Microwave-assisted synthesis of high-molecular-weight poly(ether imide)s by phase-transfer catalysis

A facile and rapid polycondensation reaction of disodium bisphenol A with bis(chlorophthalimide)s was preformed with a domestic microwave oven in o-dichlorobenzene by phase-transfer catalysis. The polymerization reactions, in comparison with conventional heating polycondensation, proceeded rapidly and were completed within 25 min. The polymerizations gave the corresponding poly(ether imide)s with inherent viscosities of 0.55-0.92 dL g(-1). The effects of various factors on the polymerization, such as the amount of the catalyst, the reaction time, and the microwave power were studied. The properties of the polymers were briefly characterized.

Nickel complexes catalyzed Heck reaction of iodobenzene and methyl acrylate

Nickel appears the most promising for the replacement of palladium among the inexpensive transition metals for that it is active for Heck reaction and about 500 times cheaper than palladium. In this article, we describe our recent results in the area of nickel-catalyzed Heck vinylations. Main focus is on the influence of ligand concentration in different organic solvents and the effects of the addition of water. The conversion is high in NMP and increases with increasing of PPh3/Ni ratio; in ethanol and toluene the conversion presents a maximum value on Ni(PPh3)(2). The effect of the addition of water is sensitive to the concentration of PPh3 and the nature of solvent, it was well explained with the formation and transfer of the active species in the different solvent systems.

Mass transfer kinetics of yttrium(III) using a constant interfacial cell with laminar flow. Part II. Extraction with Cyanex 272

The yttrium(III) extraction kinetics and mechanism with bis-(2,4,4-trimethyl-pentyl) phosphinic acid (Cyanex 272, HA) dissolved in heptane have been investigated by constant interfacial cell with laminar flow. The data has been analyzed in terms of pseudo-first order constants. Studies on the effects of stirring rate, temperature, acidity in aqueous phase, and extractant concentration on the extraction rate show that the extraction regime is dependent on the extraction conditions. The plot of interfacial area on the rate has shown a linear relationship. This fact together with the strong surface activity of Cyanex 272 at heptane-water interfaces has made the interface the most probable location for the chemical reactions. The forward, reverse rate equations and extraction rate constant for the yttrium extraction with Cyanex 272 have been obtained under the experimental conditions. The rate-determining step has been also predicted from interfacial reaction models. The predictions have been found to be in good agreement with the rate equations obtained from experimental data, confirming the basic assumption that the chemical reaction is located at the liquid-liquid interface.

Mass transfer kinetics of yttriium(III) using a constant interfacial cell with laminar flow. Part I. Extraction with Cyanex 302

The interfacial tension is measured for Cyanex 302 in heptane and adsorption parameters are calculated according to Gibbs equation and Szyskowski isotherm. The results indicate that Cyanex 302 has a high interfacial activity, allowing easy extraction reaction to take place at the liquid-liquid interface. The extraction kinetics of yttrium(III) with Cyanex 302 in heptane are investigated by a constant interfacial cell with laminar flow. The effects of stirring rate, temperature and specific interfacial area on the extraction rate are discussed. The results suggest that the extraction kinetics is a mixed regime with film diffusion and an aqueous one-step chemical reaction proposed to be the rate-controlling step. Assuming the mass transfer process can be formally treated as a pseudo-first-order reversible reaction with respect to the metal cation, the rate equation for the extraction reaction of yttrium(III) with Cyanex 302 at pH <5 is obtained as follows:R-f = 10(-7.85)[Y(OH)(2)(+)]((a))[H(2)A(2)]((o))(1.00)[H+]((a))(-1.00)Diffusion parameters and rate constants are calculated through approximate solutions of the flux equation.

