Adiabatic compressibility of tetraethylammonium tetrafluoroborate solutions in propylene carbonate

The density and ultrasound propagation velocity for Et₄NBF₄ solutions in propylene carbonate were determined in a concentration range of 0.01–0.8 mol/kg at 283.15, 298.15, and 308.15 K. Apparent molar compressibilities and volumes of the studied electrolyte in solvent were calculated. Solvation numbers and molar adiabatic compressibilities of solvate complexes were determined using the isoentropic compression method. These quantities indicated weak solvation of tetraethylammonium tetrafluoroborate in propylene carbonate in the range of concentrations practically used in ionistors.     

Dielectric properties of propylene carbonate and propylene carbonate solutions

Permittivity data at frequencies from 0.9 to 12 GHz for propylene carbonate and for the solutions of NaI, NaClO₄, Bu₄NI, Bu₄NClO₄, ZnBr₂, and Ca(ClO₄)₂ in propylene carbonate at 25°C are reported and discussed. The contaminating influence of water on the dielectric spectra is shown. Measurements were executed by the method of travelling waves with equipment known to produce data of high precision. Evaluation of the data is performed on the basis of models presupposing one or more relaxation regions. The dielectric spectra of all salts with the exception of ZnBr₂ yield relaxation time distributions with a single critical relaxation time or can be analyzed by assuming two critical relaxation times for the solvent. ZnBr₂ solutions show a supplementary relaxation region at low frequencies which is attributed to the solute. The variation of permittivities at zero frequency with the salt concentration is discussed in the framework of kinetic depolarization. Solvation numbers are estimated.     

Electrochemical properties of a polycrystalline gold electrode in propylene carbonate solutions

The adsorption of 1,6-hexanediol at the Hg—aqueous solution interface was investigated. The differential capacity, interfacial tension and the zero charge potential were measured. Analysis of the results were carried out both at constant charge and at constant potential. Good congruence with respect to the potential and noncongruence with respect to the charge was found. It was shown that the hexanediol molecules orientate flat against the surface and the adsorption could be described equally well by the Frumkin or Flory—Huggins isotherms. Adsorption parameters for the hexanediol were compared with the literature data on adsorption of ethanediol and 1,4-butanediol. It was concluded that adsorption of diols does not affect the thickness of the inner layer. Thus, this adsorption is well described by the model of two parallel capacitors.     

Electrochemical reduction of some graphite fluorides in propylene carbonate

The reduction of graphite fluorides has been carried out in propylene carbonate by the carbon paste electrode technique. Our results confirm the insertion mechanism of Li⁺ ions during the reduction of CF_x in lithium batteries. The shift of the reduction peak towards more negative potentials when LiClO₄ is replaced by nBu₄NClO₄ as the supporting electrolyte is attributed to the difficulty of the bulky cation to intercalate in the host structure. In this paper, the electrochemical behaviour of several CF_x samples is compared, in relation to their crystallinity and composition.     

Electrochemical study of thorium in dimethylsulfoxide and propylene carbonate

Solutions of ThCl₄ in anhydrous dimethylsulfoxide or propylene carbonate have been investigated by dc polarography and controlled potential chronoamperometry on a hanging mercury drop electrode. The results are interpreted by assuming that the cathodic reduction of thorium on mercury proceeds through one step Th(IV)+4 e→Th(0) (E^1/2??1.65V vs. SCE in DMSO); however, the results obtained indicate that the reduction gives rise to the the formation of an autoinhibiting monoatomic layer of thorium; further reduction of thorium on this requires an overpotential (E^1/2??2.15 V vs. SCE in DMSO).The mean value for the maximal superficial concentration of thorium in the film deduced from these experiments equals 1.25×10^?9 mol cm^?2, whereas the value for a hexagonal close-packed layer is 1.5×10^?9 mol cm^?2.     

聚碳酸丙烯酯中碳酸丙烯酯含量的测定

建立了气相色谱分析聚碳酸丙烯酯中碳酸丙烯酯含量的方法,该方法操作简单,准确度高,可满足工业检测需求.     

Polymerization of propylene carbonate

Polymerization of propylene carbonate was carried out at 120–180°C mainly with the use of diethylzinc catalyst. The polymer was a pale-yellow, viscous material of relatively low molecular weight (1000–4000). From the spectroscopic analysis of the polymer and its hydrolyzed product, the polymer was determined to have the structure where x ? 0.50, y ? 0.25, and z ? 0.25. This strongly suggested that the polymerization of propylene carbonate proceeded via 2,7-dimethyl-1,4,6,9-tetraoxaspiro[4,4]nonane (DTN) as an intermediate compound. Hence, DTN was synthesized and polymerized with the use of diethylzinc catalyst. The structure of the polymer thus prepared coincided exactly with that of the polymer from propylene carbonate. From these, a plausible mechanism of the polymerization was developed.     

Structural and electrokinetic characteristics of ultra-and nanoporous glasses in tetraethylammonium chloride solutions

The structural and electrokinetic characteristics of ultra-and nanoporous glasses produced from basic sodium borosilicate glass have been investigated in tetraethylammonium chloride solutions. Colloido-chemical characteristics of the membranes have been compared with those determined in sodium and potassium chloride solutions. It has been found that the regularities of variations in counterion transference numbers and efficiency coefficients are related to a decrease in tetraethylammonium cation mobility in the membranes.     

