N-heptane Solution Research Articles

Electron transfer singlet quenching and exciplexes in the photoreaction of substituted anthracenes with indole derivatives

The effect of substituents on the singlet quenching and photoreaction of anthracene with indole derivatives was investigated in acetonitrile and n-heptane solutions at 298 K. The photoreaction proceeds by the quenching of the excited singlet of anthracene by the indoles. Bimolecular quenching rate constants in acetonitrile follow a Rehm-Weller type correlation. In the nonpolar solvent n-heptane. the rate constants are of the same order of magnitude than those in acetonitrile. However, methyl substitution at the N heteroatom of the indole greatly reduces the quenching in this solvent. In these cases, exciplex emission was observed. These differences in quenching capacity may be explained by a charge transfer interaction followed by proton transfer in the excited state, when it is available at the N-H bond. A nonreactive decay route and exciplex emission is operating in the case of the N-CH 3 derivatives. Photobleaching quantum yields were also determined in heptane. The substitution by methyl or cyano groups at 9 and 10 positions on the anthracene ring decreases the reaction quantum efficiency.

Quenching of diphenylmethane triplet by energy transfer to diphenylmethyl radical in solution

Energy transfer from the diphenylmethane triplet to the diphenylmethyl radical in n-heptane solution has been studied by nanosecond fluorescence and absorption spectroscopy. Both the triplet and the radical are produced by excitation of diphenylmethane with a 266 nm pulse, and the sensitized fluorescence of the radical is observed. A unimolecular rate of (2.9±0.1)×105 s-1 for decay of the triplet and a bimolecular rate of (1.8±0.5)×1010 d mol-1 s-1 for quenching of the triplet by the radical are obtained.

Excess, Partial, and Molar Volumes of n-Alkanes in Near-Critical and Supercritical Water

Densities of solutions of n-pentane, n-hexane, n-heptane, and n-octane in near-critical and supercritical water were measured at pressures between 4 and 38 MPa and temperatures from 643.15 to 648.15 K over the entire composition range. The measurements were performed at three isotherms: 643.15, 647.05, and 648.15 K. A constant-volume piezometer was used to measure the PVTx data. The overall accuracy of the pressure, density, temperature, and mole fraction data are ±0.15%. ±0.5%, ±10mK and ±0.0002, respectively. From these results, excess and partial molar volumes were determined. The uncertainties of the derived results are given. Analysis of the results for dilute water + n-alkane mixtures showed that partial molar volume of n-alkane (solute) and excess molar volume of the mixture near the critical point of pure water (solvent) exhibit remarkable anomalies. The experimental values of molar volumes are compared with predicted values based upon scaling theory. Analysis of the results confirms the prediction of scaling theory that along the critical temperature and pressure of water the limiting partial molar volume of alkane as mole fraction x → 0 is proportional to x−γ/βδ, where γ/βδ ≍ 0.79. Our results contribute to understanding of supercritical solubility in near-critical fluids.

Photodissociation of C–H and C–O bonds of p-methoxytoluene and p-methoxybenzyl alcohol in solution

The photodissociation of p-methoxytoluene and p-methoxybenzyl alcohol at 266 nm in n-heptane solution is studied by nanosecond fluorescence and absorption spectroscopy. The formation of a p-methoxybenzyl radical is identified by its fluorescence which is induced by excitation at 308 nm. The yields of the radical are of the order of ∼10−3 for dissociation of p-methoxytoluene and p-methoxybenzyl alcohol. The growth rate of 1.5×108 s−1 for the radical is equal to the decay rate of (1.5±0.3)×108 s−1 for the precursor fluorescence in dissociation of p-methoxytoluene, whereas the growth rate of >1.0×109 s−1 for the radical is much faster than the decay rate of (1.8±0.3)×108 s−1 for the precursor fluorescence in dissociation of p-methoxybenzyl alcohol. The formation of the radical depends linearly on the photolysis pulse fluence for dissociation of p-methoxytoluene and p-methoxybenzyl alcohol. The data show existence of two distinct dissociation channels. p-Methoxytoluene dissociates from thermally equilibrated levels of the S1 state after vibrational relaxation, whereas p-methoxybenzyl alcohol dissociates from vibrationally excited levels of the S1 state in competition with vibrational relaxation. The difference of these channels is explained on a model of electronic coupling between the precursor and product states in the geometry where the C–H and C–O bonds are stretched in a plane perpendicular to the benzene rings. For p-methoxytoluene, the S1 state does not correlate adiabatically to the ground state of the C–H bond fission products, so intersystem crossing or internal conversion precedes dissociation. For p-methoxybenzyl alcohol, avoided crossing between the ππ* (benzene) configuration and the np(O)σ*(C–O) repulsive configuration results in the adiabatic potential-energy surface which evolves to the ground state of the C–O bond fission products allowing rapid dissociation.

