排序方式: 共有73条查询结果,搜索用时 31 毫秒
21.
J. Ballesta Claver 《Analytica chimica acta》2004,522(2):267-273
We have developed a selective and reusable chemiluminescent test strip to determine hypochlorite. The hypochlorite-sensitive test strip contains a 10 mm × 9 mm piece of anionic cellulose paper in fluoresceinate cycle, glued to a 10 mm × 4 cm × 0.5 mm polyester strip. The measurement of the chemiluminescence in a luminometer when 1 ml of sample is injected into a conventional cell containing the strip makes it possible to determine hypochlorite. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The test strip responded linearly to hypochlorite over two linear ranges, the first 2.0-10.3 mg L−1 and the second 10.3-51.4 mg L−1, with a detection limit of 0.4 mg L−1. The reproducibility using the same disposable test strip at a medium level of the range was 6.6%, as relative standard deviation (R.S.D.), and 12.3% using different test strips. The procedure was applied to the determination of hypochlorite in different types of waters. 相似文献
22.
Carmen Claver Esther Marco Luis A. Oro Miguel Royo Eitel Pastor 《Transition Metal Chemistry》1982,7(5):246-249
Summary Complexes [Rh(COD)(L-L)]ClO4 are prepared by reaction of [Rh(COD)2]ClO4 with the appropriate ligand L-L (4,7-Ph2Phen, 2,9-Me2-4,7-Ph2Phen, 2,9-Me2Phen or 5,6-Me2Phen). Treatment of these complexes with carbon monoxide gives [Rh(CO)2(L-L)]ClO4. When the carbonylation reaction is performed in the presence of P(4-RC6H4)3, pentacoordinate complexes [Rh(CO)(L-L){P(4-RC6-H4)}3
2]ClO4 (R=Me, H, F or Cl) are formed. The use of [Rh(COD)(L-L)]ClO4 as homogeneous hydroformylation catalyst precursors was studied (50 atm, 80°C). Under these conditions no hydrogenation of the olefin or of the aldehydes is observed, but isomerisation reactions are significant. 相似文献
23.
Jansat S Gómez M Philippot K Muller G Guiu E Claver C Castillón S Chaudret B 《Journal of the American Chemical Society》2004,126(6):1592-1593
Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system. 相似文献
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25.
Bastero A Claver C Ruiz A Castillón S Daura E Bo C Zangrando E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(15):3747-3760
Continuing our studies into the effect that N-N' ligands have on CO/styrene copolymerization, we prepared new C(1)-symmetrical pyridine-imidazoline ligands with 4',5'-cis stereochemistry in the imidazoline ring (5) and 4',5'-trans stereochemistry (6-10) and compared them with our previously reported ligands (1-4). Their coordination to neutral methylpalladium(II) (5 a-10 a) and cationic complexes (5 b-10 b), investigated in solution by NMR spectroscopy, indicates that both the electronic and steric properties of the imidazolines determine the stereochemistry of the palladium complexes. The crystal structures of two neutral palladium precursors [Pd(Me)(2-n)Cl(n)(N-N')] (n=1 for 8 a; n=2 for 9 a') show that the Pd-N coordination distances and the geometrical distortions in the imidazoline ring depend on the electronic nature of the substituents in the imidazoline fragment. Density functional calculations performed on selected neutral and cationic palladium complexes compare well with NMR and X-ray data. The calculations also account for the formation of only one or two stereoisomers of the cationic complexes. The performance of the cationic complexes as catalyst precursors in CO/4-tert-butylstyrene copolymerization under mild pressures and temperatures was analyzed in terms of the productivity and degree of stereoregularity of the polyketones obtained. Insertion of CO into the Pd-Me bond, which was monitored by multinuclear NMR spectroscopy, shows that the N ligand influences the stereochemistry of the acyl species formed. 相似文献
26.
Oscar Pàmies Aurora Ruiz Gemma Net Carmen Claver Hermann Kalchhauser Michael Widhalm 《Monatshefte für Chemie / Chemical Monthly》2000,131(11):1173-1179
Summary. The chiral diphosphine ligand xylophos (1) was tested as an auxiliary in palladium catalyzed allylic substitution reactions. Whereas its activity was found to be generally
good only in the case of 1,3-diphenylprop-2-en-1-yl acetate, a fair level of asymmetric induction was achieved with sodium
dimethyl malonate (83%ee) and benzylamine (66%ee) as nucleophiles.
Received June 13, 2000. Accepted July 3, 2000 相似文献
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28.
Muñoz-Moreno BK Claver C Ruiz A Bianchini C Meli A Oberhauser W 《Dalton transactions (Cambridge, England : 2003)》2008,(20):2741-2750
The diphosphine 3,5-dideoxy-1,2-O-isopropylidene-3,5-bis(di(2-methoxyphenyl)phosphanyl)-alpha-D-xylofuranose (o-MeO-xylophos), which differs from the known 3,5-dideoxy-1,2-O-isopropylidene-3,5-bis(diphenylphosphanyl)-alpha-D-xylofuranose (xylophos) by the presence of 2-methoxy substituents on the P-aryl rings, has been synthesized and characterized. These two ligands have been employed to stabilize the Pd(II) complexes [PdCl2(o-MeO-xylophos)] (1a), [PdCl2(xylophos)] (2a), [PdClMe(o-MeO-xylophos)] (1b), [PdClMe(xylophos)] (2b), [Pd(OTs)(H2O)(o-MeO-xylophos)](OTs) (1c) and [Pd(OTs)(H2O)(xylophos)](OTs) (2c). All complexes have been characterized by multinuclear-NMR spectroscopy. The solid-state structure of 1a has been determined by a single crystal X-ray analysis. The Pd-aqua complexes 1c and 2c have been employed to catalyse the CO-ethene and CO-propene copolymerization as well as the CO-ethene-propene terpolymerization reaction in MeOH. The catalytic activity and the molecular weight of the polyketones have been compared to those of the products obtained with analogous catalysts, [Pd(H2O)2(o-MeO-dppp)](OTs)2 (3c) and [Pd(H2O)(OTs)(dppp)](OTs) (4c), bearing the classical 1,3-bis(diphenylphoshino)propane ligand (dppp). Under comparable catalytic conditions, all catalysts produce structurally similar polymeric materials, with 1c yielding the largest propene incorporation as well as the highest productivity of low-molecular-weight terpolymers. 相似文献
29.
Muñoz BK Godard C Marinetti A Ruiz A Benet-Buchholz J Claver C 《Dalton transactions (Cambridge, England : 2003)》2007,(47):5524-5530
Palladium complexes bearing phospholane 1 and phosphetane 2-4 ligands have been synthesised to be used as catalyst precursors in the asymmetric methoxycarbonylation of vinyl arenes. Single crystals of the complex [PdCl2(2)2] II were obtained from a toluene solution and analysed by X-ray crystallography. Using these complexes, excellent regioselectivity (up to 99%) to the branched esters was obtained. Phosphetane ligands provide higher enantioselectivity than the phospholane under the same reaction conditions and an important influence of the substrate was observed. Enantioselectivity up to 50% was obtained using 4-methoxystyrene. 相似文献
30.
[reaction: see text] A series of phosphite-phosphoroamidite ligands, derived from readily available d-xylose, has been successfully applied for the first time in the Pd-catalyzed allylic substitution of several substrates with different steric and electronic properties, with high enantioselectivities (ee's up to 98) and activities in standard conditions. 相似文献