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41.
Ivette Garcia CastroAnnegret Tillack Christian G HartungMatthias Beller 《Tetrahedron letters》2003,44(15):3217-3221
The one-pot synthesis of several branched secondary aliphatic amines is described. Hydroamination of terminal alkynes with aliphatic primary amines in the presence of Cp2Ti(η2-Me3SiCCSiMe3) gives the corresponding aldimines as intermediates. Reaction of these in situ produced aldimines with organolithium reagents (n-BuLi, PhLi) provides the α-branched amines in an easy way in upto 78% overall yield. 相似文献
42.
For determination of phosphorus in samples of vegetable origin (leaves and wheat flour) decomposition by means of molten alkali is proposed. Two procedures have been studied, one with dry reagents including an auxiliary oxidant, and the other with initially moist alkali with no extra oxidant. The fusion product is easily soluble and produces a solution suitable for elemental analysis. The phosphorus is determined by the molybdenum blue method. The suggested mineralization is rapid, accurate and precise. 相似文献
43.
An electrochemical method for the simultaneous determinations of HgII concentration and total AsIII and AsV concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of AsV to AsIII, or oxidation of AsIII to AsV before stripping analysis takes place. Also, the method for the simultaneous determination of HgII concentration and AsIII concentration is described. Measurements were performed in 0.1 M HCl using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the HgII and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of AsV to AsIII or oxidation of AsIII to AsV decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents. 相似文献
44.
Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 104 – 106) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented. 相似文献
45.
The technique of constant-potential electrolysis at a stationary spherical electrode (hanging mercury drop) was investigated for the determination of the diffusion coefficient of Tl(I) in sodium citrate-sodium hydroxide medium and of Tl in mercury. Current-time curves, at controlled potential, were obtained, covering periods from 1 to 25 sec after the start of the electrolysis. The influence of applied potential, time of electrolysis, convection and shielding of the electrode was studied. 相似文献
46.
Garcia Ruano JL Alcudia A del Prado M Barros D Maestro MC Fernandez I 《The Journal of organic chemistry》2000,65(10):2856-2862
The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported. 相似文献
47.
Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP18 mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C18 SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C18 precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml−1 requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml−1). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained. 相似文献
48.
Martinez Alvarez R Herrera Fernandez A Chioua M Ramiro Perez P Villalba Vilchez N Guzman Torres F 《Rapid communications in mass spectrometry : RCM》1999,13(24):2480-2488
Several 5,6-dialkyl-2,4-diarylpyrimidines were prepared and their electron ionization (EI) mass spectra reported. The benzylic cleavage takes place easily together with an important McLafferty rearrangement. The involvement of the nitrogen atom appears to be important in the fragmentation of 5-methyl-substituted pyrimidines. In contrast, the 6-methyl-substituted pyrimidines undergo benzylic cleavage without hydrogen transfer. Thus, the difference in the mass spectrometric behaviour allows the identification of these isomeric compounds which, in contrast, exhibit only small differences in their NMR spectra. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
49.
Garcia Jarem R. Peres Laura O. Fernandes Mauro R. Gruber Jonas Nart Francisco C. 《Journal of Solid State Electrochemistry》2004,8(2):122-126
In this communication we describe the electrochemical synthesis of poly(2,5-dicyano-p-phenylenevinylene) (DCNPPV) polymer films on indium tin oxide substrates. We investigate the purity, morphology, absorption and emission properties of the film. The purity was checked by infrared spectroscopy. The film formed presented spectroscopic purity equivalent to the chemically prepared PPV that was dialyzed for one week. Scanning electron microscopy of the surface revealed a grain-like morphology. The absorption and emission spectra showed absorption and emission bands at 420 nm and 575 nm, respectively, with the absorption onset at 422 nm, which corresponds to an energy gap of 2.25 eV. The electrochemical determination of the energy gap gives 2.05 eV, thus quite close to the optical energy gap at the onset of absorption. The EA and IP were determined by electrochemical measurements and are 3.46 eV and 5.51 eV, respectively.
相似文献
Francisco C. NartEmail: |
50.
R. A. Cruz R. C. Castillo F. J. Garcia R. I. Reed 《Journal of mass spectrometry : JMS》1977,12(1):21-23
The mass spectra of [17-13C]phyllocladene and [3-13C]methylenecholestane have been examined. It is shown that there are some rearrangements at 70 e V as in the case of [17-13C]kaurene. However, no extensive randomization is evident at the molecular ion level. The results are interesting because very little is known about 13C randomization in polycyclic aliphatic hydrocarbons. The percentage retention of label was calculated for each ion. 相似文献