Oxidation of substituted benzylic hydrocarbons and naphthalenes by peroxydisulphate in the presence of metal ions

Oxidations of various substituted benzylic hydrocarbons with peroxydisulphate in the presence of metal ion catalysts like iron, nickel, copper, cobalt, silver and cerium were examined. Among the metal ions copper (II) catalysed reaction gives products in excellent yield, whereas oxidation of naphthalene and substituted naphthalenes gives low to moderate yield of the products with peroxydisulphate- copper (II).

Oxidation of Sulfur Dioxide in Aqueous Suspensions of Activated Carbon

Sulfur dioxide in aqueous solutions at low pH levels exists both in molecular SO2(aq) and in hydrolyzed ionic form HSO3-. Experiments indicate that only HSO3- is the reacting species in the oxidation catalyzed by activated carbon, while SO2(aq) deactivates by competing with HSO3 for the active sites of the catalyst particles. A mechanism is proposed and a rate model is developed that also accounts for the effect of sulfuric acid (product of the oxidation) on the solubility of sulfur dioxide. It predicts first order in HSO3-, half order in dissolved oxygen, and a linear deactivation effect of SO2(aq), which are confirmed by experimental data. The deactivation reaches a constant level corresponding to saturation of the active sites by SO2(aq). Activation energy for the oxidation is 93.55 kJ mol(-1) and for deactivation is 21.4 kJ mol(-1).

Reactions of cyanogen radical with alkanes and an explanation for negative temperature dependence of rate constants

Reactions of cyanide radicals with alkanes have been investigated by ab initio methods. It is found that the potential energy surface for reaction of CN with a primary C-H bond in methane has a small positive barrier while reactions of CN with a secondary and a tertiary C-H bond in alkanes are barrierless at the correlated level. A simple explanation for the obtained negative temperature dependence of rate constants for reactions of CN with a secondary and a tertiary C-H bond in alkanes are given in terms of the collision theory of bimolecular reactions. It is shown that for barrierless reactions the negative temperature dependence of the rate constants is attributed to the variation of the pre-exponential factor with temperature.

Synthesis, structure and properties of monomeric complexes obtained from the cleavage of a (?-oxo)bis(?-carboxylato) diruthenium(III) core

Reaction of [Ru2O(O(2)CR)(2)(MeCN)(4)(PPh(3))(2)](ClO4)(2) (1) with 1,2-diaminoethane (en) in MeOH-H2O yielded a mixture of products from which a diamagnetic ruthenium(II) complex [Ru(MeCN)(en)(2)(PPh(3))](ClO4)(2) (2) and a paramagnetic ruthenium(III) species [Ru(O(2)CR)(en)(2)(PPh(3))](BPh(4))(2) (3) (R = Ph, a; C6H4-p-Me, b; C6H4-p-OMe, c) were isolated and characterized. The crystal structure of complex 2, obtained by X-ray diffraction analysis, shows a cis arrangement of the unidentate ligands in this octahedral complex. Complex 3 displays an axial EPR spectrum. Complex 2 undergoes two successive irreversible metal-centred one-electron oxidation processes at 1.13 and 1.33 V vs SCE in MeCN-0.1 M [NBu(4)(n)]ClO4 at 50 mV s(-1). The mechanistic aspects of the core cleavage reactions in 1 are discussed.

Mutations in the Res subunit of the EcoPI restriction enzyme that affect ATP-dependent reactions

The Res subunits of the type III restriction-modification enzymes share a statistically significant amino acid sequence similarity with several RNA and DNA helicases of the so-called DEAD family. It was postulated that in type III restriction enzymes a DNA helicase activity may be required for local unwinding at the cleavage site. The members of this family share seven conserved motifs, all of which are found in the Res subunit of the type III restriction enzymes. To determine the contribution, if any, of these motifs in DNA cleavage by EcoPI, a type III restriction enzyme, we have made changes in motifs I and II. While mutations in motif I (GTGKT) clearly affected ATP hydrolysis and resulted in loss of DNA cleavage activity, mutation in motif II (DEPH) significantly decreased ATP hydrolysis but had no effect on DNA cleavage. The double mutant R.EcoPIK90R-H229K showed no significant ATPase or DNA restriction activity though ATP binding was not affected. These results imply that there are at least two ATPase reaction centres in EcoPI restriction enzyme. Motif I appears to be involved in coupling DNA restriction to ATP hydrolysis. Our results indicate that EcoPI restriction enzyme does not have a strand separation activity. We suggest that these motifs play a role in the ATP-dependent translocation that has been proposed to occur in the type III restriction enzymes. (C) 1997 Academic Press Limited.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

