Anodic Oxidation of Unsaturated Aliphatic Ethers in aqueous electrolytes

2,5-dihydrofuran 1 was galvanostatically oxidized in aqueous electrolytes on Pt and PbO₂ anodes at current densities of 10 to 50 mA cm⁻². Under acidic conditions maleic dialdehyde 2 was obtained on both electrodes with a current efficiency (c.e) of up to 50%. In the alkaline region (pH 10) 4-hydroxy crotonic aldehyde 3 (Pt) or 2,5-dihydrofuranone 4 (PbO₂) become the main products with c.e.'s of 29% and 27%, respectively, depending on the anode material. The influence of pH and of the anode material are discussed in detail. 2,3-dihydrofuran 7 , vinyl ethyl ether 8 and for comparison, furan 9 were studied in addition.     

Catalyst-Controlled Selectivity in Oxidation of Olefins: Highly Facile Success to Functionalized Aldehydes and Ketones

Catalysis Letters - The attractive challenge in green chemistry is exploring novel heterogeneous catalyst system for catalyst-controlled product selectivity for oxidation of olefins. Hence, we...     

Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

The photodynamics of acetone and some other simple aliphatic ketones in the nπ* state are discussed in the light of recent results obtained in seeded supersonic beams. The Born-Oppenheimer approximation is used to describe the sequence of events beginning with light absorption and ending in molecular fragmentation. Intersystem crossing is shown to be an important process even for the isolated molecule. Its rate increases with the internal energy and may be related to the density of states in the triplet state. For all molecules studied so far, the results can be rationalized by assuming that dissociation takes place on the triplet surface, the S₁ surface being stable in the energy range pertinent to these experiments (up to 35,000 cm⁻¹ above the ground state). Fluorescence spectroscopy may be used also to detect small clusters. In the case of acetone, their presence is indicated by the decrease in the intensity of some spectral lines as a function of cooling efficiency. The results are used to estimate an upper limit for the van der Waals binding energies.     

Study of Catalyst Selectivity in the Oxidation of Phenol

The selectivity of -crystalline zirconium phosphate, amorphous zirconium phenylphosphonate, amorphous zirconium molybdenum phosphate and microporous crystalline aluminium methylphosphonate was evaluated in oxidation reactions of phenol. The different selectivities are correlated to the properties and structure of each compound.     

The Partial Anodic Oxidation of Aliphatic Hydrocarbons

The types of electrode processes which result in the functionalisation of aliphatic hydrocarbons are discussed and some recent results on the partial anodic oxidation of aliphatic hydrocarbons in aprotic media and in fluorosulphonic acid are presented.     

The oxidation of aqueous ferrous sulphate by thiobacillus ferrooxidans

The iron oxidizing bacteria, Thiobacillus ferrooxidans, were grown in an aqueous ferrous sulphate solution in batch and continuous culture vessels and the dependency of the specific growth rate on ferrous sulphate concentration, temperature, and pH are shown. The effect of carbon dioxide concentration on cell growth is also considered. The phenomenon of wall-growth is shown to be an important characteristic of the organism which must be considered in any batch or continuous culture experiments. The role that it may have in the biological leaching process is also indicated.     

Recovery of copper from sulphate medium by Lix-84 in kerosene

The extraction–stripping reaction of Cu(II) by Lix-84 in kerosene from aqueous sulphate medium of pH 2·5 has been investigated. The effects of pH, metal ion, extractant and strip solution concentrations as well as the loading capacity of the extractant were investigated. The number of stages required for the extraction and stripping of copper was also evaluated. The results are used to assess the conditions for purification of industrial waste solutions containing copper through counter-current extraction in a horizontal mixer-settler.     

Oxidation of ferrous sulphate in presence of sodium carbonate

Isothermal oxidation of ferrous sulphate heptahydrate in presence and absence of sodium carbonate has been carried out in the temperature range 205 to 265 °C. The oxidation proceeds in two steps. The rate constants for the oxidation at various temperatures have been calculated. The results indicate that the low temperature mechanism of oxidation proposed earlier does not hold good at higher temperatures.     

Some aspects of the behaviour of potassium sulphate in aqueous solutions

The solubility of potassium sulphate in sulphuric acid at 293°K has been determined. The effects of traces of Fe²⁺, Fe³⁺ and Cr³⁺ ions on the recrystallisation of potassium sulphate from both neutral and acidic solutions have been studied. While Fe²⁺ ions had no significant effect, concentrations of 0.07 g Fe³⁺ or 0.02 g Cr²⁺ per 100 g H₂O inhibited crystallisation of potassium sulphate from 100% supersaturated solutions. A method for purifying potassium sulphate contaminated with Fe³⁺ and Cr³⁺ ions, by means of fractional crystallisation, is outlined.     

