Thermodynamic properties of the benzene-phenol dimer in dilute aqueous solution

Precise vapor pressure-solubility measurements have been obtained for dilute solutions of benzene and phenol in water at 15, 25, 35 and 45°C. All of the results are consistent with a mass action model that attributes deviations from ideal solution behavior to the formation of benzene dimers and hetero-dimers between benzene and phenol. The benzene-phenol dimer forms endothermically at 25°C, with a very large negative heat capacity, and a formation constant that reaches a maximum value of 0.66 l-mol^?1 at approximately 35°C. Thermodynamic properties of the benzene-phenol dimer are reported and compared with those of other aggregates that are believed to be stabilized primarily by hydrophobic interactions.     

Liquid phase PVT data for binary mixtures of toluene with nitroethane and acetone,and benzene with acetonitrile,nitromethane, and ethanol

Liquid phase PVT data were obtained at 0°C, 45°C, and 90°C for pressures up to 217.7 atm for various binary mixtures of toulene—nitroethane, toluene—acetone, acetonitrile—benzene, nitromethane—benzane, and ethanol—benzene. Such data are required for purposes of converting excess thermodynamic property data from a constant pressure basis to a constant volume basis. Data are presebt for each pure component and for three separate mole fractions for each binary pair. Because benzene solidifies at 5.5°C, data for pure benzene are reported at 12°C rather than 0°C.     

Mischungskalorimetrie mit einem verdrängungskalorimeter,dargestellt an den systemen benzol + n-heptan, 2-methylnaphthalin + 1-methylnaphthalin,toloul + chlorbenzol und chlorbenzol + äthylbenzol

The design of a displacement calorimeter and the methods of measuring positive and negative enthalpies of mixing are described. The calorimeter has been checked by measuring the enthalpies of mixing of benzene + n-heptane and toluene + chlorobenzene at 25°C. Measurements for the systems 2-methylnaphthalene + 1-methylnaphthalene and chlorobenzene + ethylbenzene at 45°C and 25°C, respectively, are reported.     

A solute vapor pressure study of complexes between benzene and caffeine in aqueous solutions

Highly precise vapor pressure-solubility measurements have been obtained for aqueous solutions of caffeine at temperatures in the range 15 to 45°C. Values of the fugacity of benzene at known total concentrations of benzene and caffeine have been calculated and used to derive equilibrium constants for the interaction of benzene molecules with monomers and aggregates of caffeine. Data are quite precisely represented by a mass action model in which benzene attaches to associated caffeine species with a binding constant that increases in direct proportion to the molecular weight of the caffeine aggregate. An equilibrium constant for the reaction benzene monomer+caffeine monomer-benzene·caffeine is reported at each temperature. The role of hydrophobic association effects in stabilizing the various complexes is considered.     

Thermodynamic functions for the systems 1-butanol, 2-butanol,andt-butanol + cyclohexane

The following properties of mixtures of the butanols with cyclohexane were measured over the whole range of composition: 1-butanol+cyclohexane and 2-butanol+cyclohexane; excess enthalpies at 15, 25, 35 and 45°C, excess volumes at 25 and 45°C, activity coefficients and excess Gibbs free energies at 45°C. 2-Methylpropan-2-ol (tertiary butanol)+cyclohexane; excess enthalpies at 26, 35, and 45°C, excess volumes at 26 and 45°C, activity coefficients and excess Gibbs free energies at 45°C. From these data, activity coefficients at the temperatures of the excess enthalpy measurements below 45°C have been computed, as a source of test data for models of alcohol association through hydrogen bonding.     

Poly(N-n-butylitaconimide). Preparation and characterization

Poly(N-n-butylitaconimide) was prepared by radical polymerization in benzene and in bulk at 60°C and was subsequently fractionated at 30°C with benzene and methanol as solvent and nonsolvent, respectively. Relationships between molecular weight and intrinsic viscosity (Mark-Houwink-Sakurada equations) in tetrahydrofuran, benzene, and toluene at 30°C are established. From the Burchard-Stockmayer-Fixman plot, the characteristic ratio of this polymer is determined, and local chain conformation is discussed in relation to the termination process in radical polymerization. © 1993 John Wiley & Sons, Inc.     

High surface area MoO3/TiO2 hydrodesulfurization catalysts

The catalytic combustion of benzene over SBA-15-supported copper oxide has been investigated. The SBA-15-supported copper oxide catalysts have been prepared by the precipitation-deposition method, and characterized by XRD, BET and TPR. In the CuO/SBA-15 catalysts, the catalytic activity increases with increasing copper oxide loading ratio. Metallic Cu is much more active than copper oxides. When the reduction temperature increases to 500°C the benzene conversion increases until the maximum vlaue is obtained. Further increase in the reduction temperature to 600°C results in a decrease of benzene conversion.     