Raman spectrum of propylene carbonate

The Raman spectrum of propylene carbonate (4-methyl-1,3-dioxolan-2-one) has been recorded and analyzed. Vibrational assignments have been made for many of the observed frequencies on the basis of comparison with accepted assignments for certain vibrational modes in other compounds with close structural similarities.The spectra of propylene carbonate (PC)-water mixtures have been studied over the entire concentration range at 80° and there seems to be little or no interaction except for partial disruption of hydrogen bonding in water by PC. Raman spectra of solutions of LiClO₄ in PC and in PCH₂O mixtures indicate possible salvation of the Li⁺ ion.     

Influence of nanoporous carbon electrode thickness on the electrochemical characteristics of a nanoporous carbon|tetraethylammonium tetrafluoroborate in acetonitrile solution interface

Electrochemical characteristics for the nanoporous carbon|Et₄NBF₄+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et₄NBF₄+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material.     

Cathodic decomposition reactions of propylene carbonate

The cathodic decomposition of propylene carbonate was investigated. Whereas at graphite the reaction occurs with reasonable high current densities predominantly via the formation of alkali metal intercalation compounds (EC mechanism) at active electrode surfaces such as e.g. sintered nickel, copper- or steel-felt, the reaction occurs at rather small current densities by direct electrochemical reduction. In both cases the reaction products are propene and carbonate. An interpretation of the observed effects due to reactions of impurities such as water can be excluded. Solvent decomposition reactions have to be taken into account for the use of solvents as e.g. PC in lithium batteries.     

Calomel reference electrode in propylene carbonate

Measurements of the contact angle of an air bubble against thin films of silver iodide in an electrolyte solution have been made, using the captive bubble technique, as a function of pAg. The receding contact angle reached its maximum value at a pAg=5.4±0.2. This pAg value coincides closely with the isoelectric point of the silver iodide solution interface. A thermodynamic analysis is given which relates the variation of contact angle to the variation of concentration of potential determining ions and surface charge density.     

Ion-molecule interactions in solutions of lithium perchlorate in propylene carbonate + diethyl carbonate mixtures: an IR and molecular orbital study

FTIR spectra have been recorded and analyzed for solutions of lithium perchlorate in propylene carbonate (PC), diethyl carbonate (DEC), and PC + DEC mixtures. It has been shown that the carbonyl stretch bands for PC and DEC are very sensitive to the interaction between Li+ and the solvent molecules. They split with addition of LiClO4, indicating a strong interaction of Li+ with PC and DEC through the oxygen group of PC and both oxygen and ether oxygen atoms of DEC. In conjunction with molecular orbital calculation, the optimized geometries of solvation are given. In addition, solvent separated ion pairs and contact ion pairs were observed in LiClO4/DEC solutions, and no preferential solvation of Li+ in LiClO4/PC + DEC solutions were detected.     

Infrared (attenuated total reflection) study of propylene carbonate solutions containing lithium and sodium perchlorate

Attenuated total reflection infrared spectroscopy was used to examine the concentration dependent solvation of LiClO4 and NaClO4 electrolytes in propylene carbonate (PC). Factor analysis and curve fitting techniques were performed on the measured spectra and the results compared with ab initio computations to provide evidence for ion-solvent solution geometries. Factor analysis of the measured data allowed the identification of the spectrum of ion-associated PC that is uniquely different from the self-associated PC spectrum. The results indicate Li+ and ClO4- ions are contact ion-paired even at relatively low electrolyte concentrations whereas Na+ and ClO4- ions are not, up to approximately 2 mol dm-3.     

Lithium perchlorate (tetrafluoroborate)-diethyl carbonate-propylene carbonate electrolyte systems

The method of sections was used to study the solubility of the components of the LiClO₄ (LiBF₄)-diethyl carbonate (DEC)-propylene carbonate (PC) ternary system at 25°C. The phase diagrams of the systems were plotted and discussed. At this temperature, the solid phase of the LiClO₄-DEC-PC system is pure salt while that of the LiBF₄-DEC-PC system is composed of LiBF₄ and its LiBF₄ · DEC and LiBF₄ · PC crystal solvates. The compositions of the crystallized solid phases obtained graphically by using the method of sections were confirmed by XRD analysis.     

ZnO催化尿素和丙二醇合成碳酸丙烯酯的反应研究

尿素和丙二醇合成碳酸丙烯酯(PC)在热力学上是可进行的。根据ZnO对尿素和丙二醇的催化反应性能,讨论了合成PC的反应历程。结果表明,该反应是分步进行的,首先尿素分解生成氨气和异氰酸,异氰酸与ZnO作用形成异氰酸物种,在丙二醇的作用下生成中间产物羟丙基氨基甲酸酯(HPC),然后由HPC脱氨气生成PC。 ZnO在尿素分解和HPC脱氨气转化为PC的反应过程中起催化作用。     

Synthesis of dimethyl carbonate and propylene glycol from transesterification of propylene carbonate and methanol using quaternary ammonium salt catalysts

Summary The synthesis of dimethyl carbonate (DMC) was investigated through the transesterification of propylene carbonate (PC) with methanol using quaternary ammonium salt catalysts. The reaction was carried out in an autoclave at 120-140 oC under carbon dioxide pressure of 250-400 psig. The main by-product was propylene glycol. The quaternary salts of larger alkyl group and more nucleophilic counter anion exhibited higher catalytic activity. Kinetic studies were also performed to better understand the reaction mechanism. Quaternary ammonium chlorides immobilized on polystyrene supports were also tested for their possible uses as heterogeneous catalysts.