ZnZSM-5沸石上某些环烷烃芳构化性能的研究

用脉冲微反技术研究了环己烷、甲基环己烷和甲基环戊烷在ZnZSM-5和HZSM-5上反应的产物分布和动力学、发现在ZnZSM-5上, 环己烷和甲基环戊烷以高选择性转化成苯, 甲基环己烷以高选择性转变为甲苯; 在HZSM-5上它们反应的芳烃选择性均很低且都得到以甲苯为主的BTX混合物。证明了这些反应都为动力学一级反应,求出了370 ℃—450 ℃间反应的速度常数和活化能。还发现环己烷反应的苯选择性与催化剂中的Zn含量有一致的对应关系。提出了ZnZSM-5上环烷烃反应的过程图式, 认为芳构化过程的控制步骤是环状碳离子的形成, 反应中非预计芳烃组分的产生与中间体环状碳离子的低温烷基化和高温脱烷基以及裂解所产生的小分子的再芳构化有关。     

Effects of the Presence of Cyclohexane or Methylcyclohexane on the Densities and Volumetric Properties of the Mixture (Benzene + Propionitrile)

Excess molar volumes, V_m^E, have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + cyclohexane or methylcyclohexane) + (propionitrile + cyclohexane or methylcyclohexane)] from the densities measured by means of a vibrating-tube densimeter at atmospheric pressure and a temperature of 298.15 K. The values of V_m^E have been correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, cyclohexane or methylcyclohexane, has a significant effect on the interaction between benzene and propionitrile.     

Volumetric Properties of Ternary-Pseudobinary Mixtures Containing Benzene and Cyclohexane

Densities have been measured as a function of composition for ternary-pseudobinary mixtures of [(benzene + toluene or methylcyclohexane) + (cyclohexane + toluene or methylcyclohexane)] by means of a vibrating-tube densimeter at atmospheric pressure and the temperature 298.15 K. The excess molar volumes, V_m^E, were calculated from the densities and correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show the third component, toluene and methylcyclohexane, influences the interaction between benzene and cyclohexane.     

Excess Molar Enthalpies of Cyclic Ethers with Cyclohexane, Methylcyclohexane, or Chlorocyclohexane

Excess molar enthalpies for mixtures of tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran or 2,5-dimethyltetrahydrofuran with cyclohexane, methylcyclohexane, or chlorocyclohexane were determined at 25°C. The excess enthalpies are positive for the mixtures containing cyclohexane or methylcyclohexane, but negative for the mixtures containing chlorocyclohexane. The results were used with the Prigogine–Flory–Patterson theory to predict the corresponding excess molar volumes.     

OCTA-ALKYL ZINC PHTHALOCYANINES: POTENTIAL PHOTOSENSITIZERS FOR USE IN THE PHOTODYNAMIC THERAPY OF CANCER

The synthesis, characterization and electronic spectra of a series of nine 1,4,8,11,15,18,22,25-octa-alkyl zinc phthalocyanines (ZnPc), potential photosensitizers for the photodynamic therapy of cancer, are described. The substituents on the phthalocyanine (Pc) macrocycle “red-shift” the absorbance maximum, in cyclohexane, of all nine members of this series to a value of 703 ± 2 nm, with a corrected fluorescence emission maximum for the octadecyl derivative of 715 nm. The solubilities and degree of aggregation of six examples in cyclohexane have been measured. The highest homologue, the octadecyl derivative, remains essentially unaggregated to a concentration of 1.5 ± 10^?4 mol dm^?3. The photostability of this Pc has been examined and the compound shown to be sensitive to photooxidation processes, which lead to its decomposition to 3,6-fcw-decylphthalimide. Known singlet oxygen quenchers inhibit the photodecomposition. In a comparative study, the octadecyl ZnPc underwent a more rapid photodecomposition than the corresponding metal-free derivative.     