The Protein Environment Drives Selectivity for Sulfide Oxidation by an Artificial Metalloenzyme

Magic Mn–salen metallozyme : The design of an original, artificial, inorganic, complex‐protein adduct, has led to a better understanding of the synergistic effects of both partners. The exclusive formation of sulfoxides by the hybrid biocatalyst, as opposed to sulfone in the case of the free inorganic complex, highlights the modulating role of the inorganic‐complex‐binding site in the protein.

     

The diffusion coefficient of copper sulphate in aqueous solution

The diffusion coefficient, D, of CuSO₄ in aqueous solution was determined at 298.1 K by chronopotentiometry and also with a rotating disc electrode using the mixed control Levich equation. For 0 < [CuSO₄] < 0.05 mol dm^?3, D = {7.35 ± 0.18 ? (5.3 ± 1.4) [CuSO₄]^{$\text{1}\text{2}$}} × 10^?10 m² s^?1, at a constant ionic strength of 1.58 mol dm^?3 maintained with either H₂SO₄ or Na₂SO₄ (pH = 2). It was shown that substantial variations in the concentration of the supporting electrolyte had negligible effect on the above values of D. It was found that literature values of D vary over a three-fold range, even when corrected to the same temperature and CuSO₄ concentration. Much of this variation probably arises from rotating disc determinations carried out at disc potentials where activation control is significant. This problem is overcome if the mixed control Levich equation is used to treat the data instead of the commonly used simple (diffusion only) Levich equation.     

Cadmium removal from aqueous sulphate solutions by treatment with iron felts

The possibility of removing cadmium from effluents byelectrochemical treatment using iron felts as three-dimensional electrodes was investigated. It was found that iron felts remove cadmium by three paths: (i) adsorption of cadmium ions by hydrous ferric oxide, (ii) cathodic electrodeposition and (iii) precipitation of cadmium hydroxide due to the localized alkalinity produced by the hydrogen evolution. The adsorption isotherm, at 30°C, of cadmium ions from an aqueous sulphate solution on hydrous ferric oxide is given. The influence of cathodic potential, volumetric flow rate and interelectrode gap on the current, current efficiency and fractional conversion is discussed. The iron felts proved to be efficient in removing cadmium. The highest fractional conversion, ≌25% for single pass operation, with 100% current efficiency was obtained for a volumetric flow rate of 9·57×10⁻⁶ m³ s⁻¹ using iron felt cathodes of 4×10⁻³ m thickness potentiostated at potentials lower than −1·5 V against a saturated calomel electrode. © 1998 Society of Chemical Industry     

Free radicals formation induced by the ozonation of humic substances in aqueous medium

This laboratory study was designed to investigate the mechanism of the formation of the OH radicals during the ozonation of humic substances solutions. The evaluation of the formation of these radical species was performed by using 1,1,2-trichloro ethane (TCA) as a probe. The apparent removal of TCA observed during the ozonation treatment implies the production of secondary species that catalyze the generation of OH radicals from ozone. These species are formed by a reaction between H₂O₂, formed in-situ, and O₂ and by a radical mechanism involving reactive humic substances sites.     

Multicomponent Oxides in Selective Oxidation of Alkanes Theoretical Acidity versus Selectivity

Semi-empirical relationships between the ‘optical basicity’ Λ (so-called after Duffy) of solid oxides and the ‘thermodynamic’ selectivity in mild and total oxidation of hydrocarbons have recently been set up. They can be used to determine the optimum acidity of a solid catalyst or to account for its observed selectivity in a given reaction. The oxidic M_xO_z catalysts were ranked by means of the electron-donor power of oxygen which is represented by the optical basicity Λ. The difference of ionization potential I of molecules when the reactant becomes the product, which represents the variation of electron-donor power during the reaction, was used to rank reactions. Plotting ΔI against Λ for each ‘reaction/selective catalyst’ couple results in straight lines, the equation of which depends on the chemical nature of reactant (alkane and alkyl-aromatics, alkenes and aromatics, alcohols) and on the deepness of oxidation (ammoxidation, mild oxidation, total oxidation). The correlations are used to discuss the behaviour of V- and Mo-based, simple and multicomponent oxide catalysts, in the mild oxidation of C₂ and C₃ hydrocarbons.     

