Biphasic asymmetric hydroformylation and hydrogenation by water-soluble rhodium and ruthenium complexes of sulfonated (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl in ionic liquids

A biphasic catalytic system with water-soluble rhodium complexes of sulfonated (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (labeled as (R)-BINAPS) in ionic liquid BMI·BF₄ has been developed for the asymmetric hydroformylation of vinyl acetate under mild conditions. The corresponding ruthenium complexes have been investigated for the biphasic asymmetric hydrogenation of dimethyl itaconate. The biphasic asymmetric hydroformylation of vinyl acetate provided 28.2% conversion and 55.2% enantiomeric excess when BMI·BF₄–toluene was used as the reaction medium at 333 K and 1.0 MPa for 24 h. The biphasic asymmetric hydrogenation of dimethyl itaconate in BMI·BF₄–ⁱPrOH at 333 K and 2.0 MPa afforded 65% enantiomeric excess with an activity similar to the homogenous analogs. Both biphasic catalytic systems with (R)-BINAPS ligand could be reused several times without significantly decrease in the activity, enantio- and regio-selectivities. The effects of properties of ionic liquid, molar ratio of ligand to rhodium, temperature, pressure and reaction time have been discussed.     

Sieve mechanism of microfiltration separation

A theoretical model of dead-end microfiltration (MF) of dilute suspensions is proposed. The model is based on a sieve mechanism of MF and takes into account the probability of membrane pore blocking during MF of dilute colloidal suspensions. An integro-differential equation (IDE) that includes both the membrane pore size and the particle size distributions is deduced. According to the suggested model a similarity property is applicable, which allows one to predict the flux through the membrane as a function of time for any pressure, and dilute concentration, based on one experiment at a single pressure and concentration. The suggested model includes only one fitting parameter, β>1, which takes into account the range of the hydrodynamic influence of a single pore. For a narrow pore size distribution in which one pore diameter predominates (track-etched membranes), the IDE is solved analytically and the derived equation is in good agreement with the measurements on different track-etched membranes. A simple approximate solution of the IDE is derived and that approximate solution, as well as the similarity principal of MF processes, is in good agreement with measurements using a commercial Teflon microfiltration membrane. The theory was further developed to take into account the presence of multiple pores (double, triple and so on pores) on a track-etched membrane surface.

A series of new dead-end filtration experiments are compared with the proposed initial and modified pore blocking models. The challenge suspension used was nearly monodispersed suspension of latex particles of 0.45 μm filtered on a track-etched membrane with similar sized pores 0.4 μm. The filtered suspension concentration ranged from 0.00006 to 0.01% (w/w) and the cross-membrane pressures varied from 1000 to 20,000 Pa. Three stages of microfiltration have been observed. The initial stage is well described by the proposed pore blocking model. The model required only a single parameter that was found to fit all the data under different experimental operational conditions. The second stage corresponds to the transition from the blocking mechanism to the third stage, which is cake filtration. The latter stage occurred after approximately 10–12 particle layers were deposited (mass = 0.006 g) on the surface of the microfiltration membrane.     

Oxovanadium(IV) based coordination polymers and their catalytic potentials for the oxidation of styrene, cyclohexene and trans-stilbene

Reaction between 5,5′-methylenebis(salicylaldehyde) or 5,5′-dithiobis(salicylaldehyde) and 1,2-diaminocyclohexane in equimolar ratio leads to the formation of new polymeric chelating ligands [–CH₂(H₂sal-dach)–]_n (I) and [–S₂(H₂sal-dach)₂–]_n (II). These ligands react with [VO(acac)₂] in DMF to give coordination polymers [–CH₂{VO(sal-dach)·DMF}–]_n (1) and [–S₂{VO(sal-dach)·DMF}–]_n (2). Both complexes are insoluble in common solvents and exhibit a magnetic moment value of 1.74 and 1.78μ_B, respectively. IR spectral studies confirm the coordination of ligands through the azomethine nitrogen and the phenolic oxygen atoms to the vanadium. These complexes exhibit good catalytic activity towards the oxidation of styrene, cyclohexene and trans-stilbene using tert-butylhydroperoxide as an oxidant. Concentration of the oxidant and reaction temperature has been optimised for the maximum oxidation of these substrates. Under the optimised conditions, oxidation of styrene gave a maximum of 76% (with 1) or 85% (with 2) conversion having following products in order of selectivity: benzaldehyde > styreneoxide > 1-phenylethane-1,2-diol > benzoic acid. A maximum of 98% conversion of cyclohexene was obtained with both the catalysts where selectivity of cyclohexeneoxide varied in the order: 2 (62%) > 1 (45%). With the conversion of 33% (with 1) and 47% (with 2), oxidation of trans-stilbene gives benzaldehyde, benzil and trans-stilbeneoxide as major products.     