An NMR study of phenol self-association

This paper presents a study of the chemical shift of the phenol hydroxyl group as a function of concentration and temperature in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. The chemical shift of monomeric phenol has been found. For these solutions monomertrimer equilibrium is observed within the entire temperature range and within a wide concentration range. At low phenol concentrations, from 1 to 3 mole-%, the monomer-dimer equilibrium is observed in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. Chemical shift of the hydroxyl group of trimeric phenol is temperature-dependent. From the experimental data the association constants and thermodynamic functions of the systems under study have been determined. The association constants differ for the above systems at the same temperatures. Association entropy ΔS changes from one system to another, while ΔH is the same for all systems.     

Liquid-liquid equilibria of (cyclohexane + acetonitrile + methylcyclohexane + toluene) and of {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene} at 298.15 K

Tie-line results at 298.15 K and atmospheric pressure are reported for (cyclohexane + acetonitrile + methylcyclohexane + toluene) and for {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene). The extended UNIQUAC and UNIQUAC equations are used to correlate binary vapour-liquid equilibria and mutual solubilities for 10 mixtures constituting the ternary mixtures and to predict the ternary and quaternary liquid-liquid equilibria by use of only binary parameters.     

The yield of solvent excited states in the radiolysis of cyclohexane solutions

It is confirmed by pulse radiolysis that emitting solvent excited states are produced in the radiolysis of n-hexane, methylcyclohexane and cyclohexane. The emission is quenched by benzene and benzene emission appears. Applying stern - volmer kinetics to emissions from solvent, benzene and toluene in cyclohexane a very high energy transfer rate constant, viz., k = 2.8 × 10¹¹M⁻¹ sec⁻¹ is obtained. The yield of the excited state of cyclohexane is not greater than 0.3, and it is concluded that the major part of the excited states of other aromatics produced in cyclohexane solutions comes from ion neutralisation.     

Proprietes physico-chimiques de reseaux polymeriques modeles—II. Influence de la temperature

Polystyrene gels were prepared by anionic copolymerization of styrene and divinylbenzene in dilute solution. There has been a study of the stress-birefringence, as a function of temperature, of these networks swollen to equilibrium in cyclohexane and methylcyclohexane.     

Probing the interaction of solvents with the stationary phase of C18 high-performance liquid chromatographic column material by variable-temperature dependent 129Xe nuclear magnetic resonance spectroscopy

VT (129)Xe NMR was applied to probe the interactions of solvents having different polarity indices with the stationary phase of a RP-C18 HPLC column material. It was observed that the highly polar ethylene glycol molecules do not mix with the alkyl chains of the RP-C18 stationary phase and the solvent is unable to enter the pores and the spaces between the particles. Three phases in this sample are defined as stationary/xenon phase, xenon gas phase (in the pores and the spaces between the particles) and ethylene glycol/xenon phase. In contrast to ethylene glycol, the nonpolar solvent cyclohexane was observed to be well mixed with the RP-C18 stationary phase. The capillary rise effect allows the solvent to enter the pores and the spaces between the particles. Two phases in this sample are defined as stationary/cyclohexane/xenon phase and cyclohexane/xenon phases. The properties of ethyl acetate are between those of ethylene glycol and cyclohexane. The (129)Xe NMR results show that the rational reversed phases should be conditioned from highly solvating to more polar solvents to remove the trapped air. The (129)Xe NMR results also show that pure stationary phase exists only when a highly polar solvent is used in reversed-phase chromatography. For a solvent with lower polarity, a stationary/solvent phase actually forms. This, together with the mobile phase, determines the selective factor for separating mixtures.     

The photoprotector mechanism of mycosporine-like amino acids. Excited-state properties and photostability of porphyra-334 in aqueous solution

The photostability and photophysical parameters of an aqueous solution of the mycosporine-like amino acid (MAA) porphyra-334 have been determined. The excited-singlet state lifetime, measured by time-correlated single photon counting, was 0.4 ns. Laser flash photolysis experiments at 355 nm did not show any transient species. The triplet state of porphyra-334 was sensitized by triplet-triplet energy transfer. The T-T absorption spectrum was determined and the maximal absorption coefficient at 440 nm was estimated to be 1 x 10(4) M(-1) cm(-1). In this way an upper limit for the intersystem crossing quantum yield was determined. The very low quantum yield of fluorescence (phiF = 0.0016) and triplet formation (phiT < 0.05) together with a photodecomposition quantum yield of 2-4 x 10(-4), in the absence and the presence of oxygen respectively, can be explained by a very fast internal conversion process. These results support the photoprotective role assigned to this MAA in living systems.     