Luminescence and energy transfer of organically modified silica xerogels (OMSX) doped and undoped with Eu3+ and Tb3+

Organically modified silica xerogels (OMSX) and Eu3+ (Tb3+)-doped OMSX were prepared by the reaction of (3-aminopropyl) triethoxysilane (APS) with 3-isocyanatepropyltriethoxysilane (ICPTES) followed by the subsequent hydrolysis and condensation in the presence of Eu3+ (Tb3+) via sol-gel method, which were characterized by FT-IR, XRD, fluorescence excitation and emission spectra. The as-formed OMSX shows a strong blue emission with the maximum excitation and emission wavelength at 351 and 420 nm, respectively. Due to the spectral overlap between the emission band of OMSX and f-f absorption lines of Eu3+ and Tb3+ in the UV-blue region, an energy transfer was observed from OMSX host to Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. Excitation at 350-360 nm resulted in a very weak emission around 420 nm from OMSX host and strong emission of Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. The emission spectra of Eu3+ and Tb3+ consist of D-5(0)-F-7(J) (J = 0, 1, 2, 3, 4) and D-5(4)-F-7(J) (J = 6, 5, 4, 3), respectively. Furthermore, the predicted structure of OMSX/Eu3+ and OMSX/Tb3+ is presented.

Studies of electron-transfer and charge-transfer coupling processes at a liquid/liquid interface by double-barrel micropipet technique

Investigation of a heterogeneous electron-transfer (ET) reaction at the water/1,2-dichloroethane interface employing a double-barrel micropipet technique is reported. The chosen system was the reaction between Fe(CN)(6)(3-) in the aqueous phase (W) and ferrocene in 1,2-dichloroethane (DCE). According to the generation and the collection currents as well as collection efficiency, the ET-ion-transfer (IT) coupling process at such an interface and competing reactions with the organic supporting electrolyte in the organic phase can be studied. In addition, this technique has been found to be an efficient method to distinguish and measure the charge-transfer coupling reaction between two ions (IT-IT) processes occurring simultaneously at a liquid/liquid interface. On this basis, the formal Gibbs energies of transfer of some ions across the W/DCE interface, such as NO3-, NO2-, Cl-, COO-, TBA(+), IPAs+, Cs+, Rb+, K+, Na+, and Li+, for which their direct transfers are usually difficult to obtain because of the IT-IT coupling processes, were quantitatively evaluated.

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

Facilitated ion transfer reactions of 20 amino acids with di.benzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, Ile, Phe, Trp, Met, Ala, Gly, Cys, Gln (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (beta(0)), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attributed to the vicinal effect arising from steric hindrance introduced by their side group and the steric bulk effect by lipophilic stabilization.

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA(+)) or ClO4- is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k(12), is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K4Fe(CN)(6) in water when the concentration of TCNQ in the DCE phase is in excess. The k(12) dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ and ferricyanide, k(21), is also obtained by SECM and these results cannot be explained by the same manner.

Mass-transfer kinetics of ytterbium extraction with sec-nonylphenoxy acetic acid

The extraction kinetics of ytterbium with sec-nonylphenoxy acetic acid (CA-100) in heptane have been investigated using a constant interfacial area cell with laminar flow. The influence of stirring speed and temperature on the rate indicated that the extraction rate was controlled by the experiment conditions. The plot of interfacial area on the rate showed a linear relationship. This fact together with the low solubility in water and strong surface activity of CA-100 at heptane-water interfaces made the interface the most probable locale for the chemical reactions. The influences of extractant concentration and hydrogen ion concentration on the extraction rate were investigated, and the forward and reverse rate equations for the ytterbium extraction with CA-100 were also obtained. Based on the experimental data, the apparent forward extraction rate constant was calculated. Interfacial reaction models were proposed that agree well with the rate equations obtained from experimental data.

Promoter effect of La3+ on the electrochemical reaction of microperoxidase-11

The effect of La3+ on the electrochemical behavior and structure of heme undecapeptide-microperoxidase-11 (MP-11)-in the aqueous solution was investigated using cyclic voltammetry, circular dichroism (CD) and UV-vis absorption spectrometry. It was found for the first time that La3+ would promote the electrochemical reaction of MP-11 at the glassy carbon (GC) electrode. This is mainly due to the fact that La3+ would induce more beta-turn and alpha-helical conformations from the random coil conformation of MP-11 and increase the non-planarity of the heme.

