Effect of perchlorate ion within the polypyrrole matrix on the electrooxidation of ethylene glycol in acidic media

The electrooxidation of ethylene glycol was investigated on platinum and perchlorate ions doped polypyroole film electrodes in acidic media. The presence of perchlorate ion was observed by XPS experiments. Optimum experimental conditions were determined. The electrooxidation kinetic of ethylene glycol was studied as a function of ethylene glycol concentration, potential scan limit and scan rate. Results suggest that the doping process has a strong effect on the oxidation reaction.     

PtRu nanoparticles supported on noble carbons for ethanol electrooxidation

In this work, three cytosine derived nitrogen doped carbonaceous materials (noble carbons, NCs) with different atomic C/N ratios and porous networks have been synthesized and used as supports for Pt Ru electrocatalysts in the ethanol oxidation reaction (EOR) for clean hydrogen production. Both, the metal phase and the carbon support play critical roles in the electrocatalysts final performance. Lower NPs size distribution was obtained over supports with low atomic C/N ratios (i.e., 4 and 6) and ...     

Kinetics and mechanism of the formation of glycol esters: Benzoic acid–ethylene glycol system

Esterification-hydrolysis and condensation-glycolysis are the principal equilibria entailed in a system comprised of benzoic acid, ethanediol, ethanediol monobenzoate, ethanediol dibenzoate, and water. These equilibria are characterized by three interrelated equilibrium constants that pertain to the hydrolysis of both ethanediol monobenzoate and ethanediol dibenzoate and to the condensation of ethanediol monobenzoate. The rate constants related to these reactions and to the corresponding reverse reactions were all found to be functions of the concentration of carboxy groups. Antimony triacetate, a well-known transesterification catalyst, catalyzed the condensation reaction strongly but did not affect the esterification reaction. Based on a mechanism that entailed the considered three principal equilibrium reactions, a set of both the kinetic and thermodynamic parameters was obtained by a nonlinear regression procedure. With these parameters the nonlinear rate equations were integrated numerically, using the fourth-order Runge-Kutta method. Excellent agreement between the values thus calculated and the experimental data were obtained in all cases except when considerable concentrations of both benzoic acid and ethanediol dibenzoate were present in the system. It has been concluded that in these instances the formation of the dibenzoate is paralleled by a pyrolysis reaction that is strongly catalyzed by carboxy groups.     

Crystal structures of ethylene glycol and ethylene glycol monohydrate

We have carried out a neutron powder diffraction study of deuterated ethylene glycol (1,2-ethanediol), and deuterated ethylene glycol monohydrate with the D2B high-resolution diffractometer at the Institut Laue-Langevin. Using these data, we have refined the complete structure, including all hydrogen atoms, of the anhydrous phase at 220 K. In addition, we have determined the structure of ethylene glycol monohydrate at 210 K using direct space methods. Anhydrous ethylene glycol crystallizes in space-group P2(1)2(1)2(1) with four formula units in a unit-cell of dimensions a = 5.0553(1) ?, b = 6.9627(1) ?, c = 9.2709(2) ?, and V = 326.319(8) ?(3) [ρ(calc)(deuterated) = 1386.26(3) kg m(-3)] at 220 K. Ethylene glycol monohydrate crystallizes in space-group P2(1)/c with four formula units in a unit-cell of dimensions a = 7.6858(3) ?, b = 7.2201(3) ?, c = 7.7356(4) ?, β = 92.868(3)°, and V = 428.73(2) ?(3) [ρ(calc)(deuterated) = 1365.40(7) kg m(-3)] at 210 K. Both the structures are characterized by the gauche conformation of the ethylene glycol molecule; however, the anhydrous phase contains the tGg' rotamer (or its mirror, g'Gt), whereas the monohydrate contains the gGg' rotamer. In the monohydrate, each water molecule is tetrahedrally coordinated, donating two hydrogen bonds to, and accepting two hydrogen bonds from the hydroxyl groups of neighboring ethylene glycol molecules. There are substantial differences in the degree of weak C-D···O hydrogen bonding between the two crystals, which calls into question the role of these interactions in determining the conformation of the ethylene glycol molecule.     