Copolymerization of vinyl cyclohexane and α-methyl vinyl cyclohexane with acrylonitrile

Copolymerization of vinyl cyclohexane and α-methyl vinyl cyclohexane with acrylonitrile in the presence of a complexing agent AlEtCl₂ results in the formation of alternate copolymers. In the copolymerization of vinyl cyclohexane with acrylonitrile the copolymer composition depends on the ratio of acrylonitrile to AlEtCl₂. If this ratio is unity, alternating copolymers of the composition 1:1 are formed; with a ratio greater than unity statistical copolymers that contain more than 50% acrylonitrile units are produced. The ¹H-NMR spectroscopy measurements indicate that the interaction between the comonomers and the complexing agent leads to the formation of ternary donor–acceptor complexes of equimolar composition. The equilibrium constants of these complexes at ?60°C have been determined. The effects of temperature, nature of solvent and dilution on the yield, and composition of the copolymers of vinyl cyclohexane with acrylonitrile formed have been studied. By lowering the temperature the yield of copolymers increases but their composition remains equimolar. An increase in the polarity of the medium results in an increase in copolymer yield, whereas the yield decreases if the reaction is conducted in a donor-solvent medium. Dilution of the reaction mixture disrupts the alternation of units in the macrochain of copolymers. The kinetic pecularities of copolymerization have been investigated. The linear dependence of the copolymerization rate on the product of comonomer concentration is observed. The rate of copolymerization is proportional to the square root of the incident light intensity. Various additions of radical type and irradiation accelerate the process of copolymerization. The mechanism of alternating copolymerization of vinyl cyclohexane monomers with acrylonitrile in the presence of AlEtCl₂ is discussed in terms of homopolymerization of the comonomer complex.     

Gas sorption environments in poly(2,6‐dimethyl‐1,4‐phenylene oxide) by xenon‐129 nuclear magnetic resonance: Effects of processing

One‐ and two‐dimensional xenon‐129 nuclear magnetic resonance (¹²⁹Xe NMR) experiments were performed on a series of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PXE) samples to characterize the sorption environments and the relative mobility of xenon in the samples. Samples of PXE in sealed NMR tubes pressurized with xenon were studied as a function of temperature, pressure, and processing. In a dense cast film of PXE, the shift relative to the free gas resonance is smaller than that observed for typical glassy polymers, indicating a higher free volume environment. Solubility rises rapidly as temperature decreases. The lower shift and rapid increase in solubility with decreasing temperature are consistent with a relatively high free volume environment for gas sorption. If PXE is antiplasticized, the shift is slightly larger, the increase in signal intensity with decreasing temperature is smaller, and the line widths are greater. This sample is a better packed glass with less free volume and slower diffusion. Samples of PXE produced by rapid precipitation have broad lines and even lower shifts corresponding to a wide distribution of higher free volume environments. The appearance of two lines at low temperatures is consistent with the presence of a bimodal distribution of environments similar to what has been observed with positron annihilation lifetime spectroscopy. The resonance closest to the free gas resonance is associated with very large free volume elements relative to those of traditional glassy polymers. In two‐dimensional experiments, there is a rapid exchange of xenon by diffusion between the two environments, indicating the close spatial proximity of the environments. Two‐dimensional experiments and one‐dimensional progressive saturation experiments reflect a rapid exchange of xenon between the sorbed state and the free gas resonance for the precipitated samples. At low temperatures, the high field peak exchanges more rapidly with the free gas. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1965–1974, 2002     

Osmotic compressibility in dilute polystyrene‐cyclohexane and polystyrene‐methylcyclohexane solutions: Correlation of polystyrene virial coefficients with solvent quality

