Functionally substituted tetramethylcyclopentadienes: Synthesis of 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene and its use in the synthesis of an organometallic polymer

Reaction of 2,3,4,5-tetramethylcyclopent-2-enone (1) withp-LiC₆H₄OC-Me₂OMe, followed by treatment with aqueous acid afforded 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene (2). This new ligand was then used in the synthesis of the functionally substituted organomolybdenum reagent (η⁵-C₅Me₄-p-C₆H₅OH)Mo(CO)₂(NO) (3). Treatment of a preformed 1/1 styrene/maleic anhydride copolymer ( \(\bar M_n = 1600\) ) with 5 mol% 3 led to chemical incorporation of the organometallic species into the polymer. The final product contained 3 mol% of the organometallic moiety.     

Ferrocenylenesilylene Polymers as Coatings for Tapered Optical-Fiber Gas Sensors

In this paper we report the use of ferrocenylenesilylene polymers as coatings for tapered optical-fiber sensors. The principle of operation of this device is based upon environmentally induced changes in the refractive index of the polymer layer which change the power transmitted through the tapered fiber. The results for two sensor arrays fabricated using the ferrocenylenesilylene polymer [( ⁵-C₅H₄)Fe( ⁵-C₅H₄)MePhSi] _m and copolymer {[( ⁵-C₅H₄)Fe( ⁵-C₅H₄)SiPhMe] _n [( ⁵-C₅H₄)Fe( ⁵-C₅H₄)Me₂Si] _m are presented. We also show that the sensitivity of this device is a function of the taper beat length.     

Hydrogen half-cells in molten salts. A potentiometric investigation of the systems (Pt or Au) H2O/H2, OH− in fused alkali nitrates

The potentiometric behaviour of the hydrogen electrodes (Pt or Au) H₂O-H₂, OH_–has been investigated in molten (Na_0·5, K_0·5)NO₃ at 503 K. In both cases the potential of the indifferent electrode could be expressed by the general equation [H₂O]/[H₂] [OH^–] which is different from the one expected on the basis of a Nernstian behaviour of the theoretical overall system 2H₂O+2e=H₂+2OH^–.The experimental findings are discussed in terms of mechanistic models involving the actual electrode surface and the standard potential for the theoretical (reversible) hydrogen electrode is calculated: =–·0V(versus Ag/Ag⁺ 0·07 M).     

An investigation of catalyst/cocatalyst/support interactions in silica-supported olefin polymerization catalysts based on Cp*TiMe3*

Some of the interactions in an organometallic catalyst/cocatalyst/support material have been studied quantitatively (by analysis of volatiles and surface organometallic fragments) and spectroscopically (by IR, ¹³C and ²⁹Si solid state CP/MAS NMR). The initial product of grafting Cp*TiMe₃ onto an Aerosil silica is the supported organometallic complex SiOTiCp*Me₂, 1, which is thermally unstable. Mild heating generates the supported tetramethylfulvene complex SiOTiFv*(Me), 3, via an intramolecular C–H activation process. Grafting of AlMe₃ onto either 1 or 3 yields a methylene-bridged heterobinuclear complex, (SiO)₂Cp*TiCH₂AlMe₂, 5, and is accompanied by extensive methylation of the silica surface. The direct reaction of AlMe₃ with the unmodified silica leads predominantly to the supported organometallic fragment SiOAl₂(CH₃)₃(CH₂), 6, whose proposed structure includes a bridging methylene and a bridging siloxide ligand. Its reaction with Cp*TiMe₃ generates methane and SiOAl₂(CH₂)₂TiCp*Me₄, 7.Invited contribution to the special volume entitled The Interface between Heterogeneous and Homogeneous Catalysis stemming from the 11th International Symposium on Relations between Heterogeneous and Homogeneous Catalysis.     

Studies on nonisothermal solid state galvanic cells — effect of gradients on EMF

An expression for the EMF of a nonisothermal galvanic cell, with gradients in both temperature and chemical potential across a solid electrolyte, is derived based on the phenomenological equations of irreversible thermodynamics. The EMF of the nonisothermal cell can be written as a sum of the contributions from the chemical potential gradient and the EMF of a thermocell operating in the same temperature gradient but at unit activity of the neutral form of the migrating species. The validity of the derived equation is confirmed experimentally by imposing nonlinear gradients of temperature and chemical potential across galvanic cells constructed using fully stabilized zirconia as the electrolyte. The nature of the gradient has no effect on the EMF.Nomenclature J _i flux of speciesi - X _i generalized forces - L _ij Onsagar coefficient - ₁ electrochemical potential of ions - ₂ electrochemical potential of electrons - T absolute temperature - U ₁ ^* total energy of transfer of the ion - partial molar enthalpy of the ion - Q ₁ ^* heat of transport of the ion - Z ₁ charge on the ion - F Faraday constant - electrostatic potential - ₂ chemical potential of the electron - ₁ chemical potential of the ion - partial entropy of the ion - E _SE EMF developed across the solid electrolyte - E _Pt EMF developed across the platinum lead - ( ₂)_Pt chemical potential of electrons in platinum - partial entropy of electrons in platinum - (Q ₂ ^* )_Pt heat of transport of electrons in platinum - E _cell EMF developed across the whole cell - chemical potential of oxygen - chemical potential of oxygen in its standard state - R universal gas constant - partial pressure of oxygen - relative chemical potential of oxygen - _M relative chemical potential of metal M - a _M activity of metal M     

