Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.     

Enthalpies of formation of methoxybenzoic acids and their dependence on structure

The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements betweenT=270 K andT=338 K were carried out by DSC. From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono- and dimethoxy-benzoic acids have been completed. Their_f H _m ^o values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ·mol^–1 was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy—the so-called buttressing effect—was evaluated (2–24 kJ· mol^–1 for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the C_ar-O bond.     

Cure kinetics of epoxy resin and thermoplastic polymer

The cure kinetics and morphology of diglycidyl ether of bisphenol A (DGEBA) modified with polyvinyl acetate (PVAc) using diaminodiphenylmethane (DDM) as hardener were investigated through differential scanning calorimetry (DSC) and environmental scanning electron microscopy (ESEM). Isothermal curing measurements were carried out at 150, 120 and 80°C. The kinetic parameters were obtained using the general autocatalytic chemically controlled model. The comparison of the kinetic data indicates that the presence of PVAc does not change the autocatalytic nature of the cure reaction. Two T _g’s were observed in the fully cured samples of the modified systems. ESEM micrographies confirm the biphasic morphology.     

Complexation of Ni (II) and Zn(II) ions by 3-(1-naphthyI)-2-mercaptopropenoic acid

The complexation equilibria between Ni(II) and Zn(II) metal ions with 3-(1-naphthyl)-2-mercaptopropenoic acid (H₂NMP) were studied by glass electrode potentiometry, at 25 °C and 1.0 mol·dm^–3 in NaClO₄ as constant ionic medium in 50% (v/v) water-ethanol solutions. Formation constants for the complexes Ni(NMP), Ni(NMP) ₂ ^2– , Zn(NMP) and Zn(NMP) ₂ ^2– , refined by the MINIGLASS program, are reported.     

Some observations on the automation by flow injection analysis of the spectrophotometric determination of amino acids and proteins witho-phthalaldehyde

Automation by flow injection analysis with Spectrophotometric detection of the determination of total amino acids and proteins witho-phthalaldehyde is not straightforward. The use of spectrophotometry, instead of spectrofluorimetry, and of N-acetyl-L-cysteine, instead of the conventional mercaptoethanol is advantageous because of the lower variability of absorptivities with respect to fluorescence yields, and the larger stability of the derivatives. Under adequate working conditions and with leucine as reference, the procedure can be used for the evaluation of total amino acids. A similar procedure is proposed for the analysis of proteins in a sample. Limits of detection are 1 × 10^–5 M for amino acids, and 1 × 10^–6 M for proteins, respectively.     

The study of degradable polystyrene: Photolysis in solution and photo-oxidation in films

Radical copolymerization of styrene with benzalacetophenone or benzalacetone in bulk or in suspension yielded copolymers with as much as 10 wt% of carbonyl monomer. They were characterized by GPC, viscometry and spectroscopy. Photolysis of copolymers was investigated in benzene at 313 nm. Quantum yields for main chain scissions were about 0.005 and the life-time of the triplet state was 5 nsec. Photo-oxidation in films was followed by monitoring the decrease in molecular weight and by i.r. and emission spectra. Quantum yield for main chain scission in films was about 0.0002. During photooxidation in film, the molecular weight distribution widened. A new i.r.-band appeared at 3580 cm^?1 and the carbonyl band was spread between 1700 and 1800 cm^?1. In the emission spectra, the vibrational resolved emission (typical of the carbonyl chromophore) disappeared.     

