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Totally found 199 items.

  • [会议] Kinetics and mechanism of the reaction of coherently synchronized oxidation and dehydrogenation of cyclohexane by hydrogen peroxide
    Inducing effect of hydrogen peroxide on synchronous oxidation reaction is accompanied by the occurrence of two interconnected and interacting reactions. The reaction of H2O2 decomposition (primary) generates the leading active OHandHO2 free radicals in a system. During the interaction of active and free radicals with the substrate, the conversion of the substrate occurs in the secondary reaction, coherently-synchronized with the primary one. The mechanism of such coherently synchronized reactions is being examined in the process of cyclohexane oxidation with hydrogen peroxide in homogeneous and heterogeneous systems. The process of coupling dehydrogenation of cyclohexane to cyclohexene and cyclohexadiene with hydrogen peroxide was carried out without catalyst. This process was also carried out at a fairly low temperature in a heterogeneous catalytic system. Biomimetic catalyst, which simulates the basic functions of the enzyme group of oxidoreductase-catalase and monooxygenase, was used as the catalyst here. Characterised by its highly active and selective action these biomimetic catalysts are synthesized based on iron-porphyrin complexes simulating the active component of cytochrome P-450. Based on this experimental researches, the complex reaction, consisting of parallel-sequential oxidation and dehydrogenation reactions, which are coherently synchronized, proceeds during the process of cyclohexane oxidation with biomimetic catalyst. Depending on the reaction parameters it is possible to deliberately adjust the direction of oxidation reaction and reaction rate.
    关键词: Oxidation (major);Biomimetic processes;Biomimetics;Catalysts;Cyclohexane;Dehydrogenation;Free radicals;Hydrogen;Hydrogen peroxide;Peroxides;Reaction kinetics;Synchronization;Synthesis (chemical);Temperature
  • [会议] Cholesteric cyclohexane-Containing Side-Chain Liquid-Crystalline Polysiloxanes
    Two new kinds of Cholesteric cyclohexaneContaining Side-Chain Liquid-Crystalline Polysiloxanes(PA and PB)were synthesized via hydrosilylation reaction of polymethyl hydrogen siloxane with cyclo-hexane mesogenic monomers(MA and MB).The yield of PA,PB were 71.6%,82.5%and 81.0%,respectively.The molecular structures of MA and MB,PA and PB were investigated by Fourier transform infrared spectroscopy(FTIR)and hydrogen-nuclear magnetic resonance spectra(1H-NMR).The corresponding liquid crystalline phase type was also observed by polarizing optical microscopy(POM)and Xray diffraction(XRD).The liquid crystalline phase behavior and thermal properties of the polymers were analyzed by differential scanning calorimetry(DSC).Results showed that MA and MBexhibited multicolor platelet texture of a blue phase and cholesteric phase,and the Tm and Ti of MA and MBincreased with the increasing flexible chain length.The mesophase temperature range of PA and PB was broader than that of MA and MB.PAexhibited a rare nematic phase——spherulite texture of polymeric smectic A phase.PBwere of cholesteric and nematic——cholesteric phase.The Tm and Ti of PA and PB increased with the increasing flexible spacer groups.
    关键词: Polysiloxanes;Liquid crystalline polymer;Cholesteric phase;smectic A phase
  • [会议] Chiral Cyclohexane-1,2-Bridged Bis-NHC-Palladium Catalysts for Asymmetric Suzuki-Miyaura Coupling Reactions
    Axially chiral biaryls are common structure motifs in natural products and are the core for many of the most effective chiral ligands,such as the well-known BINAP,MOP and BINOL ligands.The palladium-catalyzed asymmetric Suzuki-Miyaura coupling has recently emerged as an attractive alternative to standard methods for the control of biaryl axial chirality.~1 One of the challenges is to find suitable chiral ligands to support catalysts that are able to induce high levels of enantioselectivities.~2
    关键词: Suzuki;Palladium;chiral;palladium;attractive;catalyzed;asymmetric;challenges;emerged;cyclohexane
  • [会议] Experimental Study on Hydrodynamic Characteristics of Cyclohexane at Trans- and Supercritical Pressures
    As an effective cooling method, the regenerative cooling technology using hydrocarbon fuel as coolant has been studied extensively in aircraft and space vehicles. Static flow instability, which is caused by multi-valued of hydrodynamic characteristics, often occurs under certain conditions affecting on the convection heat transfer process. The hydrodynamic characteristics of hydrocarbons naturally is attracted more attention on the regenerative cooling technology. In this paper, an experimental study on hydrodynamic characteristics of cyclohexane has been conducted at pressures ranging from 2.5 to 5.5 MPa, inlet temperature from 30.0 to 100.0℃ and heat flux from 95 to 205 kW/m~2. Some hydrodynamic characteristics curves are obtained in a horizontal stainless steel tube with 2.0 mm hydraulic diameter. In these experiments, the multi-valued characteristics of hydrodynamic characteristics curves existed for hydrocarbons were well-proved at trans-and supercritical pressures. Onset of the negative slope area of hydrodynamic characteristics was found when the fluid outlet temperature became slightly lower than its respective pseudo-critical temperature. And, the multi-valued tendency of test fluid was weakened with the increase of pressure and inlet temperature, however enhanced as the heat flux increased. Based on the experimental data, a formula for determining the onset of flow instability for cyclohexane was finally summed for the supercritical fluid.