The performance of porous and gauze electrodes in electrolysis with parabolic velocity distribution

An approximate numerical method for the estimation of the velocity exponent in (small-scale) flow-through porous and gauze electrodes is presented. The method can also be employed to determine if a plug-flow or a parabolic-flow model offers a more reliable representation of the experimental behaviour of the electrode.Nomenclature a cross sectional area of the electrode - B integration parameter (Equations 7 and 8) - c exit active ion concentration, its mean measured value in the case of parabolic flow,c _o its inlet value;c _m its mean value; its mean calculated value in the case of parabolic flow;c ^* dimensionless concentration, equal toc/c _o; mean dimensionless concentration, equal to /c _o - F Faraday's constant - i _L mean limiting current density (geometric-area base) - j proportionality factor (Equation 1) - k _m mass transport coefficient, its mean value - L length of the electrode - n number of electrons involved in the electrode reaction - N ionic flux - r radial coordinate - R _E geometric radius - R limiting degree of conversion - s specific surface area of the electrode (surface per volume) - u linear solution velocity; u_o its maximum (centreline) value; its mean value (=u_o/2) - v volumetric flow rate; its mean value - x transform variable forz - z dimensionless radial distance - velocity exponent for mass transport (Equation 1)     

Influence of Rare Earth (Ce, Sm, Nd, La, and Pr) on the Hydrogenation Properties of Chloronitrobenzene Over Pt/ZrO2 Catalyst

The effect of rare earths (Sm, Pr, Ce, Nd, and La) on the hydrogenation properties of chloronitrobenzene (CNB) over Pt/ZrO₂ catalyst was studied in ethanol at 303K and normal pressure. The results show that the hydrogenation of CNB can be carried out over Pt/ZrO₂ catalyst. The order of the hydrogenation rates of CNB is p>m>o, and the yield of chloroaniline (CAN) is p>o>m. The specific rate constant turnover frequency (TOF) expressed per surface Pt atom increases when the platinum catalyst is modified by rare earth. The conversion of CNB is >99% and CAN is the main product in the hydrogenation of CNB over PtM/ZrO₂ catalysts. The PtPr/ZrO₂ catalyst shows the best selectivity of CNB to CAN: 89.4mol% for o-CAN, 94.6mol% for m-CAN and 95.1mol% for p-CAN.     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Flow-through and flow-by porous electrodes of nickel foam. I. Material characterization

This paper deals with the characterization of three nickel foams for use as materials for flow-through or flow-by porous electrodes. Optical and scanning electron microscope observations were used to examine the pore size distribution. The overall, apparent electrical resistivity of the reticulated skeleton was measured. The BET method and the liquid permeametry method were used to determine the specific surface area, the values of which are compared with those known for other materials.Nomenclature a _e specific surface area (per unit of total volume) (m^–1) - a _s specific surface area (per unit of solid volume) (m^–1) - (a _e)_BET specific surface area determined by the BET method (m^–1) - (a _e)_Ergun specific surface area determined by pressure drop measurements (m^–1) - mean pore diameter (m) - mean pore diameter determined by optical microscopy (m) - mean pore diameter using Ergun equation (m) - e thickness of the skeleton element of the foam (m) - G grade of the foam (number of pores per inch) - P/H pressure drop per unit height of the foam (Pa m^–1) - r electrical resistivity ( m) - R _h hydraulic pore radius (m) - T tortuosity - mean liquid velocity (m s^–1) Greek symbols mean porosity - circularity factor - dynamic viscosity (kg m^–1 s^–1) - liquid density (kg m^–3) - pore diameter size dispersion     

Synthesis gas formation by direct oxidation of methane over Rh monoliths

The production of H₂ and CO by catalytic partial oxidation of CH₄ in air or O₂ at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10^–4 and 10^–2 s and compared to previously reported results for Pt-coated monoliths. Using O₂, selectivities for H₂ ( ) as high as 90% and CO selectivities (S _CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O₂ instead of air. The superiority of Rh over Pt for H₂ generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H₂ than on Pt, on which the O+ H OH reaction is much faster.This research was partially supported by DOE under Grant No. DE-FG02-88ER13878-AO2.     

