 4b was inert. 相似文献
186.
Irina B. Svir Alexander I. Oleinick Richard G. Compton 《Journal of Electroanalytical Chemistry》2003,560(2):117-126
The simulation of transport to double microband electrodes in generator–collector mode is reported focusing especially on the ‘titration curve’ approach to electroanalysis in which a titrant is electrogenerated from a redox active precursor on the generator electrode and reacts homogeneously with the target analyte. The current on the detector electrode reflects the amount of titrant ‘surviving’ passage between the two electrodes. The form of the titration curve – plots of detector current as a function of generator current – is shown to be highly sensitive to the electrode kinetics of the redox couple driven at the generator electrode. Accordingly the naïve use of such methodology for analysis without accompanying simulation and kinetic analysis is fraught with danger. Use of the conformal mapping approach in combination with the ADI method for investigation of the ‘titration’ current distributions at the double band system gives fast and precise simulation of this and similar problems. Convergence analysis is described which allows for the automatic selection of the simulation grid size so as to obtain a chosen accuracy (for example 1%) of the current for all experimentally meaningful values of the geometrical and physico-chemical parameters of the system to be investigated. 相似文献
187.
Ryabov AD Otto S Samuleev PV Polyakov VA Alexandrova L Kazankov GM Shova S Revenco M Lipkowski J Johansson MH 《Inorganic chemistry》2002,41(16):4286-4294
Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes [PtCl(2)L(2)] (2, L = SOMe(2) (a), rac-SOMePh (b), R-SOMe(C(6)H(4)Me-4) (c), and SMe(2) (d)) to afford the corresponding platinacycles cis-(C,S)-[Pt(II)(C(6)H(3)-2-CR'=NOH-5-R)Cl(L)] (3, R, R' = H, Me) have been investigated. The reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent occurs noticeably faster than with sulfide complex 2d due to the fact that the sulfoxide is a much better platinum(II) leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formation of unreactive dichlorobis(N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenone oxime and suggests the importance of pseudocoordinatively unsaturated species for the C-H bond activation by Pt(II). A comparative X-ray structural study of dimethyl sulfoxide platinacycle 3b (R = R' = Me) and its sulfide analogue 3e (R = H, R' = Me), as well as of SOMePh complex 3c (R = H, R' = Me), indicated that they are structurally similar and a sulfur ligand is coordinated in the cis position with respect to the sigma-bound phenyl carbon. The differences concern the Pt-S bond distance, which is notably longer in the sulfide complex 3e (2.2677(11) A) as compared to that in sulfoxide complexes 3b (2.201(2)-2.215(2) A) and 3c (2.2196(12) A). Whereas the metal plane is practically a plane of symmetry in 3b due to the H-bonding between the sulfoxide oxygen and the proton at carbon ortho to the Pt-C bond, an S-bonded methyl of SOMePh and SMe(2) is basically in the platinum(II) plane in complexes 3c and 3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex 3b. An interesting structural feature of complex 3c is that the two independent molecules in the asymmetric unit of the crystal reveal an extremely short Pt-Pt contact of 3.337 A. 相似文献
188.
Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10?1–1 × 10?5 M sodium thiocyanate. 相似文献
189.
The reductive determination of cadmium and zinc is used to illustrate the effects of pulse repetition times in differential pulse voltammetry at solid electrodes. With 100-ms repetition times, signal-to-background ratio is shown to improve in flow-injection response studies at a copper-amalgam working electrode for both voltage scanning and amperometric operation, allowing scan rates up to 100 mV s?1, and detection limits of 0.07–0.15 ng for cadmium and zinc after deaeration of sample solutions. Peak widths at baseline in the range 12–30 s, depending on flow rate, are obtained in the flow-injection system for cadmium and zinc at working potentials of ?0.77 and ?1.27 V, respectively. Interferences occur when cadmium is in large excess over zinc, although the voltammetric peaks do not overlap. 相似文献
190.
The Incorporation of Titania into Modified Silicates for Solar Photodegradation of Aqueous Species 总被引:2,自引:0,他引:2
Lowell R. Matthews David Avnir Alexander D. Modestov Srinivasan Sampath Ovadia Lev 《Journal of Sol-Gel Science and Technology》1997,8(1-3):619-623
A new class of sol-gel-derived photocatalytic materials has been synthesized and used in solar-assisted photodegradation studies. The materials are comprised of a homogeneous dispersion of commercial TiO2 powder into silica and organically modified silicate (Ormosil) hosts. The efficiency of the photocatalytic properties of these TiO2-containing materials was determined by their relative performance in the solar photodecomposition of aqueous rhodamine B. The improved adsorption properties of the modified materials compared to commercial TiO2 increase the photodecomposition rate and the buoyancy properties, although excess hydrophobicity decreases the wetted section of the catalyst and its photocatalytic performance. These materials can be used as floatable catalysts for solar-assisted water purification. 相似文献