A Numerical Approach for Multicomponent Vapor Solid Equilibrium Calculations in Gas Hydrate Formation

A new numerical approach has been developed for vapor solid equilibrium calculations and for predicting vapor solid equilibrium constant and composition of vapor and solid phases in gas hydrate formation. Equation of state methods generally do a good job of determining vapor phase properties, but for solid phase it is much more difficult and inaccurate. This proposed new model calculates vapor solid equilibrium constant and vapor and solid phase composition as a function of temperature and partial pressure. The results of this proposed numerical approach, for vapor solid equilibrium, have a good agreement with the available reported data. This new numerical model also has an advantage to tune coefficients, to cover different sets of experimental data accurately.     

A Novel Approach to Improve the Detectability of CO2 by GC Analysis

A novel stochastic resonance algorithm was employed to enhance the signal-to-noise ratio (SNR) of signals of analytical chemistry.By using a gas chromatographic data set,it was proven that the SNR was greatly improved and the quantitative relationship between concentrations and chromatographic responses remined simultancously.The linear range was extended beyond the instrumental detection limit.     

L‐Proline–H2O2: A New Chemoselective Approach for Oxidation of Sulfides to Sulfoxides

A facile and selective oxidation of sulfides to sulfoxides using an L‐proline–H₂O₂ system for structurally divergent sulfide substrates with excellent yields at ambient conditions is reported.     

Calculations for the vibration frequencies of the OH⋯O bond in KH2PO4 by a semiempirical method

The frequencies of the stretching vibration and the bending vibration of the OH⋯O bond in potassium dihydrogen phosphate have been calculated by means of two semiempirical formulae with three parameters. The calculated results can give satisfactory explanation for the experimental spectra of the potassium dihydrogen phosphate crystal. The parameters used in the calculations may be related to the chemical bonding and the charge distribution about the two oxygen atoms of the OH⋯O bond system.     

Calculating Equilibrium Constants in the SnCl2–H2O–NaOH System According to Potentiometric Titration Data

Russian Journal of Physical Chemistry A - The potentiometric titration of tin chloride SnCl2 is performed in the concentration range of 0.00009–1.1 mol/L with a solution of sodium hydroxide...     

Solid–Liquid Equilibrium for the Ternary System 2-Methyl-4-Nitroaniline + 2-Methyl-6-Nitroaniline + Ethyl Acetate: Determination and Modelling

The solid–liquid phase equilibria for the ternary system 2-methyl-4-nitroaniline + 2-methyl-6-nitroaniline + ethyl acetate was determined experimentally by the method of isothermal solution saturation at temperatures of (293.15, 303.15 and 313.15) K under the pressure of 101.2 kPa. Based on the obtained solubility data, the isothermal phase diagrams of the system were constructed. At each temperature, there are two pure solid phases formed, which correspond to pure 2-methyl-4-nitroaniline and pure 2-methyl-6-nitroaniline, which was confirmed by Schreinemakers’ wet residue method and X-ray powder diffraction. The crystallization regions of pure 2-methyl-4-nitroaniline and pure 2-methyl-6-nitroaniline increased with decreasing temperature. The crystalline region of 2-methyl-4-nitroaniline was larger than that of 2-methyl-6-nitroaniline at a fixed temperature. The solubility data were correlated with the NRTL and Wilson models. The values of the root-mean-square deviations are 5.01 × 10^?3 for the NRTL model, and 6.43 × 10^?3 for the Wilson model. The solid–liquid equilibria, phase diagrams and the thermodynamic models for the ternary system can provide the foundation for separating 2-methyl-6-nitroaniline or 2-methyl-4-nitroaniline from its mixtures.     

A full-dimensional time-dependent wave packet study of the OH + CO → H + CO<Subscript>2</Subscript> reaction

Full-dimensional time-dependent wave packet calculations were made to study the \(\hbox{OH}+\hbox{CO} \rightarrow \hbox{H}+\hbox{CO}_2\) reaction on the Lakin–Troya–Schatz–Harding potential energy surface. Because of the presence of deep wells supporting long-lived collision complex, one needs to propagate the wave packet up to 450,000 a.u. of time to fully converge the total reaction probabilities. Our calculation revealed that the CO bond was substantially excited vibrationally in the complex wells, making it necessary to include sufficient CO vibration basis functions to yield quantitatively accurate results for the reaction. We calculated the total reaction probabilities from the ground initial state and two vibrationally excited states for the total angular momentum J = 0. The total reaction probability for the ground initial state is quite small in magnitude with many narrow and overlapping resonances due to the small complex-formation reaction probability and small probability for complex decaying into product channel. Initial OH vibrational excitation considerably enhances the reactivity because it enhances the probability for complex decaying into product channel, while initial CO excitation has little effects on the reactivity. We also calculated the reaction probabilities for a number of J > 0 states by using the centrifugal sudden approximation. By doing some calculations with multiple K-blocks included, we found that the centrifugal sudden approximation can be employed to calculate the rate constant for the reaction rather accurately. The calculated rate constants only agree with experimental measurements qualitatively, suggesting more theoretical studies be carried out for this prototypical complex-formation four-atom reaction.     

