Vapor pressure studies of hydrophobic association. Thermodynamics of fluorobenzene in dilute aqueous solution

An automated vapor pressure apparatus has been used to obtain measurements of the vapor pressure of aqueous solutions of fluorobenzene at temperatures of 15, 25, 35, and 45°C, and in the concentration range 0 to 0.011M. The results have been interpreted to infer the dimerization constant of fluorobenzene in very dilute aqueous solutions, equivalent to the second virial coefficient of interaction between fluorobenzene molecules. The hydrophobic association of fluorobenzene molecules is thermodynamically quite similar to that of benzene at comparable temperatures and concentrations. A dimerization constant of fluorobenzene of 0.56 M^–1 at 30°C and an endothermic enthalpy of association equal to 3.9 kcal-mol^–1 are calculated from the measurements.     

Catalytic oxidation of fluorobenzene by molecular oxygen

Kinetic and thermal-desorption methods have been applied to the oxidation of fluorobenzene by molecular oxygen. The catalytic oxidation mechanism for fluorobenzene is similar to that for benzene. A suggestion is made on why there is no fluoromaleic anhydride in the oxidation products from fluorobenzene.Translated from, Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 116–119, January–February, 1989.     

Toxicity （-lgEC50） Measurement of the Fluorobenzene Derivants against Vibrio Qinghaiensis （Q67） and Their 2D,3D-QSAR Study

Toxicities (-lgEC50) of 16 fluorobenzene derivants against vibrio qinghaiensis (Q67) were measured systematically,and their quantum chemistry parameters were calculated at the B3LYP/6-311G** level. Based on the experimental toxicity data and quantum chemistry parameters,2D-QSAR model was proposed,which was validated by variance inflation factors (VIF),t-value and cross-validation method. At the mean time,comparative molecular force field (CoMFA) based on molecular simulation was used to investigate the toxicity of fluorobenzene derivants. Furthermore,the intoxicating mechanism of fluorobenzene derivants was discussed. To our interest,2D-QSAR and CoMFA models exhibit good prediction ability,with which the toxicity of similar compounds can be predicted. Finally,toxicities (-lgEC50) of 12 fluorobenzene derivants against vibrio qinghaiensis (Q67) were predicted with these models.     

Molecular Pair Analysis: C?H⋅⋅⋅F Interactions in the Crystal Structure of Fluorobenzene? And Related Matters

The crystal structure of fluorobenzene is compared with isomorphous crystal structures of molecules of roughly similar shape. The lowest-energy fluorobenzene dimers are identified by theoretical calculations. Molecular pair analysis of the crystal structure of fluorobenzene and of an isomorphous virtual low-energy polymorph of benzene suggests that the important intermolecular interactions in the two structures are closely similar. In particular, the intermolecular C-H...F interactions in the fluorobenzene crystal have approximately the same structure-directing ability and influence on the intermolecular energy as the corresponding C-H...H interactions in benzene. Molecular pair analysis of the isomorphous crystal structures of benzonitrile, alloxan, and cyclopentene-1,2,3-trione indicates that essentially the same crystal structure can be adopted with quite different patterns of pair energies and atom-atom interactions. The question as to whether the packing radius of organic fluorine is larger or smaller than that of hydrogen, is addressed, but not answered.     

Kinetics of the reaction of solvated electrons with fluorobenzene in liquid ammonia

The rate of disappearance of solvated electrons by reaction with fluorobenzene in ammonia is accelerated by small concentrations of methanol; it also has a “negative activation energy” depending on the methanol concentration. The kinetic data suggest an exothermic electron attachment-detachment equilibrium with the fluorobenzene followed by a slower reaction of the electron adduct with the proton donating methanol.     

Densities and Volumetric Properties of Binary and Ternary Mixtures of Diisopropyl Ether, Fluorobenzene, α,α,α-Trifluorotoluene, and Ethanol at Temperature 298.15 K and Pressure 101 kPa

Excess molar volumes of binary mixtures of (fluorobenzene + ethanol), (fluorobenzene + diisopropyl ether), (α,α,α-trifluorotoluene + ethanol), (diisopropyl ether + ethanol), (α,α,α-trifluorotoluene + diisopropyl ether), and the ternary mixtures of (fluorobenzene + diisopropyl ether + ethanol), and (α,α,α-trifluorotoluene + diisopropyl ether + ethanol) were evaluated from density data. The densities were measured with a vibrating-tube densimeter at the temperature 298.15 K and the pressure 101 kPa.The values of the mixing volumes of the ternary systems were predicted in terms of empirical equations using binary solution data alone. The extent of chemical associations among the molecules forming the mixtures is discussed.     