    关键词: multi-valued;hydrodynamic;finally
  • [会议] Associations of Maternal Pregnancy Urine Estrogen Levels with Phthalate and Phthalate Replacement (1,2-Cyclohexane Dicarboxylic Acid Diisononyl Ester, DiNCH) Metabolites
    Rationale: Pregnant women are exposed to phthalates in food, personal care and household products. Phthalates alter estrogen levels in experimental models but their potential to impact levels in human pregnancy is not well characterized. Methods: 291 participants in an Illinois pregnancy cohort collected 5 urines across pregnancy for pooling and quantification of 16 phthalate/DiNCH metabolites. Exposures were expressed as the molar sum of metabolites for: ΣDiNCH, ΣDEHP, ΣDBP, ΣDiBP, ΣDiNP, ΣPCP, and ΣAA (respective personal care product and anti-androgenic phthalates). At 10-14, 28-30 and 34-36 gestational weeks (GW), urine estradiol, estrone, estriol and metabolites were measured and summed (ΣE). Specific gravity adjusted exposure and ΣE data were log-transformed. Linear mixed-effects models assessed relationships of phthalates/ΣDiNCH with ΣE controlling for fetal sex, maternal age, prepregnancy BMI, ΣE analytic batch, and GA at urine collection for ΣE evaluation. Interactions of phthalates/ΣDiNCH, fetal sex, ΣE batch, and GA at ΣE urine collection were explored. Results: Participants were 82% white, 72% had income >$60,000/yr, 84% had a college+ education, and urine biomarker levels were similar to U.S. women. At 10-14 weeks, ΣE increased with increasing: ΣDBP (b=1.5, 95% CI=0.5, 2.5), ΣDiNP (b=1.3, 95% CI=0.6, 2.0), ΣPCP (b=0.S, 95% CI=0.1, 0.8), and ΣAA (b=0.4, 95% CI=0.01, 0.7); associations in late pregnancy were attenuated and non-significant. ΣE increased with increasing ΣDEHP in women carrying females (b=0.7, 95% CI=0.2, 1.3) and ΣDiBP in women carrying males for ΣE measured in only one analytic batch. ΣE was not associated with ΣDiNCH. Conclusions: ΣDBP, ΣDiNP, ΣPCP, and ΣAA phthalates were associated with higher gestational ΣE in early but not later pregnancy. For other phthalates, associations were only in small sub-group analyses. Whether pregnancy estrogen levels mediate associations between phthalates and pregnancy outcomes merits investigation.
    关键词: -
  • [会议] Thermo-acoustical properties of 1,1'-bis(2,6-dichloro-4-hydroxyphenyl) cyclohexane solutions at atmospheric pressure
    In present work we have reported thermo-acoustical and thermodynamic properties of 1,1'-Bis(2,6-dichloro-4-hydroxyphenyl)cyclohexane(Cl BC). The density(ρ), viscosity(η) and ultrasonic speed(U) of pure solvents [1, 4-dioxane(DO), chloroform(CF), ethylacetate(EA), tetrahydrofuran(THF)] andCl BC solutions were investigated at four different temperatures: 298, 303, 308 and 313 K to understand the effect of solvents and temperature on molecular interactions. Various acoustical and thermodynamic parameters such as specific acoustical impedance(Z), adiabatic compressibility( a), intermolecular free path length(L f), Rao's molar sound function(R m), Van der Waals constant(b), internal pressure(π), free volume(V f), viscous relaxation time(τ) and classical absorption coefficient(α/f 2)cl were calculated and fairly good co-relationship between calculated parameters were obtained. A fairly good to excellent correlation between a given parameter and concentration is observed at all temperatures and solvent systems studied. Gibb's free energy of activation(?G*) is found both concentration and temperature dependent. Both enthalpy of activation(?H*) and entropy of activation(?S*) are found concentration dependent. Thus, acoustical and thermodynamic parameters confirmed presence of strong molecular interactions and structure making nature of the compound.