Efficiency and mechanism of new poly(acryl-phenylamidrazone phenylhydrazide) chelating fiber for adsorbing trace Ga, In, Bi, V and Ti from solution

A new po1y(acrylphenylamidrazone phenylhydrazide) chelating fiber is synthesized from polyacrylonitrile fiber and used for preconcentration and separation of trace Ga(III), In(III), Bi(III), V(V) and Ti(IV) from solution (5–50 ng ml⁻¹ Ti(IV) or V(V) and 50–500 ng ml⁻¹ Ga(III), In (III) or Bi(III) in 1000–100 ml of solution can be enriched quantitatively by 0.15 g of fiber at a 4 ml min⁻¹ flow rate in the pH range 5–7 with recoveries >95%). These ions can be desorbed quantitatively with 20 ml of 4 M hydrochloric acid at 2 ml min⁻¹ from the fiber column. When the fiber which had been treated with concentrated hydrochloric acid and washed with distilled water until neutral was reused eight times, the recoveries of the above ions by enrichment were still >95%. Two-hundred-fold to 10 000-fold excesses of Cu(II), Zn(II), Ca(II), Mn(II), Cr(III), Fe(III), Ba(II) and Al(III) caused little interference in the determination of these ions by inductively coupled plasma-atomic emission spectrometers (ICP-AES). The relative standard deviations for enrichment and determination of 50 ng ml⁻¹ Ga, In or Bi and 10 ng ml⁻¹ V or Ti are in the range 1.2–2.7%. The contents of these ions in real solution samples determined by this method were in agreement with the certified values of the samples with average errors <3.7%.     

Simultaneous recovery of EDTA and lead(II) from their chelated solutions using a cation exchange membrane

Factors affecting the efficiency of electrochemical recovery of EDTA and Pb(II) from their chelated solutions were systematically examined using a cation exchange membrane Neosepta CM-1. The catholyte contained an equimolar amount of Pb(II) and EDTA, and the anolyte contained 0.1 M NaNO₃. The iridium oxide coated on titanium (IrO₂/Ti) and stainless steel were used as anode and cathode, respectively. Experiments were carried out at different current densities (46.3–185 A/m²), initial catholyte pH values (1.47–6.02) and Pb(II) concentrations (0.005–0.03 M). An economically feasible current efficiency and recovery percentages of Pb(II) and EDTA could be achieved if the concentration of the chelated Pb(II) was sufficiently high.     

Preconcentration of copper on ion-selective imprinted polymer microbeads

Molecular recognition-based separation techniques have received much attention in various fields because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the preparation of such systems. In this study, we have prepared a novel molecular imprinted adsorbent to remove heavy metal ions with high selectivity. The Cu(II)-imprinted poly(ethylene glycol dimethacrylate–methacryloylamidohistidine/Cu(II)) (poly(EGDMA–MAH/Cu(II))) microbeads with an average size of 150–200 μm were prepared by dispersion polymerization. These Cu(II) imprinted microbeads were used in the adsorption–desorption of copper(II) ions from metal solutions. Adsorption equilibria was achieved in about 1 h. The maximum adsorption of Cu(II) ions onto imprinted microbeads was about 48 mg/g. The pH significantly affected the adsorption capacity of imprinted microbeads. The observed adsorption order under competitive conditions was Cu(II) > Zn(II) > Ni(II) > Co(II) in mass basis. The imprinted microbeads can be easily regenerated by 0.1 M EDTA solution with higher effectiveness. The imprinted microbeads showed excellent selectivity for the target molecule (i.e. Cu(II) ions due to molecular geometry). These features make imprinted microbeads very good candidate for selective removal of Cu(II) ions at high adsorption capacity. Detection limit was increased at least 1000-folds with the preconcentration approach using the imprinted microbeads. The method was also applied to certified reference and seawater samples.     