Kinetic Modeling of Esterification Reaction of Surfactin-C15 in Methanol Solution

Surfactin in methanol solution with acid would be spontaneously esterified into the mono- or dimethyl ester surfactin even at a temperature as low as 4 °C because there were two free carboxyl groups in the peptide loop of surfactin. Using trifluoroacetic acid as the catalyst, the esterification and the contents change in surfactin-C₁₅, mono- and dimethyl ester surfactin-C₁₅ with time were investigated at 4, 25, and 45 °C, respectively. The kinetic model was established for prediction of the esterification degree under experimental conditions. At 4, 25, and 45 °C, more than 10 % of the surfactin-C₁₅ in methanol solution in the presence of 0.05 % trifluoroacetic acid was changed into the esterified surfactin-C₁₅ after 37.6, 14.1, and 7.4 h, respectively. The maximum of intermediate of the mono-methyl ester surfactin-C₁₅ was observed at 4, 25, and 45 °C after 25, 10, and 5 days, respectively. Our results indicated that the time for preparation should be strictly controlled to avoid an unexpected esterification of surfactin during its storage and experimental treatment, and the kinetic results could be adopted as the reference condition for preparation of monomethyl ester surfactin-C₁₅.     

Catalytic hydrogenation on Raney nickel of estra-1,3,5(10),8,14-pentaenes with sterically accessible double bonds

The catalytic hydrogenation of estra-1,3,5(10),8,14-pentaenes with sterically accessible double bonds in the presence of Raney nickel in 2-propanol at elevated pressure and at heating to 110–120°C resulted in prevailing formation of estrogens 8α-analogs alongside a considerable quantity of estra-5,7,9-trienes. Although the hydrogenation at 45–60°C provided a higher yield of estrogens 8α-analogs, the synthesis of steroids of this group gave better results at hydrogenation in a high purity benzene.     

Thermodynamic properties of some concentrated polymer solutions

Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor-pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt-%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.     

Measurement of vapor-liquid equilibrium in systems with components of very different volatility by the total pressure static method

To make feasible the experimental study of vapor-liquid equilibrium (VLE) in the systems mentioned in the title, a static apparatus for accurate measurement of total vapor pressures of solutions was constructed. Mixtures of known composition are prepared synthetically in a thermostated equilibrium cell by weight from pure degassed components and the total pressure is measured by a quartz Bourdon gage. A procedure was developed for degassing pure liquids to a degree corresponding to the high precision of pressure determination required. The static assembly was tested by comparing obtained isothermal vapor pressures and calculated excess Gibbs free energies with literature data for the benzene - cyclohexane system at 14 and 20°C, respectively. Additional experimental vapor-pressure data are presented for pure cyclohexane, benzene, and N-methylpyrrolidone (abbreviated throughout this paper as NMP) at 6–24°C and for the binary systems of benzene-cyclohexane at 8°C and cyclohexane - NMP and benzene - NMP at 8, 14, and 20°C over the entire composition range. The binary data were reduced by a modified Barker's method to evaluate excess Gibbs free energies and vapor phase compositions.     

Die durch Silberionen katalysierte Umlagerung von Propargyl-phenyläther

It is known that propargyl-phenylethers rearrange at about 200° to 2 H-chromenes [1–4]. It is shown that this rearrangement occurs in benzene or chloroform at lower temperatures (20–80°) in the presence of silver-tetrafluoroborate (or-trifluoracetate). The ethers examined are presented in Scheme 1. Thus in chloroform at 61° in the presence of AgBF₄, phenyl-propargylether ( 3 ) yields 2 H-chromene ( 13 ). With 0.78 molar equivalents AgBF₄ in benzene at 80° the same ether 3 yields a 3:1 mixture of 2-methyl-cumaron ( 14 ) and 2 H-chromene ( 13 ). From 1′-methylpropargyl-phenylether ( 4 ) and 2′-butinyl-3,5-dimethylphenylether ( 5 ) under similar conditions the corresponding chromenes 16 and 17 resp. are obtained. Rearrangement of propargyl- and 2′-butinyl-1-methyl-2-naphthylether ( 6 and 7 resp.) in benzene at 80° in the presence of AgBF₄ gives the corresponding allenyl-naphthalenones 18 and 19 resp. Treatment of propargyl- and 2′-butinyl-mesityl-ether ( 8 and 9 resp.), and propargyl- and l′-methylpropargyl- 2 , 6 -dimethyl-phenylether ( 10 and 11 resp.) in benzene at 80° with AgRF, yields as the only product the corresponding 3 -allenyl-phenols 21 , 22 , 24 and 25 (Scheme 3). It is shown that in the presence of μ-dichlor-dirhodiuni (1)-tetracarbonyl in benzene a t 80° the ether 4 rearranges to 2-methyl-2H-chromene (16). However with this catalyst the predominant reaction is a cleavage to phenol. No reaction was observed when ethers 3 and 12 , (Scheme 7 ) were treated with the tris-(trimethylsily1)-ester of vanadic acid in benzene a t 80° (see also [8]). By analogy with the known mechanism for thc silver catalysis of the reversible propargylesterl/allenylester rearrangement [S], the silver (1)ion is assumed to form a pre-equilibrium π-complex with the C, C-triplebond of the substrate. This complex then undergoes a [3s, 3s]-sigmatropic rearrangement (Scheme 2). In the case of the others 6 , 7 and 12 the resulting allenyldienones were isolated. The 2,G-dimethyl substituted ethers 8 , 9 , 10 and 11 resp. first give the usual allenyl- dienones (Scheme 3). These then undergo a novel silver catalysed dienon-phenol-rearrangement (Sclzenzu4) to give the 3-allenylphenols 21 , 22 , 24 and 25 . Thc others 3 , 4 and 5 with free ortho positions presumably rearrange first to the non-isolated 2-allenyl-phenols 15 , 42 and 43 resp.(Scheme 7). These then rearrange, either thermally or by silver (1)ion catalysis to the 2H-chromenes 13 , 16 and 17 resp. The rate of the rearrangement of 2-allenylphenol ( 15 ) to 13 at room temperature in benzene or chloroform is approximately doubled when silver ions are present as catalyst.     

