Supercritical <Emphasis Type="Italic">n</Emphasis>-butane isomerization

Supercritical n-butane isomerization over the solid acid catalysts sulfated zirconia, TiO₂-supported H₄[Si(W₃O₁₀)₄] · xH₂O (Keggin-type heteropoly acid), and H-mordenite is studied in a flow reactor. The critical parameters of n-butane are calculated for a wide range of reaction conditions. Changing from gaseous n-butane to supercritical n-butane markedly extends the lifetime of the catalysts. Under supercritical conditions, the activity and selectivity of the catalysts are invariable, provided that the density of the reaction mixture is in the vicinity of the critical density of n-butane. After the catalysts are deactivated in the gas medium, they can be partially or completely reactivated in the supercritical fluid.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 942–946.Original Russian Text Copyright © 2004 by Bogdan, Klimenko, Kustov, Kazanskii.     

The viscosity of the methanol-<Emphasis Type="Italic">n</Emphasis>-decane system in the region of low <Emphasis Type="Italic">n</Emphasis>-decane concentrations

The kinematic viscosity and density of the methanol-n-decane system were measured at various temperatures at low n-decane concentrations (over the miscibility range). The theory of free volume with taking into account molecular association was used to calculate the dynamic viscosity of this system at 298.15 K. The results substantiated the presence of an anomaly in this system (positive Δlnη values).     

The smallest Hosoya index in (<Emphasis Type="Italic">n</Emphasis>, <Emphasis Type="Italic">n</Emphasis> + 1)-graphs

A (n, n + 1)-graph G is a connected simple graph with n vertices and n + 1 edges. In this paper, we determine the lower bound for the Hosoya index in (n, n + 1)-graphs in terms of the order n, and characterize the (n, n + 1)-graph with the smallest Hosoya index.     

Intramolecular co-operative hydrogen bond in calix[<Emphasis Type="Italic">n</Emphasis>]arenes (<Emphasis Type="Italic">n</Emphasis> = 4, 6, 8) bearing bulky substituents

Based on the Fourier transform IR spectroscopy together with the published NMR and X-ray data, it was shown that cyclic co-operative intramolecular hydrogen bond in calix[n]arene (n = 4, 6, 8) molecules is mainly responsible for their conformational state irrespective of the presence or absence of bulky substituents at the upper rim of the molecules. In accordance with the size of a macrocycle (n = 4, 6, 8), the stable conformation, secured by such a hydrogen bond, constitutes a cone, a pinched cone, and a pleated loop, respectively. The new, potentially competing system of hydrogen bonds in calix[6]arenes with 3-carboxymethyl-1-adamantyl substituents does not affect the conformational state of the macrocycle and its H-bonding. Six carboxy groups at the upper rim form in pairs three cyclic dimers, which does not disturb the hydrogen bonds of the hydroxy groups and the conformation of the macrocycle. In addition, the cavity of the molecule is considerably enlarged. The removal or rearrangement of the guest molecules in the solid calixarene by heating up to 180 °C only slightly affects the conformational state of macrocycles bearing bulky substituents, whereas in calixarenes devoid of such substituents, the similar procedure leads to somewhat of a distortion of the macrocycles (judging from the IR spectral indications of hydrogen bonding). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1062–1068, June, 2007.     

The solubility of C<Subscript>60</Subscript>Br<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 6, 8, 24) in organic solvents

The polythermal (over the temperature range 20–80°C) solubility of fullerene bromo derivatives C₆₀Brn (n = 6, 8, 24) in several solvents (o-xylene, o-dichlorobenzene, n-decanol-1, and enanthic acid) was studied. The corresponding solubility polytherms are given.     

<Emphasis Type="Italic">Ab initio</Emphasis> study of aniline and <Emphasis Type="Italic">n</Emphasis>-propylamine associates with nitrobenzene and <Emphasis Type="Italic">m</Emphasis>-cresol

An ab initio (6-31G**) study of binary associates of aniline and n-propylamine with nitrobenzene and m-cresol has been carried out. The structures corresponding to the total energy minimum of the system have been found for the associates, and their geometrical and energy characteristics have been determined. Basic types of intermolecular interactions have been established, and their effects on the reactivity of the amino group have been investigated.Original Russian Text Copyright © 2004 by I. A. Novakov, V. V. Korolkov, A. I. Pavlyuchko, B. S. Orlinson, and L. A. GribovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 595–601, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Nanosized mixed aggregates of alkylated <Emphasis Type="Italic">p</Emphasis>-sulfonatocalix[<Emphasis Type="Italic">n</Emphasis>]arenes and cetyltrimethylammonium bromide: self-organization and catalytic activity