壳聚糖基大分子引发剂引发寡聚乙二醇甲基丙烯酸酯单电子转移-活性自由基聚合动力学

以O-产溴化壳聚糖（CS—Br）为大分子引发剂,Cu（I）Br为催化剂,通过单电子转移一活性自由基聚合（SET—LRP）,合成了壳聚糖-O-户寡聚乙二醇甲基丙烯酸酯（CS—O-POEGMA）,用原位核磁研究了寡聚乙二醇甲基丙烯酸酯（OEGMA）在不同聚合条件下的聚合反应动力学。结果表明：随着介质pH的降低,配体发生质子化,导致聚合速率下降;在缓冲溶液中,随着CS—Br浓度的升高,反应过程中体系发生凝胶化;pH=5．0的介质中,CS—Br中溴代异丁酸的取代度对反应动力学基本无影响,表明该介质中壳聚糖分子链较舒展,反应可控性最佳．     

Kinetics and Modeling of Vinyl Acetate Graft Polymerization from Poly(ethylene glycol)

A kinetic model for the graft polymerization of VAc from PEG was developed using the method of moments. Experiments were carried out to verify the model. The effect of various parameters, such as initiator concentration, temperature, and PEG molecular weight on the polymerization kinetics was examined. Polymerization rate, grafting efficiency, graft copolymer molecular weight, and PEG grafted ratio were measured. The model was in good agreement with the experimental data. No gel effect was observed at the studied PEG/VAc weight ratio of 1:1. The chain transfer constant to PEG was correlated to be . The model was also applied in a semi‐batch reaction and compared with the experimental results.

     

Recent advances in charge mechanism of noble metal-based cathodes for Li-O2 batteries

Lithium-oxygen(Li-O₂ ) batteries are considered as the next generation for energy storages systems due to the higher theoretical energy density than that of Li-ion batteries. However, the high charge overpotential caused by the insulated Li₂O₂ results in low energy efficiency, side reaction from electrolyte and cathode, and therefore poor battery performance. Designing noble metal-based catalysts can be an effective strategy to develop high-performance Li-O_2...     

Condensed-phase effects on the conformational equilibrium of ethylene glycol

Density functional calculations for ethylene glycol (CH₂OHCH₂OH) in the gas and in a dielectric medium are reported. The condensed-phase calculations are based on the self-consistent reaction field approach and the environment has the dielectric constant of liquid methanol. NPT Monte Carlo simulations of ethylene glycol (ETG) in liquid methanol are also reported. The simulations were carried out for three conformers of ETG (tGg′, gGg′, and tTt). Comparison between SCRF results for the conformational equilibrium in the gas and in the dielectric suggests that the tGg′ conformer is slightly stabilized relative to the gGg′ conformer in the solvent. However, the energy difference between them is less the 1.0 kJ/mol, which indicates that frequent interconversions between the tGg′ and gGg′ conformers are expected in the condensed phase. The all-trans conformer (tTt) is higher than the most stable conformer in the gas by 14 kJ/mol. Monte Carlo simulations predict that the tGg′ and gGg′ conformers have very similar energies in the solvent. However, the simulations also show, in agreement with experimental data, that the tTt conformer is stabilized in liquid methanol, relative to the gas phase. The microscopic mechanism leading to the stabilization of the tTt conformer in the liquid is related to the differential hydrogen-bonding formation between the ETG conformers and the methanol molecules. © 1996 John Wiley & Sons, Inc.     

Theoretical studies on the unimolecular decomposition of ethylene glycol

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T).     

Structure of liquid ethylene glycol

The structure of liquid ethylene glycol (EG) was studied by the vibrational spectroscopy and isothermal compressibility techniques. Raman spectra were recorded at 296 K, IR spectra were measured at 296 and 90 K, and the isothermal compressibility was measured over a pressure range of 0.1–300 MPa. The results obtained were compared with analogous data for water. The structure of liquid EG is discussed using the available literature data on the conformation of its molecule in the gas phase and X-ray diffraction data for crystalline EG. It was concluded that liquid EG has a three-dimensional network of hydrogen bonds, which is more uniform and less mobile compared to water, a feature that explains why the viscosity of EG is high.     