Phase Behavior and Structural Properties of the Triton X − 100/n − C n H2n + 1OH/H2O System

ABSTRACT

In the Triton X ? 100/n-C_nH_2n + 1OH/H₂O system, the lamellar liquid crystalline region increases and the regions of O/W, W/O and bicontinuous microemulsion domains shrink, simultaneously, with the length of the chain in the unbranched aliphatic alcohol. In the O/W region, the Gibbs free energy for alcohol transfer from the water continuous phase to Triton X ? 100 micellar phase increases linearly with the chain length of alcohol. In the W/O region of the Triton X ? 100/n ? C_nH_2n + 1OH/n ? C₇ H₁₆/H₂O system, as the solubilized water content increases, the effective radius (R _e ), the inner water radius (R _W ), the thickness of the interfacial layer (L) and the average aggregation number ([nbar]) of the reverse micelles increase, whereas the total number (N _d ), the total interfacial area (A _d ) and the change of the standard free energy (Δ _c ? i G ⁰) for alcohol transfer from the oil continuous phase to the interfacial layer of the reverse micelles decrease; and with the longer chain alcohols, the values of R _e , R _W , L, and [nbar] all increase, while the Δ _c-i G⁰ value decreases drastically with increasing chain length. In the lamellar liquid crystalline region, increasing the alcohol chain length can increase the stability of the lamellar liquid crystalline domain. All the results show that the alcohols, n ? C _n H_2n + 1OH, can be used as cosurfactants in the nonionic surfactant system and function similarly as in ionic surfactant systems.     

From strong van der Waals complexes to hydrogen bonding: From CO⋯H2O to CS⋯H2O and SiO⋯H2O complexes

Structures and interaction energies of complexes valence isoelectronic to the important CO?H(2)O complex, namely SiO?H(2)O and CS?H(2)O, have been studied for the first time using high-level ab initio methods. Although CO, SiO, and CS are valence isoelectronic, the structures of their complexes with water differ significantly, owing partially to their widely varied dipole moments. The predicted dissociation energies D(0) are 1.8 (CO?H(2)O), 2.7 (CS?H(2)O), and 4.9 (SiO?H(2)O) kcal∕mol. The implications of these results have been examined in light of the dipole moments of the separate moieties and current concepts of hydrogen bonding. It is hoped that the present results will spark additional interest in these complexes and in the general non-covalent paradigms they represent.     

First-principles Calculations of H2O Adsorption Reaction on the GaN（0001） Surface

The adsorption and decomposition of H2O on GaN（0001） surface have been explored employing density functional theory （DFT）. Two distinct adsorption features of H2O on GaN（0001） corresponding to molecular adsorption and H-OH dissociative adsorption are revealed by our calculations. The activities of the surface reactions of H2O on GaN（0001） surface are investigated. For the stepwise processes of H2O decomposition into H2 in gas phase and adsorbed O atom （H2O（g）→H2O（chem）→OH（chem） ＋ H（chem）→2H（chem） ＋ O（chem）→H2（g） ＋ O（chem））, the first and second steps are facile and can even occur at room temperature; while the last two have high barriers and thus are difficult to proceed, especially the fourth step is endothermic. In short, H2O adsorption and decomposition into H2 in gas phase and adsorbed O atom on GaN（0001） surface are exothermic by -43.98 kcal/mol.     

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal–Organic Framework for Efficient C2H2/CO2 Separation

Rational design of high nuclear copper cluster-based metal–organic frameworks has not been established yet. Herein, we report a novel MOF ( FJU-112 ) with the ten-connected tetranuclear copper cluster [Cu₄(PO₃)₂(μ₂-H₂O)₂(CO₂)₄] as the node which was capped by the deprotonated organic ligand of H₄L (3,5-Dicarboxyphenylphosphonic acid). With BPE (1,2-Bis(4-pyridyl)ethane) as the pore partitioner, the pore spaces in the structure of FJU-112 were divided into several smaller cages and smaller windows for efficient gas adsorption and separation. FJU-112 exhibits a high separation performance for the C₂H₂/CO₂ separation, which were established by the temperature-dependent sorption isotherms and further confirmed by the lab-scale dynamic breakthrough experiments. The grand canonical Monte Carlo simulations (GCMC) studies show that its high C₂H₂/CO₂ separation performance is contributed to the strong π-complexation interactions between the C₂H₂ molecules and framework pore surfaces, leading to its more C₂H₂ uptakes over CO₂ molecules.     