Sinterability enhancement in semicokes obtained by controlled pyrolysis of a petroleum residue

Self-sintering semicokes were prepared by pyrolysis of an aromatic petroleum residue at 460–480 °C and pressures of 0.1–1.0 MPa. The evolution of gases and thermoplasticity from resultant semicokes were monitored by TGA and TMA, respectively. Sintering behaviour of the semicokes is extremely sensitive to pyrolysis conditions which determine contents of volatile matter and binder phase. Semicokes produced at 1.0 MPa have high volatile contents with excessive plasticity. Changes of temperature and soak time, used to reduce volatile matter contents induce reductions to the plasticity and sintering. A lower pyrolysis pressure has a similar effect. Although the operational window is narrow, heat-treated compacts (2500 °C) can be made with high density (1.9 g cm⁻³) and bending strengths >75 MPa. Using high-temperature pyrolysis (460 °C) with a post-treatment at 350–400 °C eliminates light components, without decreasing sintering properties. Compacts from these powders also exhibit high density (1.9 g cm⁻³) with higher bending strengths >90 MPa, comparable or superior to mesocarbon microbeads (MCMB) obtained from the same precursor.     

Catalytic effect of zinc oxide on the reduction of barium sulfate by methane

Reduction of barium sulfate by methane was investigated in this work. The thermogravimetric method was used to obtain kinetic parameters of the reaction in the temperature range of 900–975 °C at atmospheric pressure. The kinetics of the reaction has been studied both in the absence and presence of zinc oxide as a catalyst. The conversion–time data have been interpreted by using the grain model, and the effect of catalyst on the kinetic parameters has been elucidated. It was found that zinc oxide acted as fairly strong catalyst for the reaction, especially at higher temperatures. At about 975 °C the reaction rate constant was increased more than 7 times by using 2% of zinc oxide. This enhancement in the rate constant is valuable for industries.     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

Chemistry and reactivity of dinuclear manganese oxamate complexes: Aerobic catechol oxidation catalyzed by high-valent bis(oxo)-bridged dimanganese(IV) complexes with a homologous series of binucleating 4,5-disubstituted-o-phenylenedioxamate ligands

The high-valent bis(oxo)-bridged dimanganese(IV) complexes with the series of binucleating 4,5-X₂-o-phenylenebis(oxamate) ligands (opbaX₂; X = H, Cl, Me) (1a–c) have been synthesized and characterized structurally, spectroscopically and magnetically. Complexes 1a–c possess unique Mn₂(μ-O)₂ core structures with two o-phenylenediamidate type additional bridges which lead to exceptionally short Mn–Mn distances (2.63–2.65 Å) and fairly bent Mn–O–Mn angles (94.1°–94.6°). The cyclovoltammograms of 1a–c in acetonitrile (25 °C, 0.1 M Bu₄NPF₆) show an irreversible one-electron oxidation peak at moderately high anodic potentials (E_ap = 0.50–0.85 V versus SCE), while no reductions are observed in the potential range studied (down to −2.0 V versus SCE). These dinuclear manganese oxamate complexes are excellent catalysts for the aerobic oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone in acetonitrile at 25 °C. The order of increasing catecholase activity (k_obs) with the electron donor character of the ligand substituents as 1b (X = Cl) < 1a (X = H) < 1c (X = Me) correlates with Hammett σ⁺ values (ρ = −0.95). A mechanism involving initial activation of the catechol substrate by coordination to the dimetal center and subsequent oxidation to quinone by O₂ is proposed, which is consistent with the observed saturation kinetics.     

Co-aggregation of fullerene C60 and thiophene in the non-aromatic solvent cyclohexene

Co-aggregation of fullerene C₆₀ and thiophene has been studied calorimetrically in cyclohexene at 25 °C. The total aggregation heat is found to depend on initial concentration of thiophene and fall between −1.9 and −5.8 kJ mol⁻¹. The corresponding thiophene/fullerene molar ratio (“co-aggregation number”) ranges from 7 to 12. The data are rationalized by formation of heteromolecular nanoaggregates with intermolecular contacts of both fullerene–thiophene and fullerene–fullerene types. A physical model describing interaction between fullerenes and π-donors in solution is substantiated and used to explain heterogeneity of composites containing fullerenes.     

