Synthesis of ROMP Monomers Containing Metal–Metal Bonds

Methods for the synthesis of cyclic monomers that have both metal–metal bonds and carbon–carbon double bonds are reported. Ring opening metathesis polymerization (ROMP) of these monomers would yield polymers that are photochemically degradable. The first method investigated involved substitution of Cp₂Fe₂(CO)₄ by the bidentate phosphine ligand DPPEN (Ph₂P CH=CH–PPh₂). Cp₂Fe₂(CO)₂( -DPPEN) was synthesized and the X-ray crystal structure is reported but the molecule could not be polymerized by a ROMP method using Grubbs’s catalyst. The inability of this monomer to polymerize (or copolymerize with cyclooctatetraene) was attributed to the bulky phenyl rings being in close proximity to the C=C in the DPPEN ligand, which prevents coordination of the monomer to the catalyst. To decrease the steric interactions, the DPPBN ligand was synthesized (DPPBN=Ph CH CH=CH CH PPh₂). However, the reaction of DPPBN with Cp₂Fe₂(CO)₄ yielded the product Cp₂Fe₂(CO)₂( -1,2,4-triphos), where the 1,2,4-triphos ligand is a tridentate ligand formed by the formal additional of Ph₂PH to DPPBN (1,2,4-triphos=Ph CH CH(PPh₂) CH CH PPh₂). An X-ray structure of the Cp₂Fe₂(CO)₂( -1,2,4-triphos) complex revealed that the 1,2,4-triphos ligand chelates exclusively through the two phosphorus atoms that are bridged by two carbon atoms. It is suggested that this structural feature may simply reflect the increased stability of the 6-membered ring over the 7- and 8-membered rings. The reactions of the Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ dimers with DPPBN were investigated next. Reactions of Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ with the DPPEN and DPPBN ligands resulted in the disproportionation of the dimers. The X-ray crystal structure of [CpMo(CO)₂(DPPEN)][CpMo(CO)₃] was determined and is reported. The CpMo(CO)(DPPEN)Cl complex was formed when these same reactions were carried out in the presence of CH₂Cl₂. The X-ray crystal structure of this molecule is also reported.     

Synthesis and Polymerization of Cationic bis(cyclopentadienyliron)arene Complexes Containing Arylazo Dyes

The synthesis of the title complexes was achieved via the reaction of -p-dichlorobenzene- -cyclopentadienyliron cations with 4,4′-bis(4-hydroxyphenyl)valeric acid to produce the diiron complexes which were then reacted with a number of arylazo dyes to give cationic bis(cyclopentadienyliron)arene complexes containing the arylazo dyes. These iron-containing monomers were subsequently polymerized via nucleophilic aromatic substitution using 1,8-octanedithiol, 4,4′-thiobisbenzenethiol, or bisphenol A to produce the desired coloured cationic organoiron polymers. The weight – average molecular weights were estimated to range from 11,800 to 31,600. UV–vis studies conducted in dimethylformamide (DMF) showed that the metallated polymers exhibited of 412–491 nm. Addition of HCl to the polymer solution caused a bathochromic shift into the range of 515–530 nm. Thermogravimetric analysis (TGA) revealed that the iron moieties were cleaved between 205 and 248 °C while the polyether/thioether backbone degraded between 380 and 613 °C. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (Tg) ranging from 106 to 184°C.This paper is dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contribution to the field of metal-containing polymers.     

Spin Labels as the Instrument for Analysis of Topochemistry of Polymer-Immobilized Ziegler Catalytic Systems

A spin labeling technique was used to investigate the topochemical characteristics of polymer carriers and immobilized metal complexes. Functionalized polyethylenes (PE) such as PE–grafted-polyallylamine (1), PE–grafted-polydiallyl-amine (2), and PE–grafted-poly-4-vinylpyridine (3), obtained by grafting polymerization of the corresponding monomers, were used as polymer carriers. Metal-containing polymers were obtained by immobilization to 2 with either TiCl₄ (2/Ti) or Al(C₂H₅)₂ Cl (2/Al). The stable nitroxyl radical 2,2,6,6-tetramethyl-4-(2-oxy-4,6-dichlorotriazine)piperidine-1-oxyl was used for spin labeling 2 to give , while 2,2,5,5,tetramethyl-3-(N-acetoamidiiodine)-pyrrollidine-1-oxyl was used for spin labeling 3 to give . Radical 2,2,6,6-tetramethyl-4-hydroxy-pyperidine-1-oxyl was bonded to 2/Ti and 2/Al to give and , respectively. The accessibility of the functionalized polymers 1–3 to interact with the spin labels and the immobilized metal complexes was examined. Estimation of the effective distances between the spin labels and the dynamic behavior of nitroxyl radicals in the functionalized polymer matrixes and metal-containing polymers revealed several important features of spin-labeled systems. Metallation of a functional covering makes the polymer more accessible for spin labeling and has a considerable effect on the dynamic characteristics of polymer matrix. A change of the rotational activation energy of the spin labels from 15 kcal/mol in to 44 kcal/mol for in the temperature range 100–150°C was observed.     