Partial Oxidation of Methane Over Co-ZSM-5: Tuning the Oxygenate Selectivity by Altering the Preparation Route

For the first time the possibility to partially oxidize methane to methanol and formaldehyde at low temperature over Co-ZSM-5 using air is shown. The influence of the preparation method on the nature of the cobalt species is investigated. In addition, the catalytic activity and selectivity for methane oxidation as a function of the cobalt speciation is discussed. Based on UV–vis–NIR and FT-IR spectroscopy, H₂-TPR, TEM and kinetic measurements it is concluded that cobalt in ion-exchange positions results mainly in the formation of formaldehyde, while larger Co-oxide particles prepared by impregnation result in the formation of methanol.     

Kinetics of copper dissolution and deposition in aqueous sulphate solution

Galvanostatic single-pulse, rotating-disc and chronopotentiometric measurements on etched polycrystalline copper electrodes in semimolar mixed solutions of CuSO₄, MgSO₄ and H₂SO₄ at 25°C have yielded kinetic parameters and specific rate data for either of the two consecutive charge-transfer steps of the Cu(I)/Cu(II) electrode. The ion-transfer step Cu/Cu(I), but not the electron-transfer step Cu/Cu(II), depends on a surface factor for crystal growth and demolition. Some information on this factor is obtained. Comparisons are made to the solid Ni/Ni(II) electrode and to the liquid Cu(Hg)/Cu(II) electrode.     

Selectivity in gas purification: film theory,semi-infinite medium

A film theory model describing simultaneous transport of two gases into a reactive liquid has been used in an examination of the conditions that optimize selectivity. One component reacts instantaneously, the other at a finite rate. The resulting unstable two point boundary value problem was solved numerically for a range of the dimensionless numbers that characterize an important application for this system. Selectivity is shown to be favored by low interfacial concentrations of both gases but particularly of the component reacting instantaneously; it is also favored by high concentrations of the non-volatile liquid reactant. Selectivity can be high while the rate of transfer of the selective component can also be large. Good mixing can further help the selectivity if this does not significantly reduce the bulk concentrations of the non-volatile reactant. A boundary condition of the film theory often imposed on such systems is shown to be unnecessary.     

Oxidation of organic pollutants in aqueous solutions by nanosized copper oxide catalysts

The catalytic activity of copper oxide nanoparticles was investigated for the removal of organic pollutants in aqueous solutions, using hydrogen peroxide as an oxidant. Complete degradation of both alachlor and phenanthrene was achieved after 20 min. The kinetics of the reaction was found to be pseudo-first-order with respect to the pollutant. The influence on the reaction kinetics of different catalyst samples, consisting of the same material but of different origin and different particle properties, was examined. The effects of several factors such as irradiation, oxidant concentration, ionic strength and pH on the reaction were also investigated. The catalysis is not photo-induced and can be performed without UV–vis irradiation. In particular, an optimal oxidant concentration was determined for the studied system. The presence of salts was found to inhibit the alachlor degradation rate. The addition of high concentrations of oxidant or salt results in pseudo-zero-order kinetics. However, NaCl at very high concentrations (>1 M) was found to cause a dramatic increase in reaction rate. The catalysis is efficient over a wide range of pH values.     

Regeneration of spent earth in aqueous medium

A simple method of regeneration of spent earth at a relatively low temperature has been developed. Deoiled spent earth was regenerated in the form of a slurry using water as an aqueous phase, in the temperature range of 170–270°C. The effects of temperature, slurry concentration and cycle of regeneration have been studied. An attempt has been made to discern the controlling mechanism. Regenerated earth from the present method does not impart any malodor to the oil as against theramlly regenerated earth.     

Conductimetric studies of chitosan in aqueous medium

Summary Conductimetric studies of two aqueous chitosan salts systems are presented. These salts were prepared dissolving the polyelectrolyte with desionised water and using an excess of the corresponding stoichiometric amount of acid (HCl or HNO₃) and then purified by dialysis. Limit equivalent conductance (Λ^o) was obtained by fitting the experimental conductimetric results to a fifth order polynomial function. This result was employed to determine classical conductimetric parameters in dilution limiting conditions, i.e., charge parameter (ξ), polyelectrolyte equivalent ionic conductivity (λ_p^o), fractional hydrodynamic coefficient (f), etc., employing Kohlrausch law for independent ions migration. We have found a remarkable agreement between experimental and theoretical results when Rinaudo equation was employed to calculate ξ. Additionally, our conductimetric studies show that equilibrium constants are similar for both systems when K values are obtained from plots of Λ²/[Λ^o(Λ^o-Λ)] vs. 1/c_p.