Poly(styrene-co-acrylonitrile) based proton conductive membranes

Sulfonated poly(styrene-co-acrylonitrile) (PSAN–SO₃H) membranes were obtained by sulfonation of the original styrene–acrylonitrile copolymer, in different molar ratios, and characterized by vibrational spectroscopy (FTIR), thermal analyses (TGA and DSC) and electrochemical impedance spectroscopy (EIS). The thermal stability of the sulfonated polymers exhibited a dependence on the sulfonation degree and reached 261 °C for samples up to 1:4 (sulfonating agent to styrene unit). FTIR spectra showed the covalent incorporation of sulfonic groups at the styrene units, confirming the PSAN–SO₃H formation. Vibrational spectra also indicated the presence of hydronium ions and dissociated sulfonic groups, indicating the existence of mobile protons for ion conduction. DSC analyses evidenced two glass transition temperatures (T_g), one associated with an ion-water domain and other with the chain backbone glass transition. The maximum conductivity of PSAN–SO₃H membranes at ambient temperature was about 10⁻³ Ω⁻¹ cm⁻¹, achieving 10⁻² Ω⁻¹ cm⁻¹ at 80 °C. The conductivity dependency on the temperature was found to be linear, similarly to other sulfonic acid polymers described on the literature, and the water uptake reaches 45.7% of the polymer mass, against 18.9% of the original copolymer.     

Non-isothermal thermoanalytical studies on the salt roasting of chalcopyrite using KCl

In an earlier study [1], the isothermal kinetics of salt roasting of chalcopyrite under an oxidizing atmosphere using KCl was studied in the temperature range 523–773 K. The salt roasting reaction was found to be chemically controlled at temperatures below 600 K both under static air and oxygen atmosphere. At higher temperatures, the process was not thermally activated because of a change in the chemistry of the process. In the present study, the salt roasting of chalcopyrite using KCl under oxygen and static air atmosphere was studied by non-isothermal thermoanalytical studies up to 723 K. The effect of salt content, heating rate and particle size on the salt roasting behavior was studied using TG/DTA techniques at a programmed linear heating rate. The TG and DTA studies reveal two distinct chemical processes, one operative up to 620 K and the other from 620 to 723 K. The integral method of Coats and Redfern was used for the treatment of non-isothermal kinetic data. The non-isothermal analysis confirmed the chemical control mechanism at temperatures below 620 K. However, the activation energy for the process derived from non-isothermal thermogravimetric analysis is almost twice as that deduced from isothermal measurements. In the temperature range 620–723 K, the kinetic data still obeys the interfacial reaction control model although the activation energy in this temperature range is very low.     

Pt-induced faceting of W field emitter tips

Changes in surface morphology that accompany the adsorption of Pt on W are studied using field emission microscopy. During the adsorption of Pt at coverages of >1 monolayer (ML) at 800–1400 K, the shape of a W microcrystal tip is changed from nearly hemispherical to a more polyhedral form. This transition is connected with faceting of the substrate, which is manifested by changes in size and in electron emission of planes mainly along the 1 1 1 zones, e.g., {2 1 1}, {3 2 1}, {8 7 1}. The sizes of (  1 2) and (  2 3) facets are determined along and perpendicular to the [1   1] directions during adsorption up to an average Pt coverage 3.5 ML. The biggest increase of surface area is observed for {2 1 1} facets at 1400 K, which implies that the surface free energy γ₁₁₂ is considerably reduced relative to the average surface free energy. The results are compared with data for other bimetallic systems, and are discussed in terms of the anisotropy of surface free energy, the equilibrium crystal shape (ECS) and the steady-state tip shape (SSTS). There are quantitative differences found between the SSTS and the ECS for Pt/W.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Effect of pH on the characteristics of potassium permanganate–luminol CL reaction in the presence of trace aluminum(III) and its analytical application