Some Factors Influencing the Morphology of α-Zirconium Phosphate and its Intercalation Reactions with a Bifunctional Thioether Amine

Crystalline samples of -zirconium phosphate, (-ZrP, -Zr(HPO₄)₂·H₂O) have been prepared by decomposition of zirconium fluoride complexes in the presence of phosphoric acid under a variety of conditions. The crystallinity and morphology have been shown to depend on a number of factors including the F^–/Zr⁴⁺ ratio, the concentration of Zr⁴⁺ ions, the material of the reaction vessel and the reaction temperature. Under conditions of rapid precipitation small plate-like crystals of -ZrP are produced whereas under conditions of slow crystallisation larger crystals with a lower aspect ratio are formed. The relative intensities of the d ₀₀₂, d ₁₁₀ and d ₁₁₂ reflections observed by X-ray powder diffraction show a correlation with the crystal morphology as determined by SEM.The intercalation reaction of 4-(methylmercapto)aniline with different samples of -ZrP under a variety of conditions has been studied. Incomplete intercalation is observed in each case, with the extent of intercalation depending on both the morphology of the -ZrP and the reaction conditions. The intercalated amine has been shown to exist as a mixture of protonated cations and neutral molecules.     

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     

Characterization of metal-ion containing polyesters

Summary The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ( ) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (c_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in c_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,, which is the corresponding T_g of a polymer of infinite molar mass.     

Synthesis and Redox Properties of a π-Conjugated Cyclobutadienecobalt Polymer Containing Ferrocenyl Groups

The reaction of CpCo(PPh₃)₂, in which Cp= ⁵-cyclopentadienyl, with a -conjugated diacetylene, FcCC–o-C₆H₄–CCFc, in which Fc=ferrocenyl, was found to give a cyclobutadienecobalt mononuclear complex, { ⁴-C₄Fc₂(o-FcC₆H₄)₂}CoCp (1), the crystal structure of which was determined by X-ray crystallography. In contrast, the reaction of CpCo(PPh₃)₂ with FcCC–p-C₆H₄–CCFc affords a cyclobutadienecobalt polymer, [p-C₆H₄( ⁴-C₄Fc₂)CoCp] _n (2). The monocobalt complex 1 shows reversible 1e^– and 3e^– redox waves at E ⁰=0.116 and 0.350 V vs Ag/Ag⁺, and the polymer complex 2 shows two chemically reversible redox waves at E ⁰=0.143 and 0.219 V for the oxidation of the ferrocenyl moieties in the cyclic voltammogram. Crystal data are as follows: (1, C₆₅H₄₉CoFe₄), triclinic, space group P\={1} (No. 2), a=13.547(4), b=16.197(4), c=11.763(4) Å, =106.79(2), =97.93(3), =97.12(3), V=2410(1) ų, Z=2.     

Adsorbed Atoms and Molecules Destined for a Reaction

The idea of an activation complex is popular for explaining reaction rates, but the characteristics of reactions and catalysis may not be explained in this way. A predestined state for each reaction composed of surface atoms and adsorbed species is responsible for these features. Two single Sn atoms trapped in adjacent half-unit cells of an Si(111) 7 × 7 surface is an example of a predestined state. An isolated Sn atom in a half-unit cell does not migrate to other half-unit cells at room temperature, but when two single Sn atoms are in adjacent half-unit cells they undergo rapid combination to form an Sn₂ dimer. In addition, these two single Sn atoms replace the center Si adatoms and an Si₄ cluster is formed. The spatial distribution of molecules desorbing from surfaces may reflect the predestined states for the desorption processes. The spatial distribution in the temperature-programmed desorption (TPD) of NO on Pd(110) and Pd(211) surfaces and that in the temperature-programmed reaction (TPR) of NO + H₂ were studied. N₂ desorbing from Pd(110) by the recombination of N atoms obeys cos⁶ – cos⁷ but the N₂ produced by a catalytic reaction of NO with H₂ obeys cos. In contrast, the N₂ desorbing with NO at 490 K in the TPD of Pd(110) shows a sharp off-normal distribution expressed by cos⁴⁶( – 38). The adsorption of NO on Pd(211) predominantly occurs on the (111) terrace but the spatial distribution suggests that the predestined states for the reaction and desorption are formed on both the (111) terrace and (100) step surfaces.     