Self-organization and catalytic activity of supramolecular systems based on a series of O-alkylated p-sulfonatocalix[n]arenes (SCA: n = 4, 6, 8; R = Bu, Oct, Dod (Oct is octyl, Dod is dodecyl)) and cetyltrimethylammonium bromide (CTAB) were studied by dynamic light scattering, tensimetry, and spectrophotometry. In aqueous solutions containing SCA (10^-6-10^-4 mol L^-1) and CTAB (10^-2-10^-12 mol L^-1), mixed associates and SCA—CTAB micelles are formed in a wide concentration range. Their sizes (100–300 nm), properties, and reactivity depend mainly on the structure and concentration of the starting components, as well as on the nature of their associates in solutions. A relationship between the nonlinear concentration dependences of the sizes of SCA—CTAB micelles (SCA: n = 4, 6, 8; R = Dod) and their catalytic activity in the hydrolysis of _O-ethyl _O-(4-nitrophenyl) chloromethylphosphonate was established. The study of the physiological effect on plant cells in solutions of SCA (n = 6; R = Dod), CTAB, and their mixtures showed that SCA and CTAB exerted opposite effects on the energy exchange in the wheat root cells, while a mixed solution of these substances (1: 1) has almost no effect on the physiological state of the roots, which is due to the formation of stable CTAB—SCA aggregates that protect the biosystem from the action of the starting components.     

Host–Guest Complexation of <Emphasis Type="Italic">β</Emphasis>-, <Emphasis Type="Italic">γ</Emphasis>-Cyclodextrin with Alkyl Trimethyl Ammonium Bromides in Aqueous Solution

As a continuation of our previous investigation, interactions between cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and alkyl trimethylammonium bromides in aqueous solutions have been studied with titration calorimetry and ¹H NMR at 298.15 K. The results are discussed in terms of the amphiphilic interaction of CD with surfactants and the iceberg structure formed by water molecules existing around the hydrophobic tail of surfactant molecules. The stoichiometry of the β-CD–surfactant system is 1:1 whereas that of the γ-CD–surfactant system is 1:2. The corresponding formation enthalpy (negative) of the complexes of the two systems decreases with an increase in the number of carbon atoms (n) in hydrophobic chain of surfactant molecule, C _n H_2n+1, whereas the entropy increases with the enlargement of n.     

Mercaptan addition to 1-<Emphasis Type="Italic">O</Emphasis>-allyl-2,3,4,6-tetra-<Emphasis Type="Italic">O</Emphasis>-acetyl-<Emphasis Type="Italic">β</Emphasis>-D-galactopyranose

Addition of ethyl-, propyl-, and n-butylmercaptans to 1-O-allyl-2,3,4,6-tetra-O-acetyl-β-D-galactopyranose in the presence of benzoyl peroxide catalyst was studied for the first time. The products were 1-O-(3-ethylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-galactopyranose, 1-O-(3-propylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-galactopyranose, and 1-O-(3-butylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-galactopyranose. Deacetylation of 1-O-(3-ethylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-galactopyranose produced 1-O-(3-ethylthiopropyl)-β-D-galactopyranose. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 209–211, May–June, 2007.     

Unsteady mass transfer into a sphere under equilibrium condition <Emphasis Type="Italic">y</Emphasis> = <Emphasis Type="Italic">Ax</Emphasis> + <Emphasis Type="Italic">B</Emphasis>

We obtained an analytical solution of a problem of unsteady mass transfer under the equilibrium condition y = Ax + B to compare results with a problem solution in the case of equilibrium condition looking as y = Ax.     

Improvement Method for Synthesis of <Emphasis Type="Italic">p-tert</Emphasis>-butylthiacalix[<Emphasis Type="Italic">n</Emphasis>]arenes; Effect of Using Base Catalyst with Carboxylic Acid

The improved method for synthesis of p-tert-butylthiacalix[n]arenes (TCnAs) by using precursor which is sulfur-bridged oligomer of p-tert-butylphenol with acetic acid and terephthalic acid as a template in a combination with base catalyst such as NaOH and NaH gave much better yields for TC6A (10.6 %) and TC8A (7.8 %), respectively. Such stronger base NaH than NaOH could bring down a reaction temperature for synthesis of TC8A.     

The self-organization properties of <Emphasis Type="Italic">n</Emphasis>-dodecylammonium α-glutamate/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>5</Subscript>H<Subscript>11</Subscript>OH/water system

A biocompatible surfactant-n-dodecylammonium α-glutamate (GDA) with biodegradable and biocompatible properties was synthesized, and the phase behavior and the structural properties of GDA/n-pentanol/water system was studied by small-angle X-ray diffraction, electron spin resonance, and freeze-fracture transmission electron microscopy (FF-TEM). In the ternary phase diagram of GDA/n-pentanol/water system, there exist three isotropic regions—O/W, bicontinuous, and W/O structures, and two anisotropic regions—hexagonal liquid crystal (HEX), and lamellar liquid crystal (LLC) regions. UV irradiation causes the decrease in the interlayer space, d, of lamellar liquid crystal and in the radius, r, of column aggregates of hexagonal liquid crystal, but it has little effect on the structure of O/W and W/O microemulsions.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