At pHs ≥ 11.45, trace Al was found to enhance the CL from luminol–KMnO₄ system. However, at pHs ≤ 10.42, it was found to inhibit strongly the CL from luminol–KMnO₄ system. The effect of pH, luminol and potassium permanganate concentrations on the kinetic characteristics of CL system was investigated in the presence of trace Al. On this basis, a flow injection inhibition chemiluminescence method was established for the determination of trace Al in this study. Under optimized conditions, the CL decreased linearly with Al(III) concentration in the range of 8–500 μg L⁻¹ and the detection limit (3σ) of 2 μg L⁻¹. The relative standard deviation (R.S.D.) is 3.6% for 100 μg L⁻¹ Al(III) (n = 11). The method has been applied to the determination of trace Al in real water samples with satisfactory results without the pretreatment of samples. The results given by the proposed method are in good agreement with those given by ICP-AES detection method.     

Colloidal crystals of core-shell type spheres with poly(styrene) core and poly(ethylene oxide) shell

Elastic modulus and crystal growth kinetics have been studied for colloidal crystals of core–shell type colloidal spheres (diameter = 160–200 nm) in aqueous suspension. Crystallization properties of three kinds of spheres, which have poly(styrene) core and poly(ethylene oxide) shell with different oxyethylene chain length (n = 50, 80 and 150), were examined by reflection spectroscopy. The suspensions were deionized exhaustively for more than 1 year using mixed bed of ion-exchange resins. The rigidities of the crystals range from 0.11 to 120 Pa and from 0.56 to 76 Pa for the spheres of n = 50 and 80, respectively, and increase sharply as the sphere volume fraction increase. The g factor, parameter for crystal stability, range from 0.029 to 0.13 and from 0.040 to 0.11 for the spheres of n = 50 and 80, respectively. These g values indicate the formation of stable crystals, and the values were decreased as the sphere volume fraction increased. Two components of crystal growth rate coefficients, fast and slow, were observed in the order from 10⁻³ to 10¹ s⁻¹. This is due to the secondary process in the colloidal crystallization mechanism, corresponding to reorientation from metastable crystals formed in the primary process and/or Ostwald-ripening process. There are no distinct differences in the structural, kinetic and elastic properties among the colloidal crystals of the different core–shell size spheres, nor difference between those of core–shell spheres and silica or poly(styrene) spheres. The results are very reasonably interpreted by the fact that colloidal crystals are formed in a closed container owing to long-range repulsive forces and the Brownian movement of colloidal spheres surrounded by extended electrical double layers, and their formation is not influenced by the rigidity and internal structure of the spheres.     

Kinetics of the Hydrogenation of Pinane Hydroperoxide to Pinanol on Pd/C

The liquid-phase hydrogenation of pinane hydroperoxide (PHP) to pinanol on a Pd/C catalyst at 20–80°C and hydrogen pressures of 1–11 atm was studied. It was found that the rate of hydrogenation decreased with PHP concentration. The rate of PHP hydrogenation dramatically increased as the pressure of hydrogen was increased in a range of 2.5–3 atm. A mechanism was proposed for the hydrogenation of PHP. According to this mechanism, the step of hydrogen activation (homolytic or heterolytic addition) depends on the redox properties of the catalyst surface (the ratio between adsorbed PHP species and H₂). It was found that pinanol can be prepared with high selectivity by the hydrogenation of PHP on a Pd/C catalyst under mild conditions.     

Methoxycarbonylation of propylene oxide: A new way to β-hydroxybutyrate

The methoxycarbonylation of propylene oxide (PO) to methyl β-hydroxybutyrate (MHB) catalyzed by dicobaltoctacarbonyl ([Co₂(CO)₈]) and 3-hydroxypyridine (3-OH-Py) in methanol system has been studied. The effects of different additives, the molar ratio of 3-OH-Py:Co₂(CO)₈, temperature, carbon monoxide (CO) pressure, reaction time on the conversion and selectivity have been investigated. The conversion of propylene oxide is 80.4%, and the yield of methyl β-hydroxybutyrate is 74.9% with selectivity 93.2% when the reaction is carried out for 16 h at 80 °C and 6.0 MPa of CO in methanol, with 0.125 mmol of Co₂(CO)₈, 0.25 mmol of 3-OH-Py. The mechanism of this catalytic reaction has also been proposed.