Fluorobenzene-argon ground-state intermolecular potential energy surface

The ground-state intermolecular potential energy surface for the fluorobenzene-argon van der Waals complex is evaluated using the coupled-cluster singles and doubles including connected triple excitations model, with the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. In the surface minima the Ar atom is located above and below the fluorobenzene plane at a distance of 3.562 A from the fluorobenzene center of mass and at an angle of 6.33 degrees with respect to the axis perpendicular to the fluorobenzene plane. The corresponding binding energy is 391.1 cm(-1). Both these results and the eigenvalues obtained from the potential compare well with the experimental data available.     

Temperature Effect on Liquid-Liquid Phase Equilibria of Aqueous Solutions of Fluorobenzene in Ethanol at the Pressure 101.2 kPa

Solubilities and liquid-liquid equilibrium (LLE) data for (water + ethanol + fluorobenzene) solutions are determined at T = (288.15, 298.15, 308.15) K and atmospheric pressure. The titration method is used to construct the binodal curves. All measured solubilities and liquid-liquid equilibrium data are reproduced quantitatively by empirical equations and the NRTL activity coefficient model. The correlated data are consistent to better than 0.3% in phase composition. The studied temperatures have a small effect on the phase equilibrium properties of the investigated systems. The influence of water concentration on the distribution coefficient of ethanol in the coexistent liquid phases and on the fluorobenzene selectivity is important. Practically, fluorobenzene may well be used to produce absolute alcohol.     

Electronic structure of monosubstituted benzenes and X-ray emission spectroscopy

The electronic structure of fluorobenzene was investigated by X-ray emission spectroscopy (using the F−Kα- and C−Kα-spectra) and quantum-chemical MNDO calculations. Molecular orbitals of fluorobenzene were compared with those of benzene and hydrogen fluoride. The P_π−p_π-interaction between the phenyl ring and the fluorine atom in the fluorobenzene molecule is weak for both the outer and inner π levels. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1454–1460, August, 1997.     

The fluorobenzene-argon S(1) excited-state intermolecular potential energy surface

We evaluate the first excited-state (S1) intermolecular potential energy surface for the fluorobenzene-Ar van der Waals complex using the coupled cluster method and the augmented correlation-consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. To calculate the S(1) interaction energies, we use ground-state interaction energies evaluated with the same basis set and the coupled cluster singles and doubles (CCSD) including connected triple excitations [CCSD(T)] model and interaction and excitation energies evaluated at the CCSD level. The surface minima are characterized by the Ar atom located above and below the fluorobenzene ring at a distance of 3.5060 A with respect to the fluorobenzene center of mass and at an angle of 5.89 degrees with respect to the axis perpendicular to the fluorobenzene plane. The corresponding interaction energy is -425.226 cm(-1). The surface is used in the evaluation of the intermolecular level structure of the complex, and the results are compared to the experimental data available and to those found in previous theoretical papers on ground-state potentials for similar complexes.     

A 13C?{1H} double resonance study of the signs of 1H?19F and 13C?19F spin coupling constants in fluorobenzenes and 2-fluoropyridine

The signs of all ¹³C? ¹⁹F and ¹H–¹⁹F coupling constants in fluorobenzene, some substituted derivatives, and in 2-fluoropyridine have been related using single-frequency ¹³C? {¹H} double resonance techniques. All ¹³C? ¹⁹F couplings in these compounds are shown to be positive. Direct experimental proof is given for a positive sign for the small five-bond ¹H? ¹⁹F coupling constant (=0.2—0.3 Hz) in fluorobenzene. The positive sign for ⁴J(C-4, F) in fluorobenzene is in accord with a positive π-electron contribution to this coupling.     

Perfluoropolymer-supported fits reagents

Perfluoropolymer-supported FITS reagents (FITS-Nafion) were synthesized by treatment of bis(trifluoroacetoxy)iodoperfluoroalkanes with perfluorosulfonic acid resin (Nafion-H) and benzene or fluorobenzene.     