Emulsion precipitation of submicron zinc oxide powder

Ultrafine zinc oxide powder was successfully synthesized through the emulsion precipitation process. The aqueous solution containing zinc cations was well emulsified in n-heptane solution, and then precipitated by adding ammonia. After calcination of the precipitates, submicron zinc oxide powder with a near spherical morphology was obtained. On comparison with the conventional precipitation method, this developed process was confirmed to be superior in preparing uniform ZnO powder and reducing its particle size. The emulsion stability was significantly affected by the ratio of the volume of the oil phase to that of the aqueous phase, and this ratio also influenced the mean particle size of ZnO powder.

Remarkable Stability of (η5-C5H5)Re(CO)2L (L = n-Heptane, Xe, and Kr): A Time-Resolved Infrared Spectroscopic Study of (η5-C5H5)Re(CO)3 in Conventional and Supercritical Fluid Solution

Employing fast time-resolved infrared (TRIR) spectroscopy we have characterized CpRe(CO)2(n-heptane), CpRe(CO)2(Xe), and CpRe(CO)2(Kr) (Cp = η5-C5H5) at or above room temperature in n-heptane, supercritical Xe, and Kr solution. The reactivity of CpRe(CO)2(n-heptane) with CO (k2 = 2.1 (±0.5) × 103 mol-1 dm3 s-1) shows this complex to be the least reactive of the reported organometallic alkane complexes. We report a trend in reactivity of the early transition metal alkane complexes. CpRe(CO)2(Xe) and CpRe(CO)2(Kr) are also shown to have significant stability. CpRe(CO)2(Xe) is less reactive toward CO than all of the reported alkane complexes except CpRe(CO)2(n-heptane).

Kinetics and mechanism of oligosiloxanol condensation and oligosiloxane rearrangement catalysed with model phosphonitrile chloride catalysts

The condensation kinetics of 1,1,3,3,3-pentamethyldisiloxanol (MDH) in n-heptane solution were compared for two types of phosphonitrilic catalyst, hexachloro-1 λ-diphosphaza-l-enium hexachloroantimonate salt, [Cl 3PNPCl 3] +[SbCl 6] −, 1, and P-trichloro- N-dichlorophosphoryle phosphazene, [Cl 3PNP(O)Cl 2], 2. The kinetic law of reaction is not changed when 1 is replaced by 2. The process is selective leading to linear decamethyltetrasiloxane (MD 2M, where D denotes the dimethylsiloxane unit, and M denotes the trimethylsiloxane unit) as almost the exclusive primary product. Other oligomers of the MD n M series are formed as a result of the MD 2M rearrangement. The MD 2M rearrangement was studied in separate experiments in the absence of the siloxanol and water. Both catalysts 1 and 2 gave similar rate—concentration behaviour. Some of the kinetic features of the process resemble those of chain reactions and mechanisms of the MDH condensation, and the MD 2M rearrangement are discussed.

Extraction Equilibria of Amino Acids by Di(2-ethyl hexyl) Phosphoric Acid in n-Heptane Solutions.

Extraction Equilibria of Amino Acids by Di(2-ethyl hexyl) Phosphoric Acid in n-Heptane Solutions.

Self-association of 1,2-diols Apparent heat capacities of 1,2-diols in n-heptaneand carbon tetrachloride

Apparent molar heat capacities at constant pressure, Cmapp, have been measured for several 1,2-diols in dilute n-heptane and carbon tetrachloride solutions at 25 °C. The systems were: hexane-1,2-diol, octane-1,2-diol and decane-1,2-diol in n-heptane and butane-1,2-diol, pentane-1,2-diol, hexane-1,2-diol, octane-1,2-diol, decane-1,2-diol and dodecane-1,2-diol in carbon tetrachloride; in addition, values of Cmapp for hexan-1-ol and decan-1-ol in carbon tetrachloride were determined. The experimental values of Cmapp show a maximum against diol concentration which is larger and shifted to smaller concentrations than that for the equal carbon number 1-alcohol, indicating that the self-association capability of the 1,2-diols is greater than that of the monoalcohols. The contribution to Cmapp arising from intramolecular H-bonding is small compared to that arising from the intermolecular H-bonds. Diol and monoalcohol self-association is reduced in going from the inert n-heptane to CCl4, which acts as a weak proton acceptor. The data for 1,2-diols when plotted against ψ1, the concentration of hydroxy groups in the mixture, follow a single, corresponding states curve for each of the solvents. To interpret these heat capacity data, an extension of the Treszczanowicz–Kehiaian (TK) model for associated liquids has been undertaken. This extension takes into account the formation of intramolecular H-bonds. The parameters of the model, i.e. equilibrium constants and enthalpies of association, have been fitted to the data. It is concluded that at the dilute 1,2-diol concentrations used here, the heat capacity data can be well explained considering that there is only one predominant species in the solution, viz. pentamers or hexamers.