Axial dispersion in electrolyte flow through anisotropic packed beds

The axial dispersion of an electrolyte flowing through fixed beds was determined using a polarographic method with two-point measurement. Axial dispersion coefficients at various flow rates were obtained in fixed beds composed of glass beads in order to test the experimental method. Further experiments were performed using square-based parallelipipedic particles (so-called flat plates) defined by the ratioe/a of the thickness,e, over the side,a of the plate. The influence of the ratioe/a on the axial mixing was studied. The experimental data were expressed in the form of empirical correlations giving the Peclet number as a function of the Reynolds number: these two adimensional numbers were based on the interstitial velocity and the equivalent particle diameter. For the flat plate fixed beds, which form very anisotropic porous media, the axial dispersion was greater (up to a factor of 10) than that obtained in the isotropic porous media of spherical particles. The results were explained by the velocity fluctuations within a cross section.Nomenclature a side of the flat plates - a _vs specific surface area - C tracer concentration - C ,C _exp ^" ,C _cale ^" adimensional tracer concentrations - D diffusion coefficient - D _ax axial dispersion coefficient in fixed beds - D _sx axial dispersion coefficient in the pore i - d _p=6/a _vs equivalent particle diameter - e thickness of the flat plates - f friction factor - F _r transfer function - J _L limiting diffusional current - k mass transfer coefficient - L distance between the two sensors - p probability of axial displacement - Pe=uL/D _ax Peclet number - Pe _i=ud _v /D _ax interstitial Peclet number - Pe=2ru ₁/D _ax pore Peclet number - r ₁ radius of the pore i - average pore radius - Re=u ₀ d _p/v superficial Reynolds number - Re _i=ud _p /v interstitial Reynolds number - Re _t=2ru _t/v pore Reynolds number - S surface area of the sensors - Se=v/D Schmidt number - mean residence time - u interstitial velocity - u ₀ superficial velocity - area-averaged fluid velocity in the pores - area-averaged fluid velocity in the pore i Greek letters variation coefficient - P/L pressure drop per length unit - bed porosity - kinematic viscosity - electrolyte density - standard deviation - bed tortuosity     

[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.     

Flow-through and flow-by porous electrodes of nickel foam Part III: theoretical electrode potential distribution in the flow-by configuration

This paper deals with the theoretical potential distribution within a flow-by parallelepipedic porous electrode operating in limiting current conditions in a two-compartment electrolytic cell. The model takes into account the influence of the counter-electrode polarization and of the separator ohmic resistance. The results show that the design of the porous electrode requires the knowledge of the solution potential distribution within the whole cell volume.Nomenclature a _c specific surface area per unit volume of electrode - C ₀ entrance concentration (y=0) - C _s exit concentration (y=y ₀) - E electrode potential (= _M – _S ) - E _o equilibrium electrode potential - F Faraday number - i current density - mean mass transfer coefficient - K parameter [a _ea zFi _oa/(_a RT)]^1/2 - L porous electrode thickness - n number of terms in Fourier serials - P specific productivity - Q volumetric flow-rate - mean flow velocity based on empty channel - V constant potential - V _R electrode volume - x thickness variable - X conversion - y length variable - y ₀ porous electrode length - z number of electrons in the electrochemical reaction Greek symbols parameter - parameter - ionic electrolyte conductivity in pores - _S solution potential - _M matrix potential ( _M = constant) - parameter [=n/y ₀ - parameter [=+K] - overpotential Suffices a anodic - c cathodic - eq equilibrium - s separator - S solution     

Long service life IrO2/Ta2O5 electrodes for electroflotation

Ti/IrO₂-Ta₂O₅ electrodes prepared by thermal decomposition of the respective chlorides were successfully employed as oxygen evolving electrodes for electroflotation of waste water contaminated with dispersed peptides and oils. Service lives and rates of dissolution of the Ti/IrO₂-Ta₂O₅ electrodes were measured by means of accelerated life tests, e.g. electrolysis in 0.5M H₂SO₄ at 25°C and j = 2 A cm^–2. The steady-state rate of dissolution of the IrO₂ active layer was reached after 600–700 h (0.095 g Ir h^–1 cm^–2) which is 200–300 times lower than the initial dissolution rate. The steady-state rate of dissolution of iridium was found to be proportional to the applied current density (in the range 0.5–3 A cm^–2 ). The oxygen overpotential increased slightly during electrolysis (59–82 mV for j = 0.1 A cm^–2 ) and the increase was higher for the lower content of iridium in an active surface layer. The service life of Ti/IrO₂ (65 mol%)-Ta₂O₅ (35 mol%) in industrial conditions of electrochemical devices was estimated to be greater than five years.List of symbols a constant in Tafel equation (mV) - b slope in Tafel equation (mV dec^–1) - E potential (V) - f mole fraction of iridium in the active layer - j current density (A cm^–2) - l number of layers - m _Ir content of iridium in the active layer (mg cm^–2) - r dissolution rate of the IrO₂ active layer (g Ir h^–1 cm^–2) - T _c calcination temperature (°C) - _{O 2} oxygen overpotential (mV) - _{O 2} difference in oxygen overpotential (mV) - _A service life in accelerated service life tests (h) - _S service life in accelerated service life tests related to 0.1 mg Ir cm^–2 (h) - _p polarization time in accelerated service life tests (h)