Osmotic compressibilities were determined as a function of temperature for solutions of polystyrene in cyclohexane and methylcyclohexane by static light scattering, the measurements extending well below the theta temperature, T = θ. Virial coefficients extracted from the data are compared with literature values obtained by light scattering, membrane osmometry, and phase equilibrium measurements, and successfully correlated over wide ranges of molecular weight, temperature, and solvent quality. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 184–196, 2001     

Thermal-cycling-induced spectral diffusion and thermal barriers in anisole-doped cyclohexane, an unusual multiphase host-guest system

The host-guest system of anisole incorporated into a cyclohexane matrix was investigated in a series of hole-burning experiments. This system is unusual in that cyclohexane can freeze into coexisting solid phases. The hole-burning experiments support the existence of two crystalline phases and one disordered phase. A second surprising characteristic of this system is that the quasi-line absorption features of the spectra appear inverted at low temperature because of unexpected dominance of fluorescence and phosphorescence.     

Effect of cyclic third components on non-deoxygenated RTP and their potential in developing optical thermometer

Effect of five cyclic third components, cyclohexane, methylcyclohexane, perfluorocyclohexane, perfluoromethylcyclohexane and adamantane, on cyclodextrin-induced room-temperature phosphorescence (CD-RTP) of 1-bromonaphthalene is studied. It is found that these five compounds can induce intensive RTP, and the enhancement order is as follows: cyclohexane>adamantane>methylcyclohexane>perfluorocyclohexane>perfluoromethylcyclohexane. Dependence of RTP intensity on temperature of these systems shows the potential application in developing optical thermometer.     

Chemical shifts in methylcyclohexane

In order to determine the effect of a single methyl group on the chemical shifts of protons in a cyclohexane ring, methylcyclohexane-1,2,3,3,5,5,-d₆ has been synthesized. The protons in the 4-position and the 2,6-equatorial protons are not significantly different from those in ring-frozen cyclohexane. The 2,6-axial protons, however, experience an up-field shift of about 15 Hz from the position of the other axial protons. These observations are discussed in terms of the structure of methylcyclohexane.     

A NMR study of phenol self-association. The quasi-chemical approximation

The NMR dilution chemical shifts of phenol in the cyclohexane, methylcyclohexane and carbon tetrachloride solutions at temperatures +10, +20, +40, +50, +60, +70 and +80°C have been interpreted applying the quasi-chemical approximation. The interchange energies for the OH…O bonding and the chemical shifts of hydroxylic protons in associated phenol molecules have been determined and their temperature dependences studied. The obtained results are in good accordance with the equilibrium calculation data.     

Effect of hydrogen bonding on the intramolecular charge transfer fluorescence of 6-dodecanoyl-2-dimethylaminonaphtalene

The effect of hydrogen bonding on the intramolecular charge transfer (ICT) of 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan) in neat and binary solvent mixtures has been investigated by using steady-state and time-resolved spectroscopic techniques. The different features of ICT emission of laurdan in methylcyclohexane–tetrahydrofuran and methylcyclohexane–ethanol are explained by the absence and presence of hydrogen bonded ICT. The presence of isosbestic point in absorption spectra of laurdan in methylcyclohexane–ethanol confirms the formation of 1:1 complex between laurdan and ethanol. The obtained data were used to determine the stoichiometric equilibrium constants. In protic rigid (77 K) the fluorescence spectra of laurdan show excitation wavelength dependence (the red-edge effect). Moreover, we reported the decay characteristics of laurdan molecule in locally excited (LE) and ICT state in methylcyclohexane–ethanol.     

The mechanism of photoionization of malachite green leucocyanide in polar solvents

The fluorescence lifetime and quantum yield of malachite green leucocyanide has been measured in cyclohexane, ethanol and acetonitrile and has been compared with the corresponding values for N,N-dimethylaniline in the same solvents. In cyclohexane, the data is essentially identical, but in polar solvents there are large differences. These are attributed to the fact that the leucocyanide photoionized to malachite green cation from its first excited singlet state.