Molecular-dynamics study of anomalous volumetric behavior of water-benzene mixtures in the vicinity of the critical region

Molecular-dynamics simulations of water-benzene mixtures at 573 K and pressures in the 85-140 bars range have been performed to examine local structure and dynamics of the mixtures, which exhibit anomalously large volume expansion on mixing as recently found by in situ near-infrared measurements. Fractional charges for a simple-point-charge-type potential of water were adjusted so as to reproduce liquid densities and the gas-to-liquid transition pressure of neat water at 573 K. A Lennard-Jones-type potential for benzene was used and the Lorentz-Berthelot combination rule was applied to the water-benzene interaction. Simulations with a N-P-T ensemble of 800-molecule system have been performed and the results reproduce well the anomalous volumetric behavior of the mixtures with the mole fraction of benzene in the 0.3-0.8 range. Pair distribution functions, coordination numbers, and self-diffusion coefficients for the mixtures are calculated, and it is suggested that the local structure around water molecules undergoes drastic change by dissolution of benzene in the vicinity of the critical region, but that around benzene molecules seems to be understood as that of ordinary liquid mixtures.     

Intermolecular Nuclear Relaxations and Molecular Site-Site Pair Correlation Functions in Liquids

Intermolecular nuclear relaxation studies of real liquids and the results of theoretical calculations for model potential functions have provided significant information on the role of molecular interactions in the structure of liquids. The intermolecular proton-proton paircorrelation function (pcf), obtained from the reference interaction site model (RISM) is used as the equilibrium distribution and is used to obtarn an effective force for the calculation of intermolecular proton relaxation rates in liquid benzene, 1,3,5-trideuterobenzene and ethane. For liquid ethane, better agreement with experiment is observed with the pcf obtained from the Monte Carlo simulation than with the RISM result.     

A Monte Carlo study of liquid benzene

A Monte Carlo study for liquid benzene, where the pair potential is described as a sum of Lennard-Jones (12, 6) interactions acting between six equivalent centres of each molecule, has been carried out. The potential parameters have been chosen in such a way that the internal energy and virial pressure were in agreement with the experimental values. The liquid structure has been examined in detail by computing several distribution functions: the radial, the angular correlations and the radial-angular distribution between molecular planes.     

Structure of liquid chlorobenzene in the temperature range 293-363 K

The classical molecular dynamics method is used to simulate the structure of liquid chlorobenzene in the temperature range 293-363 K. Theradial angular distribution functions for the distances between the benzene molecular planes and the angle between them; the radial distribution functions for the distances between chlorine atoms; self-diffusion coefficients, local dipole moments, and permittivities are calculated. In the entire temperature range molecules are joined into agglomerates due to contacts between chlorine atoms (halogen aggregation) and to the specific interactions of benzene rings, which causes mainly parallel and perpendicular orientations of the rings in the first coordination sphere. The molecules in the agglomerates are mostly organized in the 1D motif: chains of chlorine atoms and stacks of benzene rings. With increasing temperature, the agglomerate structure is reorganized, with the most visible changes occurring in temperature ranges 293-298 K, 313-323 K, and 343-353 K.     

Electrosynthesis of Poly(para)phenylene in an Ionic Liquid: Cyclic Voltammetry and in Situ STM/Tunnelling Spectroscopy Studies

The electropolymerization of benzene in the air and water‐stable ionic liquid 1‐hexyl‐3‐methylimidazolium tris(pentafluoroethyl)trifluorophosphate (HMIm)FAP is investigated. The study comprises cyclic voltammetry, IR and in situ STM/tunnelling spectroscopy measurements. The IR results indicate that poly(para)phenylene is the end product of the electropolymerization of benzene in the employed ionic liquid. The resulting conjugation lengths of the product fall between 19 and 21. A polymer reference electrode is used successfully for the electrochemical polymerization of benzene. The first in situ STM results show that the electropolymerization of benzene in the ionic liquid can be probed on the nanoscale and the band gap of the prepared polymer can be determined. The electrodeposited polymer film obtained at a constant potential of 1.0 V vs PPP (polyparaphenylene) exhibits a band gap of 2.9±0.2 eV.     

Vapor-phase chemical equilibrium for the hydrogenation of benzene to cyclohexane from reaction-ensemble molecular simulation

The reaction-ensemble Monte-Carlo (REMC) molecular simulation method was used to study the vapor-phase chemical equilibrium for the reaction of hydrogenation of benzene to cyclohexane. A one-center modified Buckingham exponential-6 (1CMBE6) effective pair potential model (that had already been used to predict thermodynamic properties and liquid–liquid equilibria of helium+hydrogen mixtures) was used for hydrogen. Six-center modified Buckingham exponential-6 (6CMBE6) effective pair potential models (that had already been used to reproduce the saturated liquid and vapor densities, vapor pressures, second virial coefficients, and critical parameters of the six-membered ring molecules), were used for benzene and cyclohexane. No binary adjustable parameters were needed to compute the unlike-pair Buckingham exponential-6 interactions in the ternary system. Simulation results were obtained for the effect of some operating variables such as temperature (from 500 to 650 K), pressure (from 1 to 30 bar), and hydrogen to benzene feed mole ratio (from 1.5:1 to 6:1) on the reaction conversion, molar composition, and mass density of the ternary system at equilibrium. These results were found to be in excellent agreement with calculations using the predictive Soave–Redlich–Kwong (PSRK) group contribution equation of state.     