聚乙烯/聚乙二醇共混物中极性组分的表面富集

采用衰减全反射傅立叶变换红外光谱(FTIR-ATR)和扫描电子显微镜研究了极性组分聚乙二醇在聚乙烯／聚乙二醇共混物中的表面富集特性。研究结果认为不同组分表面自由能的差异以及聚乙烯基体的结晶异相排斥作用是导致聚乙二醇组分向共混物表面富集的主要驱动力，而极性组分相区的大小和分布则是影响其选择性迁移过程的重要因素。因此，可以通过添加合适相容剂的办法对聚乙二醇组分的表面富集程度进行有效的调控。     

Preparation of ethylene glycol oligomers

Procedures are described for the preparation of pure nonaethylene glycol and practically pure pentadecaethylene glycol from the monosodium salt and the ditosylate of triethylene glycol, using both toluene and tetrahydrofuran as diluents. The much faster reaction in the latter makes this the preferred reaction medium.     

Kinetics of polyesterification: Adipic acid with ethylene glycol, 1,4-butanediol,and 1,6-hexanediol

Polyesterifications of adipic acid with ethylene glycol, 1,4-butanediol, and 1,6-hexanediol in the absence and presence of the foreign acid (p-toluene sulfonic acid) as catalyst were carried out under constant reaction temperatures of 140–180°C (rather than at constant oil-bath temperatures) and at ratios of diol to diacid of 0.9867–3.5880. The experimental data fit the rate equations proposed by Chen and Wu: d(RCOOR′)/dt = k_ae^αp(RCOOH)²(R′OH) – k_h(H₂O)(RCOOR′) and d(RCOOR′)/dt = k_ac(AH)e^αp(RCOOH)(RO′H) – k_h(H₂O)(RCOOR′) for self-catalyzed and acid-catalyzed reactions, respectively; the data did not fit the other equations appearing in the literature. Here p is the conversion of acid, and α is the constant related to dielectric constants. The reaction rate constants and activation energies for self-catalyzed and acid-catalyzed reactions are calculated. The activation energy is found to decrease with chain length of the alkyl group of the diol. This result is consistent with that observed by Brauman and Blair using ion cyclotron resonance spectroscopy for the variation of acidity of alcohols with chain length of the alkyl group.     

Kinetics of propylene glycol hydrochlorination

The kinetics of hydrochlorination of propylene glycol with hydrogen chloride, both noncatalytic and catalyzed by acetic acid, has been investigated. The type of kinetic equation, pre-exponential factor, activation energy, and empirical coefficients characterizing the chloride ion hydration effect on the rate of propylene glycol hydrochlorination have been determined.     

A conformational study of ethylene glycol

Ab initio calculations were performed for some different conformers of 1,2-ethanediol in order to reveal their relative energies. The equilibrium conformation is of gauche type with a comparatively weak intramolecular hydrogen bond. The energy of the all-trans conformer is 3 kcal/mol above the minimum.     

Kinetics and mechanism of glucose electrooxidation on different electrode-catalysts: Part II. Effect of the nature of the electrode and the electrooxidation mechanism

A comparative study has been made of glucose electrooxidation on electrodes made of metals of group VIII, Ag, Au, Cu and glassy carbon as well as of phthalocyanines and porphyrins of cobalt, manganese and iron. It is found that considerable electrooxidation currents are observed for iridium and rhodium (group VIII), and for gold and copper (the copper subgroup). In neutral and alkaline solutions, glucose electrooxidation rates on gold considerably exceed those on platinum.Investigations have been carried out into the main regularities of glucose electrooxidation on a gold electrode in a wide range of potentials, glucose concentrations and pH values. The effect of chloride ions, gluconic acid and amino acids on glucose electrooxidation on gold have been studied.Proceeding from the direct comparison of adsorption data with polarization data obtained under the same conditions, a mechanism of glucose electrooxidation on platinum has been suggested. It is also shown that the mechanism of glucose electrooxidation on gold is similar, in many respects, to that on platinum.