Direct electron transfer between hemoglobin and a glassy carbon electrode facilitated by lipid-protected gold nanoparticles

We synthesized a kind of gold nanoparticle protected by a synthetic lipid (didodecyidimethylammonium bromide, DDAB). With the help of these gold nanoparticles, hemoglobin can exhibit a direct electron transfer (DET) reaction. The formal potential locates at -169 mV vs. Ag/AgCl. Spectral data indicated the hemoglobin on the electrode was not denatured. The lipid-protected gold nanoparticles were very stable (for at least 8 months). Their average diameter is 6.42 nm. It is the first time to use monolayer-protected nanoparticles to realize the direct electrochemistry of protein.

Study on transfer and interfacial kinetics of neodymium and samarium in membrane based extraction

Extraction and interfacial kinetics of Nd3+ and Sm3+ with HER/EHP-kerosene in a hollow fiber membrane extractor were studied. The results show that the extraction reactions in the hollow fiber membrane extractor are the same as those in the liquid-liquid extraction, which can be expressed as a quasi-first-order reaction. The effect of acidity in aqueous phase, concentrations of extractant, Nd3+ and Sm3+ on extraction rate were discussed and the corresponding reaction series were obtained. The reaction equations, reaction rate constants and the separation constant were obtained.

Study of electron transfer across the liquid/ice-like matrix interface by scanning electrochemical microscopy

In this work, we report the findings of a study on scanning electrochemical microscopy (SECM) to investigate the interfacial electron-transfer (ET) reaction between the 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ(.-)) in 1,2-dichloroethane and ferricyanide in an ice-like matrix (a mixture of insulting ice and conductive liquid) under low temperatures. Experimental results indicate that the formed liquid/ice-like matrix interface is superficially similar in electrochemical characteristics to a liquid/liquid interface at temperatures above -20 degreesC. Furthermore, imaging data show that the surface of the ice-like matrix is microscopically flat and physically stable and can be applied as either a conductive or an insulting substrate for SECM studies. Perchlorate ion was selected as the common ion in both phases, the concentrations of which controlled the interfacial potential difference. The effect of perchlorate concentration in the DCE phase on interfacial reactions has been studied in detail. The apparent heterogeneous rate constants for TCNQ(.-) oxidation by Fe(CN)(6)(3-) in another phase under different temperatures have been calculated by a best-fit analysis, where the experimental approach curves are compared with the theoretically derived relationships. Reaction rate data obey Butler-Volmer formulation before and after the freezing point, which is similar to most other known cases of ET reactions at liquid/liquid interfaces. However, there is a sharp change observed for heterogeneous rate constants around the freezing point of the aqueous phase, which reflects the phase transition. At temperatures below -20 degreesC, surface-confined voltammograms for the reduction of ferricyanide were obtained, and the ice-like matrix became an insulating one, which indicates that the aqueous phase is really a frozen phase.

Effect of polyvinylidene fluoride hollow fiber membranes on mass transfer of samarium

The influence of swelling and stripping acidity on the mass transfer coefficient based on water phase and the inner diameters of membranes were studied with P507-HCl-Sm as working system in the two different kinds of hollow fiber membranes. Effects of extractant concentration, H+ concentration in aqueous phase and Sm3+ concentration on extraction rate were discussed and the corresponding reaction series were obtained. According to the investigations on the interfacial kinetics, the reaction kinetics equation and reaction rate constant were obtained.

Advances in gas-phase electrophilic aromatic substitution reaction

Recent advances in the gas - phase reaction of aromatics with cationic electrophiles are reviewed. The overall substitution reaction is analyzed in terms of its elementary steps. Mechanistic studies have been focused on the structure and reactivity of covalent and non - covalent ionic intermediates, which display a rich chemistry and provide benchmark reactivity models. Particular attention has been devoted to proton transfer reactions, which may occur intra or intermolecularly in arenium intermediates.