Molecular dynamics simulation of liquid mixtures of benzene with chlorobenzene

A molecular dynamics method is used to simulate liquid mixtures of benzene and chlorobenzene at different concentrations. Radial angular distribution functions (RADFs) for distances between the benzene ring planes and the angle between them were calculated to analyze the structure of pure components and mixtures. In chlorobenzene, the highest RADF maximum at a distance between the mass centers of the benzene rings of about 4 Å corresponds to the stacked configurations of molecules, and at 5–7 Å the number of stacked contacts are much less than that at 4 Å and is comparable with the orthogonal ones. In liquid benzene, the number of stacked and orthogonal configurations is approximately equal in a range from 4 Å to 7 Å. RADF for benzene reveals extended regions of correlation, which gives evidence of the occurrence of agglomerates bound by specific interactions between the benzene rings. These agglomerates are not characteristic of chlorobenzene, but the presence of maxima on the radial distribution function for the distances between chlorine atoms indicates chlorine aggregation. The effect of halogen aggregation on the structure of benzene-chlorobenzene mixtures is considered. The obtained results are compared with the data on molecular light scattering.     

离子液体催化剂用于煤焦化苯深度脱硫制无硫苯

从扩大有机合成用苯的需求出发,采用研制的离子液体催化剂考察了煤焦化苯深度脱硫制无硫苯的过程。结果表明：N-甲基咪唑硫酸氢盐[Hmim][HSO₄]离子液体催化剂脱噻吩效果与其酸函数值有关。本文采用Hammett指示剂测定离子液体的酸函数H₀,并得出：在-4至-12的范围,离子液体催化剂可以使煤焦化苯噻吩脱至0. 5mg/L以下。与固体酸催化机理相似,酸量和酸强度一定的离子液体催化剂通过Friedel-Crafts反应形成烷基噻吩等,与苯的物性拉开距离,对苯的分离精制是必不可少的,但是过多、过强的[Hmim][HSO₄]酸值也更有利于苯-噻吩-烯烃共聚合等副反应的发生,从而影响离子液体催化剂重复使用的寿命。本研究利用煤焦化苯脱硫反应形成的噻吩衍生物作为提供电荷流通的聚合物,将反复使用后性能不佳的离子液体成分等作为“受电子型”和“给电子型”的掺杂剂,进行导电（抗静电）材料的制备。结果显示：对煤焦化苯脱硫形成的噻吩衍生物等可以用于掺杂导电材料的试制。     

苯在铑电极上吸附的表面增强拉曼散射光谱研究

利用成熟的电极处理方法成功地获得了苯在粗糙铑电极上电化学吸附的拉曼谱图.详细探讨了电极电位、电解质等因素对苯的电化学吸附的影响.结果表明,苯分子吸附到粗糙铑电极上后,表面拉曼谱图与纯苯本体谱图的差别很大,说明吸附后的苯分子在几何及电子结构上发生了巨大变化.苯分子可能以1,3-环己二烯的结构吸附于铑电极表面.     

Structure of ionic liquid-benzene mixtures

Neutron diffraction has been used to investigate the structure of liquid mixtures of 1,3-dimethylimidazolium hexafluorophosphate with benzene. Two concentrations of benzene were investigated, namely, 33 mol % and 67 mol %, and show similar structures in each case. The presence of benzene significantly alters the ionic liquid structure, in particular, in the cation-cation interactions, in agreement with the single-crystal structure described recently (Holbrey, J. D.; Reichert, W. M.; Nieuwenhuyzen, M.; Sheppard, O.; Hardacre, C.; Rogers, R. D. Chem. Commun. 2003, 476). In each case, the data was analyzed using an empirical potential structure refinement process.     

Anisotropic united atom model including the electrostatic interactions of benzene

An optimization including electrostatic interactions has been performed for the parameters of an anisotropic united atoms intermolecular potential for benzene for thermodynamic and transport property prediction using Gibbs ensemble, isothermal-isobaric (NPT) Monte Carlo, and molecular dynamic simulations. The optimization procedure is based on the minimization of a dimensionless error criterion incorporating various thermodynamic data (saturation pressure, vaporization enthalpy, and liquid density) at ambient conditions and at 350 and 450 K. A comprehensive comparison of the new model is given with other intermolecular potentials taken from the literature. Overall thermodynamic, structural, reorientational, and translational dynamic properties of our optimized model are in very good agreement with experimental data. The new model also provides a good representation of the liquid structure, as revealed by three-dimensional spatial density functions and carbon-carbon radial distribution function. Shear viscosity variations with temperature and pressure are very well reproduced, revealing a significant improvement with respect to nonpolar models.     