Oxidation of methanol on the surfaces of model Cu/ZnO catalysts containing Cu1+ and Cu-0 species

Interaction of CH3OH with Cu clusters deposited on ZnO films grown on a Zn foil as well as on a ZnO(0001)Zn crystal, has been examined by X-ray photoelectron spectroscopy. On clean Cu clusters, reversible molecular adsorption or formation of CH3O is observed. However if the Cu clusters are pretreated with oxygen, both CH3O and HCOO- species are produced. Model Cu/ZnO catalyst surfaces, containing both Cu1+ and Cu-0 species, show interesting oxidation properties. On a Cu-0-rich catalyst surface, only CH3O species is formed on interaction with CH3OH. On a Cu1+-rich surface, however, HCOO- ion is the predominant species.

Sulfur transfer reactions of tetrathiomolybdate in water: Synthesis of alkyl disulfides from alkyl halides

Reaction of a number of alkyl halides with tetrathiomolybdate in water as the solvent affords the corresponding disulfides in good yields.

Ultrafast Microwave-Assisted Route to Surfactant-Free Ultrafine Pt Nanoparticles on Graphene: Synergistic Co-reduction Mechanism and High Catalytic Activity

We demonstrate an ultrafast method for the formation of, graphene supported Pt catalysts by the co-reduction of graphene oxide and Pt salt using ethylene glycol under microwave irradiation conditions. Detailed analysis of the mechanism of formation of the hybrids indicates a synergistic co-reduction mechanism whereby the presence of the Pt ions leads to a faster reduction of GO and the presence of the defect sites on the reduced GO serves as anchor points for the heterogeneous nucleation of Pt. The resulting hybrid consists of ultrafine nanoparticles of Pt uniformly distributed on the reduced GO susbtrate. We have shown that the hybrid exhibits good catalytic activity for methanol oxidation and hydrogen conversion reactions. The mechanism is general and applicable for the synthesis of other multifunctional hybrids based on graphene.

Molecular structure and reactions of 1,1 '-bi(acenaphthen-1-ylidene)-2,2 '-dione

The molecular structure of 1,1'-bi(acenaphthen-1-ylidene)-2,2'-dione 1, a potential building-block for the synthesis of fullerene fragments, has been investigated by X-ray crystallography and semi-empirical (AM1 and PM3) calculations. There is a good agreement between the calculated and crystal structure which is essentially planar and has E-configuration. In the solid state, molecules of 1 pack in an interesting manner as corrugated sheets sustained by a network of C-H ... O hydrogen bonds and resulting in the formation of tetrameric loops. While steric factors limit the reactivity of the carbonyl groups in 1, the ene double bond of the ene-dione moiety present in it exhibits propensity toward [4 + 2]-cycloadditions to furnish novel and highly compressed polycycles 8-10.

Characterization and catalytic properties of combustion synthesized Au/CeO2 catalyst

Ceria-supported Au catalyst has been synthesized by the solution combustion method for the first time and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Au is dispersed as Au as well as Au3+ states on CeO2 surface of 20-30 nm crystallites. On heating the as-prepared 1% Au/CeO2 in air, the concentration of Au3- ions on CeO2 increases at the expense of Au. Catalytic activities for CO and hydrocarbon oxidation and NO reduction over the as-prepared and the heat-treated 1% Au/CeO2 have been carried out using a temperature-programmed reaction technique in a packed bed tubular reactor. The results are compared with nano-sized Au metal particles dispersed on alpha-Al2O3 substrate prepared by the same method. All the reactions over heat-treated Au/CeO2 occur at lower temperature in comparison with the as-prepared Au/CeO2 and Au/Al2O3. The rate of NO + CO reaction over as-prepared and heat-treated 1% Au/CeO2 are 28.3 and 54.0 mumol g(-1) s(-1) at 250 and 300 degreesC respeceively. Activation energy (E,) values are 106 and 90 kJ mol(-1) for CO + O-2 reaction respectively over as-prepared and heat-treated 1% Au/CeO2 respectively.