Rydberg structures in the gas-phase electronic absorption spectra of η-cycloheptatrienyl η-cyclopentadienyl complexes of molybdenum

S. Yu. Ketkov and J. C. Green, J. Chem. Soc., Faraday Trans., 1997, 93, 2467 DOI: 10.1039/A700372B

Spectroscopy in the Ultraviolet and Visible Regions As Studied by Solution-Phase and Vapor-Phase Photoabsorption in the Ultraviolet and Visible Regions

The electronic absorption spectra of (η7-C7Η7)(η5-C5Η5)V and (η7-C7Η7)(η5-C5H4Me)Ta in n-heptane solution and in the vapor phase have been measured. Assignments of absorption features in the soluti...

Luminescence behaviour of 7-hydroxyflavone in aerosol OT reverse micelles: excited-state proton transfer and red-edge excitation effects

The fluorescence emission properties of 7-hydroxyflavone (7HF) are examined in reverse micelles of aerosol-OT (AOT) in n-heptane. Excited-state proton transfer (ESPT) leading to dual-emission behaviour ( λ max ≈ 396–417 nm and 545–550 nm which can be assigned to the normal and ESPT tautomer emission respectively) as well as red edge excitation shift (REES) of the normal fluorescence band are observed. Upon gradual addition of water to the 7HF-AOT- n-heptane solution, conspicuous enhancement of the ESPT tautomer emission intensity takes place together with a progressive red shift of the normal emission, that continues up to ([H 2O]/[AOT]) = W 0 ≈ 8–10, beyond which no significant changes occur. Interestingly, with increasing value of W 0, the changes observed in the magnitude of the REES effect, Δλ (Δ λ is the difference in λ max of the normal fluorescence as λ exc is shifted from midband ( λ = 310 nm) to red edge ( λ = 350 nm) of the absorption band) parallel to changes in the λ max of normal emission, as well as that of the relative intensity I T l N of the tautomer vs. normal emission bands. Even at high W 0 (e.g. W 0 = 36), these parameters do not reach the limiting values found in bulk water, indicating that 7HF is predominantly localized near the head groups of AOT, mostly in the bound water phase.

Characterization of a Single Sample by Combining Thermodynamic and Spectroscopic Information in Spectral Analysis

We have previously shown that chemical equilibria can be characterized spectroscopically, even when the component spectral responses are unknown and overlapping, by exploiting appropriate thermodynamic relations (Kubista, M.; Sjoback, R.; Albinsson, B. Anal. Chem. 1993, 65, 994−998). Application of this strategy requires sets of samples that differ in a physical property, such as pH or total concentration. In this work, we show that a similar strategy can be applied to characterize a single sample. Utilizing the van't Hoff relation, which describes the dependence of the equilibrium constant on temperature, we show that spectra recorded at different temperatures can be deconvoluted into contributions from the individual components. To illustrate the approach, we characterize two monomer/dimer equilibria, thiazole orange in aqueous solution and benzoic acid in n-heptane, by studying the effect of temperature on the absorption spectrum. We determine the spectral responses of the monomer and dimer species, th...

Solvation Dynamics of Coumarin 480 in Reverse Micelles. Slow Relaxation of Water Molecules

The picosecond time-resolved Stokes shift of the laser dye coumarin 480 (I) is studied in Aerosol OT-heptane reverse micelles at various concentrations of water. On addition of water to a n-heptane solution of I containing 0.09 M AOT, the emission spectrum of I exhibits a prominent shoulder at 480 nm which is ascribed to the dye molecules in the water pool of the reverse micelles. In n-heptane, the fluorescence decays of I at short and long wavelengths are identical, which rules out any time-resolved Stokes shift. On addition of water to the AOT/heptane system, the decay at long wavelengths exhibit a distinct growth on the nanosecond time scale. This and the time-dependent Stokes shift indicate that the water molecules in the water pool of the AOT reverse micelles undergo slow relaxation on the nanosecond time scale.