3‐[4′‐(Diethylboryl)phenyl]pyridine: Exclusive Crystallization of the Cyclic Tetramer

The crystallization of 3‐[4′‐(diethylboryl)phenyl]pyridine ( 1 ), which formed a mixture of oligomers in solution with the cyclic trimer as a major component, in acetone at 0 °C afforded a cyclic tetramer that co‐crystallized with solvent molecules. Similarly, solutions of compound 1 in toluene at 10 °C and in benzene at 8 °C furnished the cyclic tetramer with the incorporation of toluene and benzene molecules, respectively, thus suggesting that the cyclic tetramer was the minor component. ¹³C CP/MAS NMR spectroscopy of precipitates of compound 1 suggested that precipitation from acetone and toluene each afforded mixtures of the cyclic trimer and the cyclic tetramer, whereas precipitation from benzene exclusively furnished the cyclic tetramer. Therefore, it appeared that crystallization readily shifted the equilibrium towards the cyclic tetramer in benzene. The thermodynamic parameters for the equilibrium between these two oligomers in [D₆]benzene, as determined from a van′t Hoff plot, were ΔH°=?8.8 kcal mol^?1 and ΔS°=?23.7 cal mol^?1 K^?1, which were coincident with previously reported calculations and observations.     

Thermal degradation of aramids: Part I—Pyrolysis/gas chromatography/mass spectrometry of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of poly(1,3-phenylene isophthalamide) or Nomex (I) and poly(1,4-phenylene terephthalamide) or Kevlar (II) aramids have been investigated in the temperature range 300–700°C by pyrolysis/gas chromatography/mass spectrometry. The initial degradation products below 400°C of (I) are carbon dioxide and water. At 400°C benzoic acid and 1,3-phenylenediamine are detected. Benzonitrile, aniline, benzanilide, N-(3-aminophenyl)benzamide as well as carbon monoxide and benzene are evolved in the range 430–450°C. The yields of these products increase rapidly in the range 450–550°C. Isophthalonitrile is observed at 475°C and hydrogen cyanide is detected above 550°C, as are other secondary products such as toluene, tolunitrile, biphenyl, 3-cyanobiphenyl and 3-aminobiphenyl. Pyrolysis of (II) below 500°C evolves only water and trace amounts of carbon dioxide. At 520–540°C the following degradation products have been detected: 1,4-phenylenediamine, benzonitrile, aniline, benzanilide and N-(4-aminophenyl)benzamide. These products as well as carbon dioxide and water increase appreciably between 550°C and 580°C; benzoic acid, terephthalonitrile, benzene and 4-cyanoaniline are also detected in this temperature range. Above 590°C, hydrogen, carbon monoxide, hydrogen cyanide, toluene, tolunitrile, biphenyl, 4-aminobiphenyl and 4-cyanobiphenyl are evolved. Degradation reactions consistent with the formation of these products, which involve initial heterolytic cleavage of the amide linkage for (I) and initial homolytic cleavage of the aromatic NH and amide bonds for (II), are described.     