Chiral Mitsunobu reactions with (1S)-(+)-ketopinic acid: kinetic resolutions of secondary alcohols

Several secondary alcohols undergo the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and (1S)-(+)-ketopinic acid (0.5 equiv. each relative to alcohol) in CH2Cl2 solution at -23degreesC, to furnish the chiral secondary alcohol and its ketopinate ester (d.e. >95%,). Chromatographic separation of these and subsequent hydrolysis of the ketopinate ester (KOH EtOH/0degreesC) provides the chiral secondary alcohol in overall yields of similar to75% and e.e. of similar to80%. When the above Mitsunobu reaction is performed with 1 equiv. of all the reactants. an effective dynamic kinetic resolution of the alcohol is observed in two cases, the ketopinate esters being isolated in 63 and 75% yields and >95% d.e. (C) 2002 Elsevier Science Ltd. All rights reserved.

Electrochemical co-deposition of bimetallic Pt-Ru nanoclusters dispersed on poly(3,4-ethylenedioxythiophene) and electrocatalytic behavior for methanol oxidation

Nanoclusters of bimetallic Pt-Ru are electrochemically deposited on conductive polymer, poly(3,4-ethylenedioxythiophene)(PEDOT), which is also electrochemically deposited on a carbon paper substrate. The bimetallic deposition is carried out in an acidic electrolyte consisting of chloroplatinic acid and ruthenium chloride at 0.0 V versus saturated calomel electrode (SCE) on PEDOT coated carbon paper. A thin layer PEDOT on a carbon paper substrate facilitates the formation of uniform, well-dispersed, nano clusters of Pt-Ru of mean diameter of 123 nm, which consist of nanosize particles. In the absence of PEDOT, the size of the clusters is about 251 nm, which are unevenly distributed on carbon paper substrate. Cyclic voltammetry studies suggest that peak currents of methanol oxidation are several times greater on PtRu-PEDOT electrode than on Pt-Ru electrode in the absence of PEDOT. (C) 2011 Elsevier B.V. All rights reserved.

Electrochemically deposited crystalline thin film of polyaniline on nickel for redox reactions at positive potentials

Redox reactions which occur at positive potentials such as ferrous/ferric, hydroquinone/quinone, ferrocyanide/ferricyanide etc. in aqueous acidic electrolytes cannot be studied on non-platinum metals, for example, a Ni electrode. On the contrary, these reactions occur on polyaniline (PANI) modified Ni electrodes, as evidenced from cyclic voltammetry, amperometry and steady-state polarization experiments. Under identical experimental conditions of scan rate (v) and concentration (C), the peak current density (i(p)) values of Fe2+/Fe3+ redox reaction are greater on the PANI modified Ni than on Pt. Additionally, the peak potential separation (DeltaE(p)) of the voltammogram is lesser on the PANI modified Ni. With an increase in thickness of the PANI, DeltaE(p) increases suggesting that the redox reactions tend to depart from the reversibility. Scanning electron micrographs reveal the presence of a crystalline deposit of PANI on Ni when the thickness of PANI is about 0.08 mum. However, the PANI becomes amorphous and porous at higher thickness values. Raman spectroscopy and X-ray diffraction studies corroborate the observations made out of scanning electron microscopy. Higher catalytic activity of PANI is attributed to crystalline nature of PANI on Ni. Exchange current density and standard rate constant of Fe2+/Fe(3+)redox reaction are evaluated. (C) 2002 Published by Elsevier Science B.V.