Solid-state studies on C 60 solvates grown from n-heptane

Crystallographic and thermodynamic experiments show that crystalline C 60 obtained by slow evaporation of solutions in n-heptane is a C 60, n-heptane 1:1 solvate. Its lattice is hexagonal, Laue class 6/mmm, with a = 10.00(4) Å and c = 10.16(1) Å. No transition is observed at temperatures higher than 100 K, and desolvation into fcc C 60 occurs at about 360 K with ΔH = +43.5 J g −1, close to the sublimation enthalpy for pure n-heptane. Another binary compound, presumably a polymorph of the former, is sometimes obtained by rapid evaporation of toluene + n-heptane mixtures. Its lattice is orthorhombic, Immm, with a = 10.07 Å, b = 10.22 Å and c = 48.9 Å.

Photoacoustic Calorimetry at High Pressure: A New Approach to Determination of Bond Strengths. Estimation of the M-L Bond Dissociation Energy of M(CO)5L (M = Cr, Mo; L = H2, N2) in n-Heptane Solution

Photoacoustic Calorimetry at High Pressure: A New Approach to Determination of Bond Strengths. Estimation of the M-L Bond Dissociation Energy of M(CO)5L (M = Cr, Mo; L = H2, N2) in n-Heptane Solution

Photochemistry of [CpMo(CO)3]2. Direct Detection and Kinetics of the Radical CpMo(CO)3 in n-Heptane Solution at Room Temperature by Fast Time-Resolved Infrared Spectroscopy

Photochemistry of [CpMo(CO)3]2. Direct Detection and Kinetics of the Radical CpMo(CO)3 in n-Heptane Solution at Room Temperature by Fast Time-Resolved Infrared Spectroscopy

Luminescence behavior of 7-azaindole in AOT reverse micelles

The fluorescence emission properties of 7-azaindole (7AI) are examined in aerosol-OT (AOT) reverse micelles in n-heptane. The emission dramatically changes from a typical dual fluorescence (λ max≈326, 480 nm) behavior in n-heptane, to a single fluorescence band (λ max≈ 350 nm) with enhanced yield in the presence of AOT. Upon progressive addition of water to the 7AI/AOT/ n-heptane solutions the emission undergoes a red-shift, along with significant decreases in quantum yield and drastic changes in decay kinetics. The results are interpreted in terms of the variations in the microenvironments of 7AI, which depend in a sensitive manner on the water/surfactant molar ratio.

Adsorption of benzoic acid from organic solvents on calcite and dolomite: Influence of water

A study has been carried out of the adsorption of benzoic acid from cyclohexane solution onto the hydrophilic surface of calcite. We determined initially the chemical and mineral composition of the solid, its specific surface area and its granulometry. This was followed by the determination of the enthalpies of immersion of calcite in different solvents. These thermodynamic properties gave information on the energetics of calcite—solvent interactions. In this way, we could construct a scale of affinities of the different organic molecules and water for the calcite surface. It was noted that the enthalpies were higher in unsaturated than in saturated organic solvents, and higher in water than in the organic solvents. The adsorption isotherms and the differential molar enthalpies of displacement were determined in the presence and the absence of water. The role played by water in the adsorption of polar organic molecules from the oil phase has not been clearly explained previously. In this paper, we indicate how the presence of water can modify the adsorption of aromatic compounds on the surface of calcite. As regards the adsorption isotherms, the presence of water essentially increases the amount of adsorption. The results of the calorimetric studies were found to be surprising; we observed that the differential molar enthalpies of displacement were endothermic. Similar experiments were carried out with dolomite and n-heptane solution and the results compared with those obtained with calcite and cyclohexane, leading to the formulation of a general model concerning the adsorption of small polar organic molecules from organic solvents onto the surfaces of the carbonates.

Extraction of technetium(VII) from uranium(VI) in nitric acid system by primary amine — n-heptane solution

Separation of technetium(VII) from uranium(VI) has been studied through experiments on the coprecipitation of technetium(VII) with precipitation of ammonium diuranate, and on the extraction of technetium(VII) from a 3M aqueous nitric acid solution using, as extractant, a primary amine (Primene JMT) dissolved in either chloroform or n-heptane solution. Ammonium diuranate precipitation proved to provide the most satisfactory means of separating technetium(VII) from uranium(VI) in solution. Extraction of technetium(VII) contained in nitric acid solution using Primene JMT dissolved in n-heptane solution proved to be quantitative after several cycles of the procedure and alternatively, upon raising to 5∶1 the volume ratio between the organic phase containing the extractant and the aqueous phase containing technetium(VII). Stripping of technetium(VII) into 2M aqueous ammonium carbonate solution was enhanced to quantitative level by repetition of the stripping procedure, and alternatively, by adding the ammonium carbonate in a volume ratio of 5∶1 with respect to the organic phase containing technetium(VII).