A dipole moment study of the conformational properties of diaryl diselenides and related compounds

The electric dipole moments of the diaryl diselenides (RC₆H₄)₂Se₂ (R  H, 4-F, 4-Br, 4-CH₃, 3-F) were measured in benzene solution at 25 and 45°C. The conformations of these compounds were deduced by matching experimental moments with values calculated for a variety of possible conformations. In the dissolved state the diselenides exist at 25°C in fixed “skew” conformations characterized by dihedral angles of 75–106° between the CSeSe planes, corresponding to the conformational energy minima. At 45°C oscillations about the SeSe bonds are excited in the diphenyl and bis(4-methylphenyl) diselenides, whereas the 4-bromophenyl derivative exhibits free rotation. The fluoro compounds have temperature-independent dipole moments, suggesting “rigid conformations” with dihedral angles of 106° (4-F) and 74.4° (3-F). An analysis of the dipole moments at 25 and 45°C obtained for the compounds (RC₆H₄)₂X₂ (R  H, 3-F, 4-F, 4-Br, 4-CH₃; X  S, Se, Te) showed that the conformational properties of these derivatives change on passing from X  S to X  Te. The observed variations are explicable in terms of a decreasing repulsion between the lone electron pairs of the chalcogen atoms on going from the disulfides to the ditellurides and a concomitant reduction of the energy barrier to rotations about the XX bonds.     

X‐ray crystallographic analysis and differential scanning calorimetry of two polymorphic forms of 2,6‐diphenyl‐1,4‐dithiin

2,6‐Diphenyl‐1,4‐dithiin 2 exists in the two polymorphic forms. The dithiin 2L , mp 62–63°C, was assigned as the metastable form, while the dithiin 2H , mp 79–80°C, was assigned as the stable form, mainly on the basis of differential scanning calorimetry (DSC) analysis. X‐Ray crystallographic analysis showed that the largest difference in the molecular structure between 2L and 2H is found in the coplanarity between the benzene ring and the double bond part of the dithiin ring; the benzene ring and the double bond are nearly coplanar for 2L , whereas these are far from being coplanar for 2H . © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:424–427, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20035     

Thermostability of polymers containing indanic units in the main chain

The acid-catalyzed stepwise polymerization of 1,1-diphenylethylene derivatives, p-di(1-phenylvinyl) benzene, bis[p-(1-phenylvinyl)phenyl]methane, 1,2-bis[p-(1-phenylvinyl)phenyl]ethane, bis[p-(1-phenylvinyl)phenyl]ether, and bis[p-(1-phenylvinyl)phenyl]sulfide produced selectively indanic-unit-containing polymers in pertinent conditions. Their molecular weights (M?_n) were in the 1600–15, 700 region after the fractionation in hot ethnol. Melting points were in the 214–281°C region. They dissolved fairly well in conventional solvents like benzene, tetrahydrofuran, and carbon tetrachloride. According to TGA they started to decompose at 397–432°C and showed 10% weight loss at 478–502°C in air at a heating rate of 5°C/min. Focusing on the thermostability, we report on their physical properties.     

Synthesis and thermal stability of the resins prepared from the reactions of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines and electrical conductivity of the resulting materials following pyrolysis

New thermosetting resins were prepared from the reaction of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines in varying molar ratios. The thermal stability of these resins was correlated with their composition and the curing conditions. They were stable in N₂ up to 370–448°C and afforded anaerobic char yields of 73–84% at 800°C after curing at 300°C for 20–60 h. The temperature dependence of the electrical resistivity of all resins pyrolyzed at 700°C for 15 h was studied in the temperature range from ?173–327°C (100–600 K). The results showed that at room temperature the unpyrolyzed polymers have insulating properties, whereas a dramatic decrease in the electrical resistivity is observed following pyrolysis. The temperature dependence of the electrical resistivity suggests that all of the materials studied have semiconducting properties. The observed electrical conductivity is thermally activated with activation energies ranging from 0.03–0.06 eV. © 1994 John Wiley & Sons, Inc.     

Interfacial sythesis of polyphosphonate and polyphosphate ester. VII. Temperature effects and reaction loci in polycondensations of hydroquinone with phenylphosphonic dichloride and 4-methythiophenyl phosphorodichloridate

Polyphosphate and polyphosphonate esters of molecular weights > 10,000 were synthesized by base-promoted, liquid-vapor and liquid-liquid interfacial polycondensations of hydroquinone (HQ) with 4-methylthiophenyl phosphorodichloridate (MTPP) and phenylphosphonic dichloride (PPD). The barium hydroxide-initiated liquid-vapor polycondensation of PPD and HQ in the temperature range of 15–95°C shows that [η] increases with reaction temperature and unfractionated yields exhibit a maximum at about 45°C. The analogous liquid-vapor polycondensation of MTPP and HQ between 25 and 85⁴C also shows a maximum yield at 45°C, whereas [η] decreases with increase in reaction temperature. The results are contrasted with temperature dependencies of base-catalyzed, liquid-liquid polycondensation of HQ with MTPP and PPD. A different insight is obtained by analyzing the temperature effects on fractionated products. The relative importance of degradative saponification reactions are ranked as attack on chain ester linkages > phosphorus chloride reactant > end groups of growing chains.