Kinetics of the electrochemical deposition of sulfur from sulfide polluted brines

The kinetics of the electrochemical oxidation of sulfide ions in salt water were studied using rotating graphite disc electrodes, polarization techniques, Electrochemical Impedance Spectroscopy (EIS), X-ray Photoelectron Spectroscopy (XPS) and Electron Dispersion Spectroscopy (EDS). Elemental sulfur was shown to be the final product under various temperatures, potentials and times of electrolysis, in amounts that increased with increase in the above variables. The rate of the process is controlled by electron transfer across the interface, while diffusion in the electrolyte has only a modest effect. The apparent reaction orders with respect to the sulfide concentration and pH are 0.60 and 0, respectively. The proposed overall reaction is: while the rate determining step is: The charge transfer coefficient is α_a = 0.23 and the standard rate constant at the equilibrium potential is cm s⁻¹. The degree of coverage of the electrode with sulfur and the polarization resistance of the interface increase, while the current decreases, with the time of electrolysis as more sulfur is deposited on the electrode surface.     

Absolute potential measurements in solid and aqueous electrochemistry using two Kelvin probes and their implications for the electrochemical promotion of catalysis

  The concept of absolute electrode potential in aqueous and solid electrochemistry is discussed in light of the first experimental investigation utilizing a two Kelvin probe system which allows for direct in situ measurement of the work functions of both the, emersed or spillover modified, working and reference electrodes. In both cases, i.e. emersed electrodes in aqueous electrochemistry and spillover-modified electrodes in solid electrochemistry, it is found that the following two equations relate the working–reference electrode potential difference, U _WR, and the work functions, Φ_W and Φ_R of the emersed or spillover-modified working and reference electrodes:

Synthesis and characterization of polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide)

Summary Free radical copolymerization of acrylonitrile (AN, M₁) with poly(2,6-dimethyl-1,4-phenylene oxide)--vinylbenzyl ether (PPO-VBE, M₂, _n + 4200g/mol, _w/ _n + 1.04) was performed at 60°C in either a mixture of N,N-dimethylformamide/toluene or tetrahydrofuran, using 2,2-azoisobutyronitrile (AIBN) as initiator. The characterization of the resulting polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide) (PAN-g-PPO) was performed by 200 MHz ¹H-NMR spectroscopy and solubility.     

[CuL(H2O)2]{[CuL][Fe(CN)6]}2·2H2O (L=3,10-Bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane): A Novel Three-Dimensional Coordination Polymer via H-Bonded Linkages of One-Dimensional Zigzag Chain

A complex with the formula [CuL(H₂O)₂]{[CuL][Fe(CN)₆]}₂·2H₂O, where L=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane, has been synthesized and crystallographically characterized. The structure is composed of a one-dimensional zigzag chain of units, and [CuL(H₂O)₂]²⁺ units. The one-dimensional zigzag chain extents through linkages. The adjacent two polymer chains are linked by the hydrogen bonding between [CuL(H₂O)₂]²⁺ and [Fe(CN)₆]^3–, forming a 3D supramolecular structure with inner hydrophilic channels. Magnetic susceptibility measurements show no exchange interaction between the Cu(II) and Fe(III) ions due to the longer (axial) bond length.     

Effects of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles on the electrodeposition of Zn,Co and ZnCo. I. Electrodeposition in the absence of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electrodeposition of Zn, Co and ZnCo from acid sulfate solutions onto steel was investigated in this first part of a study of the effects of SiC or Al₂O₃ particles on these processes and the formation of ZnCo–SiC and ZnCo–Al₂O₃ electrocomposites. Zn electrodeposition shows a well-defined pre-bulk region, where the hydrogen evolution reaction (HER) and Zn underpotential deposition (upd) compete. Zn bulk electrodeposition begins with primary nucleation and diffusion-controlled growth, strongly dependent on conditions favoring previous Zn upd against HER. It is assumed that this first bulk process takes place over the upd Zn. Zn bulk electrodeposition is followed by secondary nucleation and growth. Co electrodeposition begins with a slow reduction in parallel with HER, followed by a faster reduction. strongly hinders the initial reduction. The ZnCo and Zn electrodeposition curves are initially similar, retaining features of pre-bulk and bulk Zn electrodeposition.     

