Laccase-catalyzed carbon-carbon bond formation: oxidative dimerization of salicylic esters by air in aqueous solution

The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated.     

Ion Chromatographic determination of trace anions and cations in high-purity water

An ion chromatographic measuring system for the off-line and on-line determination of some trace anions and cations in high-purity water is presented. The ng/L level of anions and cations in 20-130 mL high-purity water can be analyzed after preconcentration on ion exchange columns. The concentrated solutes are eluted by eluents from the trap column and separated using a Dionex analytical column. The quantification of each ion is achieved using the suppressor technique and conductivity detector. The influence of various parameters on the results is discussed. The detection limits of cations and anions are between 10 and 30 ng/L for chloride, bromide, nitrate, phosphate, sulphate, sodium, ammonium, potassium, magnesium and calcium ions.     

High-performances membranes for pervaporation I. Poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) blends

Dense membranes were prepared from poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) (PVA–PVP) blends of different compositions and studied in swelling and dehydration by pervaporation of three organic solvents contaminated by 5 wt% water. The swelling generally increases with the PVP content. No extraction occurs in water–tetrahydrofuran (THF) and water–methyl ethyl ketone (MEK) mixtures. In ethanol containing 10 wt% of water, there is no extraction for blends containing less than 40 wt% PVP and an increasing extraction beyond this PVP content. The pervaporation flux of the water–ethanol mixture increases drastically at the same threshold whereas the water permselectivity falls to a low level. The values of the diffusion and permeability coefficients determined from transient permeation of the test water–ethanol mixture exhibit a similar sudden increase at the same PVP content threshold. This singular behavior of the blend membranes is interpreted by a strong affinity of the PVP component to ethanol, combined with a disappearance of crystallites in the blend at this threshold. Consequently the amorphous membrane can swell freely according to the affinity of the PVP component, leading to the observed behavior.     

Action des bromures de perfluoroalkylmagnésiums sur les aldéhydes α,βéthyléniques

Perfluoroalkylmagnesium bromide, C_nF_2n+1MgBr (n = 2, 6, 8), reacts with α,β-unsaturated aldehydes to give allylic alcohols as the sole products. No attack on the β-carbon atom of the carbonyl was detected, even when the reaction was carried out in the presence of CuCl. Part of the Grignard reagent decomposes to trans-R_FCFCFBr and trans-R_FCFCFI. Neither a mechanism involving dissociation into R⁺_F MgX^- nor the formation of a carbene intermediate is capable of explaining the thermal decomposition of the Grignard reagent.     

Further theoretical studies of the structure and electronic spectrum of cyclobutadiene

The possible geometries for cyclobutadiene and the electronic spectra corresponding to those geometries were calculated by a modified Pariser-Parr method with inclusion of doubly-excited as well as singly-excited configurations in calculating the -energy. The bond lengths of the most stable forms agreed well with previous calculations where the empirical parameters used in the -energy calculation were different from those used here, and where only singly-excited configurations were included. With these additional refinements, the rectangular singlet is calculated to be more stable than the square triplet. It is noted that the geometry predicted to have the lowest energy is a function of the approximations employed.

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Zusammenfassung Mögliche Geometrien und die zugehörigen Spektren von Cyclobutadien wurden nach Pariser-Parr unter Einschlu\ der einfach und zweifach angeregten Konfigurationen berechnet. Die BindungslÄngen der stabilsten Form stimmen gut mit früheren Rechnungen mit anderen gewÄhlten Parametern überein, bei denen nur die einfach angeregten Konfigurationen berücksichtigt worden waren. Und zwar ergibt sich, da\ eine rechteckige Form (Singulett) stabiler als die quadratische (Triplett) ist. Allerdings hÄngt diese Geometrie von den gewÄhlten Parametern ab.

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Résumé Les geometries possibles du butadiéne et les spectres électroniques correspondants ont été calculés par une méthode de Pariser-Parr motifiée avec interaction de configurations avec les états mono et diexcités des électrons . Les longueurs de liaison des formes les plus stables sont en accord avec celles obtenues précédemment avec des paramètres empiriques différents dans un calcul ne tenant compte que des configurations monoexcitées. Dans notre calcul amélioré le singulet rectangulaire est plus stable que le triplet carré. La géométrie la plus stable dépend de l'approximation utilisée.

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This research was supported in part by Research Grant GP 4290 from the National Science Foundation.     