Nachweis von Oxoverbindungen. IV

Zusammenfassung Enolisierende Oxoverbindungen, die eine - CH₂-CO- oder eine- CO-NH-NH-Gruppe enthalten, geben mit Diazoniumsalz eine Farbreaktion. Formaldehyd, Benzaldehyd, Nitrobenzaldehyde, Benzoin, Benzophenon usw. reagieren dabei nicht. 1,3-Diketone geben mit diazotiertem p-Nitroanilin zweierlei Färbungen, bei geringer Diazoniumsalzkonzentration eine rote, bei großem Überschuß eine blaue oder grüne Färbung. Die Reaktionsgeschwindigkeit ändert sich auch nach der Art des Diazoniumsalzes. Mit dieser Methode wurden selektive Nachweise für Oxoverbindungen ausgearbeitet. Acetonspuren können in Äthanol bzw. in Wasser oder in Methyläthylketon mit diazotiertem Anilin, 10^–3 % Acetessigsäureäthylester in Äthylacetat mit diazotiertem p-Phenetidin, 10^–5 % Acetylaceton in Aceton mit diazotiertem p-Nitroanilin, außerdem Acetaldehyd neben Formaldehyd, Acetylphenylhydrazin neben Acetanilid, mbzw. o- neben p-Nitroanilin nachgewiesen werden. Nach dem Absorptionsspektrum erwies sich das Reaktionsprodukt von Aceton mit diazotiertem p-Nitroanilin als eine Azoverbindung.

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Detection of Oxocompounds. IV

Summary Enolizing oxo-compounds, that contain a -CH₂-CO- or a -CO-NH-NH-group, yield a color reaction with diazonium salt. Formaldehyde, benzaldehyde, nitrobenzaldehyde, benzoin, benzophenone etc. however do not show this reaction. 1,3-diketones yield two kinds of color reactions with diazotizedp-nitraniline; a slight diazonium salt concentration yields a red coloration, while a large excess gives a blue or green coloration. Selective detections for oxo-compounds were developed with this method. Traces of acetone may be detected in ethanol or water or in methylethyl ketone by means of diazotized aniline, 10^–3% of acetoacetic ester can be detected in ethyl acetate by means of diazotizedp-phenetidine, 10^–5% acetylacetone in aldehyde, acetylphenylhydrazine in the presence of acetanilide,m- oro- in the presence ofp-nitraniline. Judging from the absorption spectrum, the reaction product from acetone and diazotizedp-nitraniline is an azo compound.

     

Prompt gamma activation analysis using a chopped neutron beam

A beam chopper has been developed at the cold neutron PGAA facility of the Budapest Research Reactor. In the open phase of the chopper the usual prompt gamma-spectrum is recorded, while in the decay phase short-lived decay lines can be collected with good counting statistics on an extremely low baseline. A series of elements has been measured with the chopped beam technique to assess the capabilities of the new technique. An archaeological sample was also examined, to demonstrate how spectral interferences can be resolved.     

Electrochemical Synthesis and Characterization of Nickel(II) Complexes with N‐2‐Pyridyl‐sulfonamide Ligands

Heteroleptic nickel(II) complexes [NiL₂L′] of a series of monoanionic and potentially bidentate N‐2‐pyridyl‐sulfonamide ligands [HL] and 2,2′‐bipyridine or 1,10‐Phenanthroline (L′) have been prepared by electrochemical oxidation of a nickel anode in an acetonitrile solution of the ligands. The complexes have been characterized by microanalysis, IR and electronic spectroscopy, magnetic measurements and LSI mass spectrometry. The crystal structure of [Ni(Ms6mepy)₂(bipy)] has been determined by x‐ray diffraction and shows the metal in an octahedral NiN₆ environment. Octahedral structures are also proposed for the other complexes with the N‐2‐pyridyl‐sulfonamide ligands acting as N,N′ or N, O bidentate systems, depending on the position of the methyl substituent on the pyridine ring.     

A scaled quantum mechanical force field for the sulfuryl halides. I. The symmetric halides SO2X2 (X=F, Cl, Br)

Force fields and vibrational wavenumbers were calculated for the molecules SO2X2 (X=F, Cl, Br) using DFT techniques. The previously available experimental data and assignments for SO2F2 and SO2Cl2 were compared with the theoretical results and revised, and new low temperature infrared and Raman data were obtained for SO2Cl2. These data were subsequently used in the definition of scaled quantum mechanics force fields for such molecules. Adjusted wavenumbers were also predicted for the still unknown SO2Br2. A comparison is made with results published for the VO2X2- anions.