Fundamental studies on a new concept of flue gas desulphurization

A new process for removal of sulphur dioxide from waste gases is proposed consisting of both electrochemical and catalytic sulphur dioxide oxidation. In the catalytic step a part of the sulphur dioxide is oxidized by oxygen on copper producing sulphuric acid and copper sulphate. The other part is oxidized electrochemically on graphite. The cathodic reaction of this electrolysis is used for recovering the copper dissolved in the catalytic step. The basic reactions of this process have been studied experimentally in detail. It has been shown that sulphur dioxide can be electrochemically oxidized on carbon electrodes to sulphuric acid with high current efficiency. The reaction rate of the electrochemical copper deposition is increased by dissolved sulphur dioxide in the electrolyte. The catalytic oxidation of sulphur dioxide on copper has been investigated for different sulphur dioxide concentrations and temperatures. The ratio of the reaction products, sulphuric acid and copper sulphate, varies over a wide range depending on the experimental conditions.Nomenclature SO₂ concentration (gas phase) (vol % SO₂) - SO₂ concentration (electrolyte) (g l^–1) - E potential vs saturated calomel electrode (V) - E _s specific energy consumption (W g^–1 SO₂) - F Faraday constant (A s^–1 mol^–1) - i current density (mA cm^–2) - molecular weight (g mol^–1) - T temperature (° C) - U _c cell voltage (V) - v _e number of electrons being transferred - space-time yield of SO₂-oxidation (g SO₂ h^–1 dm^–3) - _cu space-time yield of Cu-corrosion (g Cu h^–1 dm^–3) - ratio - fractional conversion of SO₂ - current efficiency for SO₂ oxidation     

Preparation and characterisation of titania-supported vanadium–phosphorus oxide catalysts

A series of vanadium–phosphorus oxides (mainly with V P ) supported on pigmentary anatase (10 m² g^-1) has been prepared using aqueous NH₄VO₃ and (NH₄)H₂PO₄ solutions, with loadings up to 11.3 wt%, equivalent to about 12.7 monolayers. Characterisation by X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction suggests that the main phase present at loadings below about 10 wt% is an amorphous V–P oxide which exists chiefly as blocks of disordered material. The presence of small amounts of crystalline -VOPO₄ and of V₂O₅ is indicated at the highest loadings, especially when and V P ratios are used. The two materials having the lowest loadings are active for methanol oxidation at 473–533 K, and show high selectivity to formaldehyde. This revised version was published online in June 2006 with corrections to the Cover Date.     

Calculation of mean current densities in a two rotating disc electrodes system

A theoretical relationship for mass transfer in the laminar flow region of streaming in a rotating electrolyser was derived by the method of similarity of the diffusion layer for electrodes placed sufficiently far from the rotation axis. The obtained relationship was compared with the known equations valid for systems with axial symmetry. The mean current densities were found from the numerical solution of the convective diffusion equation by the finite-element method and were compared with experimental results.Nomenclature a constant, exponent - c concentration - c ₀ concentration in the bulk phase - C _ij matrix coefficient - D diffusion coefficient - F Faraday constant, 96487 C mol^–1 - h interelectrode distance - j current density - mean current density - J mass flux density - L _j base function - n number of transferred electrons in electrode reaction - n _r outer normal to the boundary - mass flux - N number of nodal points in an element - Q volume rate of flow - mean volume rate of flow - r radial coordinate - r ₀ inner electrode radius - r _l outer electrode radius - r _v radius of inlet orifice - r _d outer disc radius - v _r radial velocity component - v _z normal velocity component - z normal coordinate - thickness of the layer in which the equation of convective diffusion is solved - boundary of the integration domain - thickness of the diffusion layer - _N thickness of the Nernst diffusion layer - v kinematic viscosity - angular velocity - surface Criteria Re _chan channel Reynolds numberQ/hv - Re _loc local Reynolds number,Q/(r + r ₀) - local Reynolds number at mean electrode radius,Q/v(r ₁ +r ₀) - Re _rot rotation Reynolds number, r _d ² /v - modified rotation Reynolds number at mean electrode radius, (r ₁+r ₀)²/4v - Ré _rot modified rotation Reynolds number, (r+r ₀)²/4v - Sc Schmidt number,v/D - Sh _r local Sherwood number,j(r-r ₀)/nFDc _o - mean Sherwood number, - Ta Taylor number,h(/v)^1/2     