Motion of foam films in diverging-converging channels

Existing theories of the motion of foam films in capillaries often assimilate the pressure drop over the foam films to the static capillary pressure obtained from the Young-Laplace equation. Hence, they ignore the contribution of dynamic effects associated with the rapid stretching and contraction of the foam films to the overall viscous dissipation. This paper reports an investigation of the motion of foam films in axisymmetric diverging-converging channels, taking into account surface viscosity and elasticity. First, a phenomenological theory for the motion of the foam films is developed using simple physical arguments. We show that the displacement of the film obeys a nonlinear second-order differential equation, which can be solved numerically for the (dimensionless) distance from the inlet and the pressure drop as a function of time. Experiments with foam film motion, conducted using glass diverging-converging channels (minimum radius = 3.00 +/- 0,01 mm, maximum diameter = 7,98 +/- 0,01 mm) and nitrogen foam stabilized with sodium dodecyl sulfate (SDS) in brine, are discussed. For a single film motion in the diverging channel, we find that (a) the static pressure drop is a concave-upward function of distance and decreases from 1.0 to about 0.3, whereas (b) the dynamic pressure drop is concave downward and increases from 1 to a maximum of 1.3 and then decreases to 0.7. In the converging channel both the static and dynamic pressure drops are concave-downward functions, but the dynamic pressure drop values are always higher than the static ones. For two films the motions were found to be rather sensitive to the initial arrangement in the channel. The experiments are found to be in excellent agreement with the theoretical predictions. These observations imply that the large flow resistance obtained during foam flow in granular porous media, where converging-diverging channels are abundant, is largely due to the surface elasticity and viscosity of the films.     

Synthesis of a model system for the preparation of phloroglucinol containing natural products

A model system for the synthesis of phloroglucinol containing natural products was synthesized. Key steps include a manganic acetate-mediated cyclization and the facile conversion of an alkene into a β-bromoenone.     

Application of thermo-electrochemistry to simultaneous leaching of sphalerite and MnO2

In order to enhance the electrogenerative leaching rate of sphalerite reasonably, the basic principle of generative process was applied to the simultaneous leaching of sphalerite in the presence of MnO₂. It was confirmed by experimental results that both mental ions and electric energy could be obtained in the simultaneous electrogenerative leaching process. The leaching cell had the open circuit potential about 1.0 V, about 2000 C of electric quantity was obtained, the optimal leaching ratio of Zn²⁺ and Mn²⁺ was 48.5, 39.6% respectively, after electrogenerative leaching for 11 h.     

Determination of total phosphorus and nitrogen in turbid waters by oxidation with alkaline potassium peroxodisulfate and low pressure microwave digestion, autoclave heating or the use of closed vessels in a hot water bath: comparison with Kjeldahl digestion

The evaluation of the use of alkaline peroxodisulfate digestion with low pressure microwave, autoclave or hot water bath heating for the determination of total phosphorus and nitrogen in turbid lake and river waters is described. The efficiency of these digestion procedures were compared to a Kjeldahl digestion procedure with sulphuric acid-potassium sulfate and copper sulfate. The final solution before digestion was 0.045 M in potassium peroxodisulfate and 0.04 M in sodium hydroxide. Procedures were evaluated by the analysis of suspensions of two reference materials, National Institute of Environmental Science, Japan, no. 3 Chlorella and no. 2 pond sediment and natural turbid waters. Best recoveries of phosphorus and nitrogen by microwave heating were obtained when solutions were digested at 95 °C for 40 min. Quantitative recoveries of phosphorus from Chlorella suspensions up to 1000 mg/l were obtained by all three heating procedures, but incomplete recoveries of nitrogen occurred above 20 mg N/l in the digested sample. Good recoveries of phosphorus and nitrogen from suspended sediment suspensions were obtained only from solutions containing <150 mg/l of suspended sediments. Recoveries of phosphorus from phosphorus compounds containing COP and CP bonds added to distilled water were quantitative (94-113%) except for polyphosphates (microwave, 34±8; autoclave, 114±6; water bath, 96±4) and aluminium phosphate (8-23%). Recoveries of nitrogen compounds containing CN bonds added to distilled water were quantitative (94-96%). The analysis of a range of natural turbid water samples by alkaline peroxodisulfate and microwave, autoclave and water bath heating gave similar total phosphorus and nitrogen results. All procedures using alkaline peroxodisulfate underestimate phosphorus concentrations at high suspended sediment concentrations (>150 mg/l) and are only suitable for the analysis of very turbid samples when the turbidity is due to organic matter (algal cells, plant detritus). Underestimation of nitrogen occurs when samples contain more than 20 mg N/l.     

Synthesis of aromatic polythioamide-oxothioxoquinazolines from bis(1,3,4-thiadiazoline-5-thione) and aromatic bis-o-amino esters

Aromatic polythioamide-oxothioxoquinazolines were synthesized by the polycondensation of 2,2′-(m-phenylene)bis-1,3,4-thiadiazoline-5-thione with aromatic bis-o-amino esters. The polymerizations were carried out at 160°C in acidic media such as m-cresol, sulfolane, and polyphosphoric acid to produce polymers with reduced viscosities up to 0.5 dL/g. These polymers were soluble in polar aprotic solvents like N-methyl-2-pyrrolidone and some acidic media including m-cresol. The polythioamide-oxothioxoquinazolines showed relatively good thermal stability with 10% weight loss at 344–394°C in air.