    关键词: Density;viscosity;ultrasonic speed;acoustical parameters;thermodynamic parameters;molecular interactions
  • [会议] Experimental Study on Hydrodynamic Characteristics of Cyclohexane at Trans- and Supercritical Pressures
    As an effective cooling method, the regenerative cooling technology using hydrocarbon fuel as coolant has been studied extensively in aircraft and space vehicles. Static flow instability, which is caused by multi-valued of hydrodynamic characteristics, often occurs under certain conditions affecting on the convection heat transfer process. The hydrodynamic characteristics of hydrocarbons naturally is attracted more attention on the regenerative cooling technology. In this paper, an experimental study on hydrodynamic characteristics of cyclohexane has been conducted at pressures ranging from 2.5 to 5.5 MPa, inlet temperature from 30.0 to 100.0℃ and heat flux from 95 to 205 kW/m~2. Some hydrodynamic characteristics curves are obtained in a horizontal stainless steel tube with 2.0 mm hydraulic diameter. In these experiments, the multi-valued characteristics of hydrodynamic characteristics curves existed for hydrocarbons were well-proved at trans-and supercritical pressures. Onset of the negative slope area of hydrodynamic characteristics was found when the fluid outlet temperature became slightly lower than its respective pseudo-critical temperature. And, the multi-valued tendency of test fluid was weakened with the increase of pressure and inlet temperature, however enhanced as the heat flux increased. Based on the experimental data, a formula for determining the onset of flow instability for cyclohexane was finally summed for the supercritical fluid.
    关键词: multi-valued;hydrodynamic;finally
  • [会议] Benzene and cyclohexane separation using 1-butyl-3-methylimidazolium thiocyanate
    Cyclohexane is mainly produced by catalytic hydrogenation of benzene. Removal of unreacted benzene from the product stream is very important in this process. However, due to their close boiling points and azeotrope formation, it is very difficult to separate cyclohexane and benzene by conventional distillation. Currently, special separation processes such as processes extractive distillation is commercially used for this separation. However, this extractive distillation suffers from process complexity and higher energy consumption due to their low extractive selectivity of molecular entrainers used. The aim of the present work is to investigate the applicability of ionic liquids as entrainer in extractive distillation of benzene and cyclohexane mixture. In this study, we investigated 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) ionic liquid for separation of benzene and cyclohexane by measuring the Vapor Liquid Equilibrium data of the two components in the presence of the ionic liquid. As green and potential environmentally friendly solvents, ionic liquids have attracted increasing attention as alternative conventional entrainers in extractive distillation. Isothermal Vapor Liquid Equilibrium for the benzene + cyclohexane + [BMIM][SCN] ternary system was obtained at 353.15 K using a Head Space Gas Chromatography. The addition of [BMIM][SCN] breaks the benzene-cyclohexane azeotrope and increased the relative volatility cyclohexane to benzene in the mixture. The effect of [BMIM][SCN] on the relative volatility cyclohexane to benzene was studied at various benzene and cyclohexane compositions and solvent to feed ratios. The performance of [BMIM][SCN] was compared with typical conventional solvents, dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The results show that the relative volatility of cyclohexane to benzene in the presence of [BMIM][SCN] is higher compared that of DMSO and DMF. J. P. Garcia Villaluenga, A. Tabe-Mohammadi, A review on the separation of benzene/cyclohexane mixtures by pervaporation processes. Journal of Membrane Science. 169 (2000) 10.1016/S0376-7388(99)00337-3 K. Weissermel, H. J. Arpe Industrial organic chemistry. third ed. (Verlagsgesellschaft mbH, Wenham, 1997) 10.1002/9783527616688 W. S. Johnson Johnson, V. J. Bauer, J. L. Margrave, M. A. Frisch, L. H. Dreger, W. N. Hubbard, The Energy Difference between the Chair and Boat Forms of Cyclohexane. The Twist Conformation of Cyclohexane. Journal of the American Chemical Society. 83 3 (1961) 10.1021/ja01464a027 S. J. Lue, F. J. Wang, S. Y. Hsiaw, Pervaporation of benzene/cyclohexane mixtures using ion-exchange membrane containing copper ions. Journal of Membrane Science. 