Mechanism of the solid state reaction NaCl + KF → NaF + KCl

The mechanism of the solid state displacement reaction NaCl + KF → NaF + KCl was investigated, employing diffusion couples (single crystals), in air at 550°C.The product layer obtained was formed with NaF and (Na, K)Cl solid solution.From cation concentration profiles, photometrically determined, for the NaClz.sfnc;KF and NaCl|KCl systems after annealing at 550°C, and from X-ray diffraction analysis on product layer surfaces for the NaCl|KF system, it was possible to state that the overall process is governed by a cation-counterdiffusion mechanism.A comparison between the diffusion coefficient evaluated through the rate constant and that calculated by means of the Boltzmann-Matano analysis for the system NaClKCl, allows one to deduce that the cations Na⁺ and K⁺ are transported in the (Na, K)Cl solid solution.     

Kinetics and mechanism of the solid state reaction TlCl + KI → TlI + KCl

The kinetics of the solid state displacement reaction TlCl + KI → TlI + KCl was investigated by the diffusion couple method (using single crystal disks and pellets) in the temperature range 215–300°C. Two distinct layers are present: the first, in contact with TlCl, formed by a solid solution of TlI in TlCl, grows with a linear rate; the second, in contact with KI, formed by two solid solutions of TlCl in TlI and in KCl, respectively, grows according to the parabolic law. From marker experiments and X-ray analyses on product layer surfaces parallel to the original interface, along with a comparison of the rate constants and the diffusion coefficients, it was possible to deduce that the overall process is governed by diffusion of Tl⁺ and Cl^? in the iodide-rich solid solution Tl(I, Cl) and that the rate-determining step is the diffusion of Tl⁺.     

Thermogravimetric and calorimetric evaluation of babassu biodiesel obtained by the methanol route

The growing petroleum deficit requires the development of alternative fuel sources. Biodiesel is a good alternative, as it is a biodegradable and renewable product, which obeys the carbon cycle. In this work, the biodiesel from babassu was synthesized using the methanol route, and characterized by physico-chemical analyses in order to make able the investigated biodiesel to fulfill with its properties the requirements of Brazilian National Agency for Petroleum, Natural Gas and Biofuel (ANP). Besides gas chromatography, IR spectroscopy experiments and thermoanalytical measurements in air and in nitrogen were done to determine the main thermal decomposition processes and calorimetric events. The evaporation temperature of babassu biodiesel was similar in both atmospheres, started around 52 in air and around 60°C in nitrogen.     

Spectral assignments of new diterpenes from Hyptis martiusii Benth

The structural characterization of two new abietanes and a new spiro-fused tricyclic diterpene isolated from the roots of Hyptis martiusii is described. The first member of a new class of rearranged abietane diterpenoids designated martiusane was characterized by the use of 1D NMR and several 2D shift correlated NMR pulse sequences (1H,1H-COSY, HMQC, HMBC and NOESY). Unambiguous 1H and 13C chemical shift assignments for all compounds are reported.     

Highly stereospecific palladium-catalysed vinylation of vinylic halides under solid-liquid phase transfer conditions.

(E,E) and (E,Z) conjugated dienoates, dienones and dienals are obtained with high stereospecificity (?95%) and in high yields from the corresponding (E) and (Z) vinylic halides and vinylic substrates (methyl acrylate, methyl vinyl ketone or acrolein), in the presence of potassium carbonate, tetrabutylammonium chloride and a catalytic amount of palladium acetate, in N,N-dimethylformamide at room temperature.     

Molecular modeling of freezing of simple fluids confined within carbon nanotubes

We report Monte Carlo simulation results for freezing of Lennard-Jones carbon tetrachloride confined within model multiwalled carbon nanotubes of different diameters. The structure and thermodynamic stability of the confined phases, as well as the transition temperatures, were determined from parallel tempering grand canonical Monte Carlo simulations and free-energy calculations. The simulations show that the adsorbate forms concentric molecular layers that solidify into defective quasi-two-dimensional hexagonal crystals. Freezing in such concentric layers occurs via intermediate phases that show remnants of hexatic behavior, similar to the freezing mechanism observed for slit pores in previous works. The adsorbate molecules in the inner regions of the pore also exhibit changes in their properties upon reduction of temperature. The structural changes in the different regions of adsorbate occur at temperatures above or below the bulk freezing point, depending on pore diameter and distance of the adsorbate molecules from the pore wall. The simulations show evidence of a rich phase behavior in confinement; a number of phases, some of them inhomogeneous, were observed for the pore sizes considered. The multiple transition temperatures obtained from the simulations were found to be in good agreement with recent dielectric relaxation spectroscopy experiments for CCl(4) confined within multiwalled carbon nanotubes.     

Analysis of methylglyoxal in water and biological matrices by capillary zone electrophoresis with diode array detection

We describe a new method for the determination of methylglyoxal in water and biological matrices, using o-phenylenediamine as derivatizing agent and solid-phase extraction followed by capillary zone electrophoresis with diode array detection. 25 mM sodium phosphate running buffers at pH 2.2, 30 kV, and 25 degrees C allowed the best instrumental conditions for the optimum separation of methylglyoxal in a suitable analytical time (< 10 min), using an uncoated fused-silica capillary of 75 microm inner diameter and an effective length of 45.1 cm with an extended light path and the wavelength set to 200 nm. Under optimized instrumental conditions, good reproducibility of the migration time (< 1.1%), precision (< 5%), an excellent linear dynamic range from 0.1 to 3.6 mg/L (r(2) = 0.9997), and low limits of detection (7.2 microg/L) were obtained for methylglyoxal measurements, using the internal standard methodology. Assays on laboratory-spiked tap and ground water samples allowed a remarkable accuracy, presenting yields of 95.0 +/- 4.3 and 94.0 +/- 1.1%, respectively, and good performance to determine methylglyoxal in beer and yeast cells suspensions matrices was also obtained at trace level. The present methodology is a cost-effective alternative for routine quality control analysis, showing to be reliable, sensitive, and with a low sample volume requirement to monitor methylglyoxal in water and biological matrices.     

Determination of atracurium and laudanosine in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method coupled with fluorometric detection has been developed for the determination of atracurium and its major end-product laudanosine in human plasma. The method enables good separation of atracurium from its metabolites after direct precipitation of plasma proteins. The assay is sensitive, reproducible and linear for atracurium concentrations ranging from 31.25 to 8000 ng/ml. In a clinical setting, drugs commonly administered during anesthesia did not interfere with the assay. This method provides a simple and time-saving alternative to existing methods.     

Réaction du diméthylcuprate de lithium avec les dérivés carbonylés α,β-insaturés α-fluorés et α-chlorés

Depending on the nature of the halogen, α-fluoro- and α-chloro-α,β-unsaturated carbonyl compounds (whose reduction potentials are greater than ? 2.4V) react in different ways with lithium dimethylcuprate. With α-fluoro derivatives, both 1,2- and 1,4-addition is observed, their ratios depend on the steric hindrance of the β-position. 1,4-Addition products are obtained from aldehydes and β-monosubstituted α-chloro-α,β-ethylenic ketones and esters. β,β-Disubstituted α-chloro ketones and esters give only reduction of halogen via halogen-metal exchange.