31P{1H}-n.m.r. as a tool for identification of ruthenium isomers containing PPh3 or 1,4-bis(diphenylphosphino)butane ligands. X-ray structures of the cis-{RuCl2(PPh3)2 [4,4′-(-X)2-2,2′-bipy]} complexes [X=-H, -Me, -SMe and (-Cl, -Me)]

A series of cis-{RuCl₂(PPh₃)₂[4,4-(X)₂-2,2-bipy]} [cis-chlorines; X=-H, -Me, -SMe, and (-Cl,-Me)] complexes have had their structures determined by single crystal X-ray diffraction. The geometry of these complexes, also determined in CH₂Cl₂ solution by ³¹P{¹H}-n.m.r. spectroscopy, showed that the chemical shifts for the phosphorus atoms are slightly dependent on the pKa of the 4,4-(-X)₂-2,2-bipy ligands.     

Asymmetric synthesis of 2H-azirines derived from phosphine oxides using solid-supported amines. Ring opening of azirines with carboxylic acids

A simple and efficient asymmetric synthesis of 2H-azirine-2-phosphine oxides 3 is described. The key step is a solid-phase bound achiral or chiral amine-mediated Neber reaction of beta-ketoxime tosylates derived from phosphine oxides 1. Reaction of 2H-azirines 3 and 11 with carboxylic acids 4 gives phosphorylated ketamides 5 and 12. Ring closure of ketamides 5 and 12 with triphenylphosphine and hexachloroethane in the presence of triethylamine leads to the formation of phosphorylated oxazoles 8 and 13.     

Splitless on-line coupling of capillary high-performance liquid chromatography,capillary electrochromatography and pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

A mixture of unsaturated fatty acid methyl esters was separated with a new splitless capillary set-up. With the employed apparatus configuration different capillary separation techniques such as capillary high-performance liquid chromatography (cHPLC), capillary electrochromatography (CEC) and pressurized capillary electrochromatography (pCEC) could be applied. The detection and identification of the sample compounds were accomplished by hyphenating these capillary separation techniques with nuclear magnetic resonance (NMR) spectroscopy using a novel configuration of the detection capillary set-up. Using modified electrokinetically driven separation techniques, the electric field was applied solely across the separation column. With this improved interface for capillary liquid chromatography-NMR on-line coupling, the stereochemical assignment of the cis and trans configuration of unsaturated fatty acids could be easily accomplished. Finally, the results of cHPLC-NMR, CEC-NMR and pCEC-NMR coupling experiments were compared.Dedicated to Professor Günter Häfelinger on the occasion of his 65th birthday     

Highly stereoselective Friedel-Crafts type cyclization. Facile access to enantiopure 1,4-dihydro-4-phenyl isoquinolinones

The present report describes a stereoselective synthesis of 1,4-dihydro-4-phenyl isoquinolinones 5 based on a stereoselective Friedel-Crafts type cyclization. Cyclization precursors 1 were prepared in two steps, from the readily available (S)-mandelic acid, in 60-80% overall yield. The stereoselective electrophilic cyclization was accomplished in 20-86% yield and with 20-97% ee. In the course of this work, the presence of the amide carbonyl was found to be particularly important to guarantee a stereospecific process during the electrophilic aromatic substitution.     

Analysis of organic acids in wines by Fourier-transform infrared spectroscopy

Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable.     

A universal temperature controlled membrane interface for the analysis of volatile and semi-volatile organic compounds

A universal temperature controlled membrane interface (TCMI) has been constructed for hollow-fibre membranes. The membrane temperature is controllable in the range -70 to 250 degrees C using an electric heater and a flow of cooled nitrogen or helium gas. Volatile and semi-volatile organic compounds may be detected either by continuous diffusion across the membrane or by in-membrane pre-concentration followed by thermal desorption into the detector. The TCMI interface is demonstrated in combination with mass spectrometry and GC-MS, for the determination of VOCs and SVOCs in aqueous and air samples and for the on-line monitoring of a bioreactor.     