Excess molar enthalpy of binary mixtures of hexane+ethyl benzene, <Emphasis Type="Italic">o</Emphasis>-xylene, <Emphasis Type="Italic">m</Emphasis>-xylene and <Emphasis Type="Italic">p</Emphasis>-xylene at 298.15 K

Summary This paper reports excess molar enthalpies of the binary systems hexane+ethyl benzene, hexane+o-xylene, hexane+m-xylene and hexane+p-xylene at 298.15 K and atmospheric pressure, over the whole composition range. The data was measured directly using a Calvet microcalorimeter. The excess magnitude was correlated to a Redlich-Kister type equation for each mixture. Also, we will discuss the results for the four mixtures studied here and by comparison with the same binary systems but containing propyl propanoate as first component. Finally, we will correlate our results with the Nitta-Chao and the three UNIFAC theoretical approximations.     

Solid-liquid equilibria of binary systems containing <Emphasis Type="Italic">n</Emphasis>-tetracosane with naphthalene or dibenzofuran

A differential scanning calorimeter (DSC) was used to determine binary solid-liquid equilibria (SLE) for dibenzofuran+n-C24 and naphthalene+n-C24 mixtures. Results obtained with this technique were compared with those predicted by two modified UNIFAC (Universal Functional group Acitivity Coefficients) versions. This model is employed with the idea to extensively investigate the validity of UNIFAC (Larsen and Gmehling versions). The corresponding activity coefficients were calculated and applied to the prediction of non-electrolyte mixtures real behavior. Reasons of prediction without success in the case of using original interaction parameters, were analysed and discussed. Interesting representation of solubility diagrams was obtained using partly readjusted UNIFAC interaction parameters. The two systems selected can be used for contributing to develop the data base using group contribution methods. For practical purposes, SLE are of interest in chemical process design, especially when process conditions must be specified to prevent precipitation of a solid.     

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C <Subscript>1</Subscript>E<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C <Subscript>1</Subscript> (<Emphasis Type="Italic">n</Emphasis>=1−4)

The hypothesis that the degree of hydration of poly(oxyethylene) (POE) in aqueous solution depends on the mole ratio of water molecules to ether oxygen atoms in the molecule has been verified by studying the isotropic Raman spectra in the O−H stretching region for four short-chain POEs (C ₁E _n C ₁ withn=1−4). Excellent coincidence of the O−H stretching Raman band for all four POEs studied in the range of mole ratio H₂O/O _ether from 25 to 0.6 was observed, thus confirming the assumption stated above. A conclusion that all ether oxygen atoms in the POE molecule participate in hydrogen bonding with water molecules has been made.     

Isothermal catalytic combustion of <Emphasis Type="Italic">n</Emphasis>-pentane/air mixtures on platinum wire

The transient response of the input power necessary to maintain isothermal conditions after a step temperature perturbation applied to a platinum wire immersed in a gaseous fuel/air mixture allows for the measurement of the reaction heat flow rate, directly related to the rate of the catalytic combustion. The S-shaped variation of this rate in time is employed to evaluate the induction period of the catalytic ignition. The effect of mixture composition, total pressure, and catalyst temperature on the induction period for the catalytic ignition of lean to stoichiometric n-pentane/air mixtures on isothermally heated platinum wire is reported and discussed. The mixture composition was varied between 1.40 and 2.56% n-pentane in air, the total pressure between 20 and 101 kPa, and the wire temperature between 470 and 600 K. The reaction rates, turnover frequencies, overall and partial reaction orders, and activation energies were determined from the analysis of the obtained results and compared to other reported data.     

Volumetric properties of 1-iodoperfluorohexane+<Emphasis Type="Italic">n</Emphasis>-octane binary system at several temperatures

New densities are reported over the whole composition range for 1-iodoperfluorohexane+n-octane system at temperatures from 288.15 to 308.15 K at atmospheric pressure. These data have been used to compute the excess molar volumes, V _m ^E. Large positive V _m ^E values have been obtained over the entire range of composition, which increases when the temperature rises. The experimental data were used to calculate the isobaric thermal expansivity, and the quantities (∂V _m ^E/∂T)_p and (∂H _m ^E/∂p)_T. Furthermore, the results have been used to investigate the volumetric prediction ability of the equations of state Soave–Redlich–Kwong, Peng–Robinson, Patel–Teja and Soave–Redlich–Kwong with volume translation.     

Solubility of bromofullerenes C<Subscript>60</Subscript>Br<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 6, 8, 24) in aqueous-ethanolic mixtures at 25°C

Solubility of fullerene bromoderivatives C₆₀Br _n (n = 6, 8, 24) in aqueous-ethanolic mixtures at 25°C were studied. The corresponding solubility isotherms are presented.     

Enthalpies of mixing of <Emphasis Type="Italic">o</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-isomers at 298.15 K

Excess enthalpies (H ^E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H ^E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.