Pyrene fluorescence measurements of metastable oil droplets in surfactant-free oil-in-water emulsions

 The fluorescence behavior of pyrene in oil droplets of a surfactant-free oil-in-water emulsion was studied for benzene, fluorobenzene, n-hexane and cyclohexane droplets in water. The excimer–monomer fluorescence ratio immediately after sonication, I _E/I _M(0), of the benzene/water emulsion was 8–10 times larger than for the benzene solution. The ratio I _E/I _M(t) increased in the first 10–20 min before it decreased to zero. Similar behavior was observed for the fluorobenzene/water emulsion, while I _E/I _M(0) for emulsions with n-hexane and cyclohexane was smaller than for benzene and fluorobenzene/water emulsions. I _E/I _M(t) hardly changed with time for the n-hexane and cyclohexane/water emulsions. This different behavior was attributed to the increased solubility of nanometer-size droplets with benzene and fluorobenzene. Received: 20 June 2001 Accepted: 19 April 2001     

Ultrafast dynamics in the dispersed phase of oil-in-water microemulsions: monosubstituted benzenes incorporated into dodecyltrimethylammonium bromide (DTAB) aqueous micelles

Time-resolved optical Kerr effect spectroscopy has been used to probe the molecular environment afforded by the hydrophobic core of oil-in-water microemulsions. This was achieved by measuring the ultrafast dynamics of a series of benzene derivatives (benzonitrile, nitrobenzene, fluorobenzene, styrene, and toluene) incorporated as the oil phase within oil-in-water microemulsions and comparing them to the dynamics in neat liquid and the liquid diluted in nonpolar solvent. Polar and strongly interacting liquids (benzonitrile and nitrobenzene) showed dynamics in the microemulsion that are similar to those in the solution phase, while weakly interacting and mildly polar liquids (fluorobenzene, styrene and toluene) reveal dynamics more similar to those of the neat liquid. This suggests stabilization of the polar dispersed phase in polar regions of the micelle.     

The effect of including polarization functions on the geometrical parameters calculated for benzene,fluorobenzene and cyanobenzene

The geometrical parameters for benzene, fluorobenzene, and cyanobenzene have been calculated using the 6–31G*(5D) and 6–31G** basis sets, and, in addition, the 6–31 + G*(5D) basis set in the case of fluorobenzene. Compared to previous results obtained using the 6-31G basis set there are minor changes in the magnitude of the bond lengths and angles in the ring, but the relative values remain unaltered. The values for the ipso angles in fluorobenzene and cyanobenzene are again somewhat less than those reported from microwave and/or electron diffraction studies. The distortion of the ring is characterized as either an elongation or a flattening with respect to the F–C₁ ⃛C₄ and NC C₁C₄ axes, and the shape is characterized as either a broadening or a narrowing across the ring just below the F and Cn group, i.e., an increase or a decrease in the C₂ ⃛C₆ internuclear distance, relative of the C₃ ⃛C₅ distance.     

[F]Fluorophenyl organometallics as intermediates of no-carrier-added F-fluoroarylation reactions

Based on the recent availability of no-carrier-added (n.c.a.) 1-bromo-4-[¹⁸F]fluorobenzene with high radiochemical yield, the 4-[¹⁸F]fluorophenyl compounds of lithium, sodium and magnesium can now also effectively be prepared. Thus, [¹⁸F]fluoroarene reagents with a nucleophilic reaction centre are available and suitable among others for the formation of [¹⁸F]fluorophenyl compounds with electron donating substituents in the radiosynthesis of ¹⁸F-labelled complex organic structures. For these arylation reactions, however, the presence of macroscopic amounts of a haloarene as co-reactant is necessary with all n.c.a. [¹⁸F]fluorophenyl metallics. The ¹⁸F-fluoroarylation was verified for examples of aryl-carbon, -silicon, -sulphur, and -nitrogen bond formation with radiochemical yields of 20-25% related to the starting radioactivity of [¹⁸F]fluoride.     

Halogenated arenes in the Duff reaction at high pressures

The reaction of fluorobenzene with urotropine in trifluoroacetic acid (TFAA) at high pressures and temperatures affords predominantly fluorobenzaldehydes andN-(fluorophenylmethyl)trifluoroacetamides. The yields of these products depend considerably on the reaction conditions. The rates of their formation have the maximum values at the momemt of the phase transition (PT) of TFAA. A new efficient cyclic (dynamic) regime is proposed for the synthesis at high pressures. The regime involves periodically occurring PT of the solvent. The change in the relative rate of product formation with the degree of fluorobenzene conversion is wave-like.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 319–323, February, 1995.     

Suzuki cross-coupling reaction of fluorobenzene with heterogeneous palladium catalysts

In this work, we accomplished for the first time the Suzuki cross-coupling reaction between fluorobenzene and phenylboronic acid with different heterogeneous catalysts and bases. The conversion values obtained are similar to those provided by homogeneous catalysts and activated aryl fluorides.