A note on the elusive 1E2g state in the two-photon spectrum of benzene

An intense, broad feature appears in both two-photon thermal lens and multiphoton ionization spectra of liquid benzene in the 2000–1800 A region. Such bands in liquids of low ionization potential are argued to be direct two-photon excitations into the conduction bands of the liquids, appearing three or more eV below the gas-phase thresholds due to strong solvation of the ionic states. An earlier assignment of the feature in liquid benzene as a transition to the ¹E_2g valence state seems unlikely.     

Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier

Separation of benzene from cyclohexane was performed using two types of liquid membranes, i.e., a supported liquid membrane and a flowing liquid membrane. Silver nitrate was used as the carrier of benzene. The permeation rate of benzene increased with increasing carrier concentration, and the separation factor, which is defined as the ratio of permeability of benzene to that of cyclohexane, was about 630 when the supported liquid membrane prepared by immobilizing 4 mol/L aqueous silver nitrate solution in cellulose filter paper was used. Compared with the supported liquid membrane, the flowing liquid membrane, where a liquid membrane solution was forced to flow in a thin compartment between two microporous membranes, showed one order of magnitude higher permeation rate at high flow rate of the membrane solution. The flowing liquid membrane was very stable and no noticeable decrease in both the flux and the selectivity was observed during 11 days operation. The mechanisms of the facilitated transport of benzene through both types of liquid membrane were proposed. The permeation rate and the selectivity were quantitatively simulated by the proposed model.     

Molecular dynamic simulation of the structure of liquid chlorobenzene, <Emphasis Type="Italic">ortho</Emphasis>-chlorotoluene,and their mixtures

The molecular dynamics method is used to simulate the structure of liquid chlorobenzene, ortho-chlorotoluene, and their mixtures with concentrations of 0.03 ppm, 0.05 ppm, 0.1 ppm, 0.5 ppm, and 0.95 ppm chlorobenzene. Radial angular distribution functions (RADFs) were found for the distances between benzene ring planes and the angle between them in pure components and solutions. The data obtained from RADFs indicate that in the nearest environment of molecules the parallel orientation of benzene rings is the dominant configuration, while the fraction of perpendicular contacts is relatively small. In a concentration range of 0.03 ppm, 0.05 ppm, and 0.95 ppm chlorobenzene, conglomerates form with structural characteristics close to those of the dissolved substance. At a concentration of 0.1 ppm chlorobenzene, solute molecules start to agglomerate. In a concentration range from 0.15 ppm to 0.9 ppm chlorobenzene, both agglomerates and conglomerates of the same size are present in the mixture. The radial distribution functions of chlorine-chlorine distances calculated in pure components and mixtures indicate the presence of chlorine aggregates. The results obtained are compared with molecular light scattering data.     

General algorithm for calculating vibrational–librational states of a rigid molecule in an external potential. Application to benzene–water complexes

A general algorithm of calculating the eigenstates of a rigid molecule trapped in an external potential is reported. The wave function and the potential are expanded about a common reference configuration. The expansion coefficients of the wave function are variationally determined. Contracted basis functions may be used to restrict the number of expansion coefficients. The use of the algorithm is illustrated by calculations of intermolecular eigenstates of benzene–water complexes.     

Correlations between the Rayleigh ratio and the wavelength for toluene and benzene

The values of the Rayleigh ratio of two pure liquid, toluene and benzene, at various wavelengths have been collected from the literature, and a correlation between the Rayleigh ratio and the wavelength in the form of power law has been developed for each liquid and can be used to compute accurately the Rayleigh ratio at any wavelength between 420 and 700 nm. The Rayleigh ratio scales with the wavelength with a power of −4.17 and −4.38, respectively, for toluene and benzene, which deviate significantly from the Rayleigh law (−4.0). However, if the effect of the wavelength on their refractive indexes is accounted for, the power is reduced to −4.0 and −4.2 for toluene and benzene, respectively.     

NMR relaxation of rigid molecules in the nematic phase of a discotic liquid crystal

Frequency and temperature dependent NMR relaxation measurements were performed on deuteriated benzene, pyrene and triphenylene dissolved in the nematic phase of a discotic liquid crystal. The results show a strong frequency dependence of the spectral densities. Based on the symmetries of the system and the usual model for director fluctuations this frequency dependence should be equal for J₁ and J₂. From fitting the commonly used model of rotational diffusion and director fluctuations to the data we see that this is not the case for benzene and triphenylene, even though the fits themselves are satisfactory. Values for the elastic constants, effective viscosity and translational diffusion in similar discotic liquid crystals do not account quantitatively for the frequency dependence of benzene. For both pyrene and triphenylene quantitative comparison was impossible due to lack of translational diffusion data. We also find that the so-called cut-off wave-length is of the order of the dimensions of the liquid crystal molecules, just as in ordinary nematics.