Ceramic Precursor Aluminum-Containing Polycarbosilane: Preparation and Structure

The aluminum-containing polycarbosilane (Al-PCS) with various quantities of aluminum was obtained by adding aluminium acetylacetonate (Al(AcAc)₃) as an aluminum source to polysilacarbosilane (PSCS). Subsequently, thermal decomposition and condensation at various conditions were carried out. The molecular weight distribution, yield and softening point of the resulting Al-PCS differ with the Al(AcAc)₃:PSCS weight ratio, the thermolysis temperature and the reaction time. The larger the Al(AcAc)₃:PSCS weight ratio, the higher the thermolysis temperature and the longer the reaction time, the greater the yield and softening point of Al-PCS. In addition, the oxygen and aluminum contents of Al-PCS increase at higher Al(AcAc)₃:PSCS weight ratios. As the mixing weight ratio of Al(AcAc)₃:PSCS increased, additional oxygen was introduced into Al-PCS with the increased Al content. The structure of Al-PCS was characterized by the FT-IR. These results show that Al-PCS is very similar to polycarbosilane in structure.     

The state of Rh during the partial oxidation of methane into synthesis gas

The partial oxidation of methane to synthesis gas over an - and a -supported Rh catalyst has been studied at atmospheric pressure using in situ DRIFTS between 823 and 973 K. A surface intermediate species with IR band at 2000 cm^-1, correlating with the CO formation, was observed during the partial oxidation. DRIFT spectra of adsorbed CO at 323 K were used to study the state of Rh during the partial oxidation. The state of Rh at 973 K is proposed to be a matrix of metallic rhodium with clusters of partially reduced oxide phase with isolated Rh⁺ atoms dispersed on the support. Rh oxide with Rh⁺ cations is the state of Rh during partial oxidation of methane at 823 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrochemical redox reactions of chromium and iron ions in molten NaCl–2CsCl eutectic for pyro-reprocessing of nuclear fuels

Basic electrochemical and spectroscopic properties of Cr³⁺, Cr²⁺, Fe³⁺, and Fe²⁺ were studied to analyze the cyclic redox reactions of Cr and Fe, which may decrease the current efficiency of the electro-winning method using NaCl–2CsCl melts. The formal redox potentials of the and couples, and , in NaCl–2CsCl melts at 923 K were spectroelectrochemically determined to be −0.648 ± 0.005 V and , respectively. These values were determined by measuring electromotive force and UV–VIS absorption spectra at varying concentration ratios of trivalent and divalent ions. Cyclic voltammetry was also carried out to examine the characteristics of the voltammograms for the and couples in NaCl–2CsCl melts. The determined by the spectroelectrochemical method was close to that determined by cyclic voltammetry . The effect of temperature on the in NaCl–2CsCl melts was studied by cyclic voltammetry in the range from 823 to 1,023 K . Diffusion coefficients of Cr³⁺ and Cr²⁺, and , were determined between 823 and 1,023 K to be and , respectively. Molar absorptivities of Cr³⁺ and Cr²⁺ in NaCl–2CsCl melts at 923 K were determined to be 77.8 ± 2.4 M⁻¹ cm⁻¹ at 17,670 cm⁻¹ and 48.0 ± 1.4 M⁻¹ cm⁻¹ at 9,170 cm⁻¹, respectively. In addition, the effects of these ions on the cyclic redox reaction of the pyro-reprocessing process were discussed.     

Controlling Reaction Pathways for Alcohol Dehydration and Dehydrogenation over FeSBA-15 Catalysts

The iron location in FeSBA-15 strongly influences the selectivity to dehydrogenation and dehydration in ethanol conversion. At low iron loading, Fe is present as isolated $\hbox{Fe}^{3+}The iron location in FeSBA-15 strongly influences the selectivity to dehydrogenation and dehydration in ethanol conversion. At low iron loading, Fe is present as isolated species in the amorphous silica phase. At higher loading additional aggregated forms of iron oxide exist. Isolated species in the silica matrix imply Br?nsted acidity resulting in selective formation of ethylene, whereas clusters catalyze formation of ethylene and aldehyde.     