A Mild and Efficient Procedure for the Preparation of Chromone-2-carboxylates

Chromone-2-carboxylates are widely used for the pharmacological activity of several of its derivatives1. The general synthesis of such chromone derivates includes two steps (Scheme 1): a Claison condensation of dialkyl oxalate with 2-hydroxyacetophenones to achieve alkyl 3-(2-hydroxyphenyl)-3-oxopropanoates in the presence of NaH, NaOEt, or NaOMe; cyclodehydration of the alkyl 3-(2-hydroxyaryl)-3-oxopropanoates to obtain chromones under acid condition. The total yield of the two steps is q…     

Direct determination of the rate constant for the reaction CO + N2O → CO2 + N2

The rate constant for the bimolecular reaction CO + N₂O → CO₂ + N₂ was determined by comparison of calculated infrared emission profiles of CO₂ with those observed in shock-tube experiments in the temperature range 1350–2100 K for CO-N₂O-He-Ar mixtures. The rate constant was found to be k₁ = 3.2 × 10¹¹exp(−85 kJ/RT) cm³ mol⁻¹ s⁻¹.     

A priori rate constant for the reaction NH2+NO → N2+H2O

Capture rates for a dipole-dipole+Morse potential, from approximate semiclassical trajectory calculations, have been combined with RRKM rates for passing through entropy bottlenecks on the potential surface for NH₂ + NO → N₂ + H₂O. The resulting overall rate constants are in good agreement with experiment. The effective lifetime of the NH₂NO collision complex is found to be of the order of 10⁻¹¹s at room temperature, which accounts for the observed lack of pressure dependence of the rate constant. Calculated rate constants increase markedly at low temperatures, though not as rapidly as some of the experimental data would indicate.     

Direct ab initio dynamics calculations of thermal rate constants for the CH4 + O2 = CH3 + HO2 reaction

Thermal rate constants of the CH₄ + O₂ = CH₃ + HO₂ reaction were calculated from first principles using both the conventional transition state theory (TST) and canonical variational TST methods with correction from the explicit hindered rotation treatment. The CCSD(T)/aug-cc-pVTZ//BH&HLYP/aug-cc-pVDZ method was used to characterize the necessary potential energy surface along the minimum energy path. We found that the correction for hindered rotation treatment, as well as the re-crossing effects noticeably affect the rate constants of the title process. The calculated rate constants for both forward and reverse directions are expressed in the modified Arrhenius form as \(k_{\text{forward}}^{\text{CVT/HR}} = 2.157 \times 10^{ - 18} \times T^{2.412} \times \,\exp \,( - \frac{25812}{T})\) and \(k_{\text{reverse}}^{\text{CVT/HR}} = 1.375 \times 10^{ - 19} \times T^{2.183} \times \,{\kern 1pt} \exp \,\,(\frac{2032}{T})\) (cm³ molecule^?1 s^?1) for the temperature range of 300–2,500 K. Being in good agreement with literature data, the results provide solid basis information for the investigation of the entire alkane + O₂ = alkyl radical + HO₂ reaction class.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi-M′MOF , pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm⁻³, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂-capture amount of 4.54 mol L⁻¹, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi-M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M′MOF as a promising material for C₂H₂/CO₂ separation.     

Glycerin and CeCl3 · 7H2O: A New and Efficient Recyclable Reaction Medium for the Synthesis of Quinoxalines

An efficient and environmentally benign process for the synthesis of quinoxalines has been developed using glycerine–cerium chloride as a reaction medium. This method is applicable to a variety of diketones and 1,2-phenylenediamines to afford the corresponding quinoxaline derivatives in excellent yields. The reaction medium was recovered and reused for further reactions without any problem.     

Organocatalytic Asymmetric Direct C sp 3H Functionalization of Ethers: A Highly Efficient Approach to Chiral Spiroethers

Spiro compounds: An organocatalytic asymmetric method for the C?sp?3?H functionalization of the α?position of racemic cyclic ethers has been developed. The transformation, mediated by catalytic amounts of an imidazolidinone and strong acid, involves a tandem 1,5-hydride transfer/cyclization and provides access to a structurally diverse series of chiral spiroethers with high levels of enantioselectivity.