Use of tetrahydropyrimidinium salts for highly efficient palladium-catalyzed cross-coupling reactions of aryl bromides and chlorides

New, sterically demanding 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (2) as NHC precursors have been synthesized and characterized. These salts, in combination with palladium acetate, provided active catalysts for the cross-coupling of aryl chlorides and bromides under mild conditions. The catalytic system was applied to the Heck, Suzuki and benzaldehyde (Kumada) coupling reactions. Catalyst activity was found to be influenced by the presence of a methoxy group on the ring of the p-position of benzyl substituent of the ligand precursor.     

Spectrophotometric determination of hydrazines withperi-naphthindan-2,3,4-trione hydrate

Summary A new micromethod for spectrophotometric determination of hydrazine compounds is described. It is based on a reaction withperi-naphthindan-2,3,4-trione hydrate at pH 2.5 to give a red precipitate of dihydroxy-peri-naphthindenone which is dissolved in methanol and measured at 460 nm. The results obtained show an average recovery of 99.8 %, the precision being ± 1 %.

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Zusammenfassung Eine neue Mikromethode zur spektrophotometrischen Bestimmung von Hydrazinverbindungen wurde beschrieben. Sie beruht auf der Reaktion mit peri-Naphthindan-2,3,4-trion-hydrat bei pH 2,5, wobei ein roter Niederschlag von Dihydroxy-peri-naphthindenon entsteht, der in Methanol gelöst und bei 460 nm gemessen wird. 99,8% Substanz werden wiedergefunden, die Genauigkeit beträgt ±1%.

     

The potential of serially coupled alkyl-bonded silica monolithic columns for high resolution separations of pharmaceutical compounds in biological fluids

Summary In this paper we investigate the potential of alkyl-bonded silica monolithic columns for the isolation and identification of drug-related components in biological fluids. Up to 6 columns have been connected in series to produce a chromatographic system with up to 40,000 plates. This high-resolution chromatography system has been coupled to both MS and NMR to enable efficient detection and characterisation of drug-related components in biological fluids. The use of six coupled columns has been shown to give enhanced resolution over a high quality silica particulate column packed with 3 μm material which exhibits the same back pressure. The effect of volume and mass load on the performance of monolithic columns for semi-preparative chromatography of biological fluids has also been investigated. In these studies it was possible to inject up to 100 mL of neat urine with no loss of chromatographic performance. Furthermore, upon re-testing, the columns showed similar chromatographic performance. Again several columns were serially connected, producing enhanced resolution in the semi-preparative mode.     

Synthesis and spectroscopic studies of methoxy-substituted phenylthienylnicotinamidines

Abstract

Five thienylnicotinamidine derivatives 5a–e were prepared from their corresponding nicotinonitriles 3a–e on treatment with lithium trimethylsilylamide [LiN(TMS)₂] followed by hydrolysis using ethanolic/HCl (gas). The nicotinonitriles 3a–e were prepared via Suzuki coupling reaction of bromothienyl derivative 1 with the appropriate phenylboronic acids 2a–e. The DFT calculation was used to optimize the geometric structure of the newly synthesized nicotinamidines. The comparison of DFT/B3LYP calculated spectral data (¹H-NMR and ¹³C-NMR) with the experimental data showed acceptable agreement. Mass fragmentation patterns of 3,4-dimethoxyphenyl, 3,5-dimethoxyphenyl, and 3,4,5-trimethoxyphenyl thienylnicotinamidine derivatives were investigated.     

Intramolecular energy-transfer in a europium(III) chelate with salicylidene-valinate schiff base

Summary An intense fluorescence,⁵D⁷F, of the europium(III) ion was observed at room temperature in DMSO and DMF solutions of the europium(III) chelate with salicylidene-valinate Schiff base, as a result of an intramolecular energy-transfer from the ligand to the metal ion. The metal chelate has been characterized and appears to possess an octahedral configuration. These results offer an interesting opportunity to probe the active sites of pyridoxal enzymes.     

The anionic alkylation of easily reducible arenes. A photochemical route to nucleophilic aromatic substitution of anthracene by organolithiums

High yield nucleophilic addition ensues upon mixing tetrahydrofuran solutions of benzyllithium or cyclooctadienyllithium and anthracene at low temperatures At least part of this addition proceeds by a single electron transfer pathway. Photolysis of the resulting adducts leads to the elimination of lithium hydride, giving net nucleophilic substitution in approximately 50% yield. The analogous reaction fails with naphthalene, where photolysis of the organolithium/ arene mixture leads to dimeric products derived from the organolithium.     

Atomic absorption spectrometric and potentiometric microdetermination of the nitro and nitroso groups in organic compounds

New simple, rapid, accurate, and selective methods are described for microdetermination of the nitro and nitroso groups in organic compounds. These are based on reduction with cadmium metal and 0.05 M HCl whereby 6 and 4 equivalents of the cadmium ions are released per nitro and nitroso groups, respectively. The cadmium ions are measured by atomic absorption spectrometry at 228.8 nm, potentiometrically by titration with EDTA using the cadmium ion selective electrode, and visually by EDTA titration using Eriochrome Black T indicator. Results with an average recovery of 98% and a mean standard deviation of 1.3% are obtainable and no interferences are caused by many nitrogen, oxygen, and sulfur functional groups.     

Th,U and trace elements determination in Egyiptian Lake sediments by INAA and laser fluorimetry

A study was undertaken to determine element concentrations in Aswan High Dam Lake sediments. Sediment samples were collected from 40 to 500 km upstream of the dam to follow the sedimentation process and the distribution of Th, U and the trace elements in the lake. INAA was applied for the determination of Sm, Ce, Lu, Th, Cr, Yb, Au, Hf, Ba, Nd, Cs, Tb, Sc, Rb, Fe, Zn, Co, Eu, and Sb, while Laser Fluorimetry was applied for U determination. The accuracy and the reproducibility of the techniques were tested with IAEA standard materials (SL, Soil-7). The U values ranged from 4 ppm to 18 ppm, Th values were between 2 and 10 ppm, and showed a very good correlation with the rare earth elements and Fe. The distribution of most of the elements in the lake follows the same trend as the distribution of the clays in the sediments. Ba showed a negative correlation with most of the elements under investigation.Paper presented at the 3th International Conf. on Nuclear and Radiochemistry (NRC-3), Vienna, 1992.     

Selective kinetic determination of pyridoxal-5'-phosphate with an ammonia gas-sensing electrode

The coenzyme pyridoxal-5'-phosphate (PLP) is deiermined by in situ measurement of the rate of ammonia production using a potentiometric gas-sensing membrane electrode. It is shown that the initial rate of ammonia liberation from L-tryptophan by action of tryptophanase apoenzyme and the coenzyme can be linearly related to PLP levels in the nanogram range with minimal interference from related compounds. Calibration data for the 1 × 10^-7–2.5 × 10^-6 M range for PLP yielded a least-squares equation of rate (mV min^-1) = (0.64 ± 0.01) C — 0.01 ± 0.02 with a standard error of 0.02 mV min^-1, where concentration, C, is expressed in units of 10^-7 mol l^-1.