Addition of carbon nucleophiles to cyclic N-acyliminium ions in SDS/water

The acid-catalyzed addition of 1,3-dicarbonyl compounds and activated olefins (silyl enol ethers and ethyl vinyl ether) to N-Boc-2-methoxypyrrolidine (1a) and N-Boc-2-methoxypiperidine (1b) in SDS/water medium is described. Good yields of the corresponding 2-substituted N-Boc pyrrolidines were generally observed from 1a while moderate yields prevailed from 1b.     

Kinetics and mechanism of the aminolysis of O-aryl S-methyl thiocarbonates

[reaction: see text] The reactions of secondary alicyclic (SA) amines and quinuclidines (QUI) with 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates (1 and 2, respectively) and those of SA amines with 2,3,4,5,6-pentafluorophenyl S-methyl thiocarbonate (3) are subjected to a kinetic study in aqueous solution, at 25.0 degrees C, and an ionic strength of 0.2 M (KCl). The reactions of thiocarbonates 1, 2, and 3 were followed spectrophotometrically at 400, 360, and 220 nm, respectively. Under amine excess, pseudo-first-order rate coefficients (k(obsd)) are found. Plots of k(obsd) vs amine concentration at constant pH are linear, with the slope (kN) independent of pH. The Br?nsted-type plots (log kN vs pKa of aminium ions) are linear for all the reactions, with slopes beta = 0.9 for those of 1 with SA amines and QUI, beta = 0.36 and 0.57 for the reactions of 2 with SA amines and QUI, respectively, and beta = 0.39 for the reactions of SA amines with 3. The magnitude of the slopes indicates that both aminolyses of 1 are governed by stepwise mechanisms, through a zwitterionic tetrahedral intermediate (T+/-), where expulsion of the nucleofuge from T+/- is the rate-determining step. The values of the Br?nsted slopes found for the aminolyses of thiocarbonates 2 and 3 suggest that these reactions are concerted. By comparison of the reactions under investigation between them and with similar aminolyses, the following conclusions arise: (i) Thiocarbonate 2 is more reactive than 1 toward the two amine series. (ii) The change of the nonleaving group from MeO in 4-nitrophenyl methyl carbonate to MeS in thiocarbonate 1 results in lower kN values. (iii) The greater reactivity of this carbonate than thiocarbonate 1 is attributed to steric hindrance of the MeS group, compared to MeO toward amine attack. (iv) The change of a pyridine to an isobasic SA amine or QUI destabilizes the T+/- intermediate formed in the aminolyses of 2. (v) The change of 4-nitrophenoxy to 2,3,4,5,6-pentafluorphenoxy or 2,4-dinitrophenoxy as the leaving group destabilizes the tetrahedral intermediate formed in the reactions with SA amines, changing the mechanism from a stepwise process to a concerted reaction.     

Selective extraction of benzoic acid from landfill leachate by solid-phase extraction and ion-exchange chromatography

In this work a simple method was described for selective extraction of benzoic acid from landfill leachate samples. The samples were submitted to solid-phase extraction (SPE) with XAD-4 resin as the stationary phase and ion-exchange chromatography (IEC) using the ion-exchange resin Amberlyst A-27. The instrumental analysis was performed by gas chromatography with mass spectrometric detection (GC-MSD). Benzoic acid was isolated, identified and quantified. The extraction process is rapid, simple and of low cost. It was also environmental friendly, that is, it was used a minimum amounts of hazardous organic solvents and produced also minimum quantities of residues.     

Kinetics and mechanism of the reactions of S-2,4-dinitrophenyl 4-substituted thiobenzoates with secondary alicyclic amines

[reaction: see text] The title reactions, in 44 wt % ethanol-water at 25.0 degrees C, exhibit slightly curved Br?nsted-type plots (log kN versus pKa of amines) with slopes beta1 = 0.1-0.44 (at high pKa) and beta2 ca. 0.7 (at low pKa). The magnitude of some of these slopes, together with the fact that the curvature center (pKa(0) = 9.5-10.8) does not change with the electronic effects of the benzoyl substituent, suggests that these reactions are not stepwise, but concerted.