Structure development in polyurethane networks based on star-like precursors

A network formation from an OH-functional star oligomer and two isocyanates (HDI and HDI-trimer) was investigated by changes in the critical molar ratio of OH groups as a function of dilution. The critical ratio is such critical excess of OH groups at which the critical conversion of NCO at the gel point groups reaches 100%. The dilution effect was interpreted by pronounced cyclization, which was higher in the case of the HDI-trimer compared with the HDI.     

Electrodeposited MnO2 as electrocatalyst for carbohydrate oxidation

The electrochemical oxidation of dextrose, fructose and sorbitol under galvanostatic conditions was carried out using both anodically and cathodically deposited MnO₂ layers on platinum and carbon. The coated electrodes showed better electrocatalytic activity for the oxidation of carbohydrates than the bare substrates. Catalytic participation of some higher valent states of manganese in electron transfer relay is speculated, which finds support in the chronopotentiogram and the observed pH-dependence of the electrochemical parameters. The current potential plots showed Tafel behaviour for the MnO₂/Pt electrode. The Tafel slopes were found to be relatively high, indicating kinetic complications. The observed unusual negative values of electrochemical reaction order on MnO₂/Pt electrode were accounted for by considering slow desorption of oxidation products from the electrode surface. The adsorption isotherms of dextrose and fructose on MnO₂ were determined. The current efficiencies of oxidation of carbonyl and hydroxyl groups were found to be and % respectively. SEM pictures showed the cathodically deposited MnO₂ on carbon to be more fine-grained and smoother than the corresponding anodic deposits.     

Molecular weight averages as criteria for quality assessment of heated oils and fats

A simple method for quality assessment of heated oils and fats is described. The proposed method involves precise determination of molecular weight averages (MWA)viz., the weight average molecular weight ( ), the number average molecular weight ( ) and the Z-average molecular weight ( ) by high performance size exclusion chromatography (HPSEC) and their quantitative correlation to percent polar material obtained by column chromatography (CC). Change in MWA on heat treatment of fourteen different edible oils and fats at 180° ± 2°C for eight 8-hr days is studied. Relative standard deviations and regression coefficients of correlation between MWA and their ratios ( , { }, { }, { }, { } and { )vs percent polar material have been reported. Probable discard time was predicted for all the oils based on the above-mentioned correlations and also from the percent of high molecular weight (H. Mwt) species formed. It was observed that the oils which are generally recommended for coronary patients deteriorated faster. A possibility of extending this methodology to the frying oils is suggested. Part of the work was presented at “40th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy” at Georgia World Congress Centre, USA, 1989. IICT Communication No. 2630.     

Nitrogen transformations in a flooded soil in the presence and absence of rice plants: 2. Denitrification

Denitrification rates (d) in a flooded alkaline clay were measured following addition of either to the floodwater, by collecting evolved N₂ + N₂O in an enclosure in the absence or presence of rice plants. Similar estimates of d were obtained in the treatment when the isotopic composition of the enclosed atmosphere was determined using arc redistribution or direct mass spectrometric analysis. Approximately 90% of the gaseous products of denitrification were physically trapped in the soil five days after addition. Mechanical shaking of the soil-water system was an effective method for releasing entrapped gas. Denitrification showed a marked diurnal variation in both and treatments planted to rice, with higher rates during the day than at night. Measured rates of denitrification were higher in planted than in unplanted pots for both and treatments for normal gas sampling. However, evidence was obtained that this was not a real effect, but was due to release of entrapped gas. Denitrification losses corrected for gas entrapment were estimated at <5% of applied . The ¹⁵N mass balance indicated that a much larger amount of applied ammonium (15–25%) was lost by NH₃ volatilisation. The rate of denitrification corrected for gas entrapment was similar to the rate of nitrification estimated by inhibition of ammonium oxidation. Although the inhibitors 2-ethynylpyridine and acetylene prevented denitrification by effectively inhibiting nitrification of , the total recovery of ¹⁵N in the soil-plant system did not increase. The total recovery of was 7–9% higher in the presence than in the absence of rice.     

The IR spectroscopy of methane and hydrogen adsorbed on α-chromia

The vibrational perturbations induced in the IR spectra of methane and of dihydrogen by the non-dissociative adsorption on the (01 2) and (11 0) faces of -chromia are illustrated and compared. It is concluded that both molecules are adsorbed on Cr³⁺ sites and that the involved forces are mainly of the electrostatic type. The resulting situation is compared with that found on the more basic MgO. The problems associated with the C–H and H–H bond activations on transition metal oxides are also discussed.