240 1 (2004) 10.1016/j.memsci.2004.05.003 H. Dong, X. Yang, J. Zhang, Liquid–Liquid Equilibria for Benzene + Cyclohexane + N, N-Dimethylformamide + Potassium Thiocyanate. Journal of Chemical &Engineering Data. 55 9 (2010) 10.1021/je100036x X. K. Wang, M. Tian, Separating benzene-cyclohexane by extractive distillation with salt. Chemical Engineering (China). 37 3 (2009) H. Dong, X. Yang, G. Yue, W. Cao, J. Zhang, Liquid–Liquid Equilibria for Benzene + Cyclohexane + N,N-Dimethylformamide + Ammonium Thiocyanate. Journal of Chemical &Engineering Data. 56 5 (2011) 10.1021/je1012026 Z. Lei, B. Chen, Z. Ding Special distillation processes. First Ed. (Elsevier Science, Amsterdam, 2005) J. Chen, Z. Li, L. Duan, Liquid–Liquid Equilibria of Ternary and Quaternary Systems Including Cyclohexane, 1-Heptene, Benzene, Toluene, and Sulfolane at 298.15 K. Journal of Chemical &Engineering Data. 45 4 (2000) 10.1021/je990331v
    关键词: chromatography;distillation;mixtures;separation;solvents (industrial)
  • [会议] Thermo-acoustical properties of 1,1'-bis(2,6-dichloro-4-hydroxyphenyl) cyclohexane solutions at atmospheric pressure
    In present work we have reported thermo-acoustical and thermodynamic properties of 1,1'-Bis(2,6-dichloro-4-hydroxyphenyl)cyclohexane(Cl BC). The density(ρ), viscosity(η) and ultrasonic speed(U) of pure solvents [1, 4-dioxane(DO),chloroform(CF), ethylacetate(EA), tetrahydrofuran(THF)] and Cl BC solutions were investigated at four different temperatures: 298, 303, 308 and 313 K to understand the effect of solvents and temperature on molecular interactions. Various acoustical and thermodynamic parameters such as specific acoustical impedance(Z), adiabatic compressibility( a), intermolecular free path length(Lf), Rao's molar sound function(Rm), Van der Waals constant(b), internal pressure(π), free volume(Vf), viscous relaxation time(τ) and classical absorption coefficient(α/f 2)cl were calculated and fairly good co-relationship between calculated parameters were obtained. A fairly good to excellent correlation between a given parameter and concentration is observed at all temperatures and solvent systems studied. Gibb's free energy of activation(?G*) is found both concentration and temperature dependent. Both enthalpy of activation(?H*) and entropy of activation(?S*) are found concentration dependent. Thus, acoustical and thermodynamic parameters confirmed presence of strong molecular interactions and structure making nature of the compound.
    关键词: Density;viscosity;ultrasonic speed;acoustical parameters;thermodynamic parameters;molecular interactions
  • [会议] Associations of Maternal Pregnancy Urine Estrogen Levels with Phthalate and Phthalate Replacement (1,2-Cyclohexane Dicarboxylic Acid Diisononyl Ester, DiNCH) Metabolites
    Rationale: Pregnant women are exposed to phthalates in food, personal care and household products. Phthalates alter estrogen levels in experimental models but their potential to impact levels in human pregnancy is not well characterized. Methods: 291 participants in an Illinois pregnancy cohort collected 5 urines across pregnancy for pooling and quantification of 16 phthalate/DiNCH metabolites. Exposures were expressed as the molar sum of metabolites for: ΣDiNCH, ΣDEHP, ΣDBP, ΣDiBP, ΣDiNP, ΣPCP, and ΣAA (respective personal care product and anti-androgenic phthalates). At 10-14, 28-30 and 34-36 gestational weeks (GW), urine estradiol, estrone, estriol and metabolites were measured and summed (ΣE). Specific gravity adjusted exposure and ZE data were log-transformed. Linear mixed-effects models assessed relationships of phthalates/ΣDiNCH with ΣE controlling for fetal sex, maternal age, pre-pregnancy BMI, ΣE analytic batch, and GA at urine collection for ΣE evaluation. Interactions of phthalates/ΣDiNCH, fetal sex, ΣE batch, and GA at ZE urine collection were explored. Results: Participants were 82% white, 72% had income >$60,000/yr, 84% had a college+ education, and urine biomarker levels were similar to U.S. women. At 10-14 weeks, ZE increased with increasing: ΣDBP (b=1.5, 95% Cl=0.5, 2.5), ΣDiNP (b=1.3, 95% Cl=0.6, 2.0), ΣPCP (b=0.5, 95% Cl=0.1, 0.8), and ΣAA (b=0.4, 95% Cl=0.01, 0.7); associations in late pregnancy were attenuated and non-significant. ΣE increased with increasing ΣDEHP in women carrying females (b=0.7, 95% Cl=0.2, 1.3) and ΣDiBP in women carrying males for ΣE measured in only one analytic batch. ΣE was not associated with ΣDiNCH. Conclusions: ΣDBP, ΣDiNP, ΣPCP, and ΣAA phthalates were associated with higher gestational ΣE in early but not later pregnancy. For other phthalates, associations were only in small sub-group analyses. Whether pregnancy estrogen levels mediate associations between phthalates and pregnancy outcomes merits investigation.
    关键词: -
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