Development of a Henry’s constant correlation and solubility measurements of n-pentane,i-pentane,cyclopentane, n-hexane,and toluene in water

In this communication, we report new experimental data on n-pentane, i-pentane, cyclopentane, n-hexane, and toluene solubility in water at low temperature (below 298.15 K) and atmospheric pressure conditions. The new experimental data together with those reported in the literature have been used in developing a new equation for Henry’s constants of normal alkanes (methane to decane), BETEX compounds, and acid gases in aqueous phase over a wide range of temperature (typically from 273.15 K to 373.15 K). The new equation is based on a thermodynamic model, which uses the Peng–Robinson equation of state combined with the classical quadratic mixing rules for modelling non-aqueous phases, while the NRTL model is used to calculate the water activity.The predictions of the developed thermodynamic model are compared to the experimental data and the results of a thermodynamic approach, which uses the Valderrama modification of the Patel–Teja equation of state and non-density dependent mixing rules for modelling all fluid phases. Good agreement is observed between the experimental data and the model predictions.     

Henry’s law constant for environmentally significant compounds

Many nonvolatile organic compounds, e.g., polyaromatic hydrocarbons (PAHs), are readily stripped during aerobic biodegradation. This is because of the high infinite dilution activity coefficient resulting from forces generated by the water-organic interactions at the molecular level. Several models have been proposed for air-stripping based on the Henry’s law constant. By definition, the Henry’s law constant is the infinite dilution activity coefficient multiplied by the pure component vapor pressure. In this article, a gas saturation technique was used to measure the very low vapor pressures exhibited by these nonvolatile compounds. Literature values of other PAHs have been tabulated and are presented. For determining infinite dilution activity coefficients, a differential ebulliometery apparatus has been constructed. In this technique, the boiling point difference between pure water and a water-organic solution is measured very precisely. Thermodynamics is then used to calculate the infinite dilution activity coefficient. The method’s accuracy has been tested using the phenol-water system.     

Is the Hammett's constant free of steric effects?

In this work, we have explored the validity of the hypotheses on which rest the Hammett's approach to quantify the substituent effect on a reaction center, by applying two DFT energy decomposition schemes. This is performed by studying the change in the total electronic energy, ΔΔE, associated with a proton transfer isodesmic equilibrium. For this reaction, two sets of substituted benzoic acids and their corresponding benzoate anions have been considered. One of these sets contains para- and meta-substitutions, whereas the other one includes ortho-substituted benzoic acids. For each case, the gas phase change in the total electronic energy has been calculated, and two DFT energy decomposition schemes have been applied. The experimental σ(X) was found to be nearly proportional to the computed ΔΔE. The results for the para- and meta-substituted benzoic acids lead to the conclusion that it is possible to treat separately and, in an additive manner, the electrostatic and steric contributions; and also that the Hammett constant depends mainly on the electronic contributions to the free energy, while the steric contribution is negligible. However, the results for the ortho-substituted cases lead to the conclusion, as was assumed by Hammett, that there are significant qualitative differences between the effects on a reaction site of substituents in the meta- and para-positions and those in the ortho-position.     

Determination of Henry’s constant using a photoacoustic sensor

We present a simple method for measuring Henry’s constant k_Hof ethanol using photoacoustic spectroscopy. At T =  298.1 K the measured value fork_H is (0.877  ±  0.039)kPa · kg · mol ^− 1. Our data show that Henry’s law is valid at ethanol molalities between 0.1mol · kg ^− 1 and 1.4 mol · kg ^− 1. The temperature dependence of Henry’s constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T =  273.1 K and T =  298.1 K. By analysing the gas phase concentration and applying Henry’s law, an ethanol molality of 0.864 mol · kg ^− 1in the liquid phase can be measured with an error of  ± 0.038mol · kg ^− 1. The detection limit of the photoacoustic sensor is a gaseous ethanol pressure of 10 ^− 3kPa. Ethanol molality changes as low as 1.10 ^− 3mol · kg ^− 1can be measured.     

Coordination model,stability constant,and kinetics study of cystamine and l-cystine with [PdCl4]2− in hydrochloric aqueous solutions

Stoichiometry, equilibria, and kinetics of [PdCl₄]^2?interactions with l-cystine (H₄CysS²⁺) and cystamine (H₂Cyst²⁺) have been investigated spectrophotometrically in strong hydrochloric acidic media. Interactions lead to the formation of highly stable S/(S,N)-coordinated binuclear, and then with excess [PdCl₄]^2? trinuclear (S,S,N) or tetranuclear (S,S,N,N) species without disulfide bond cleavage. The reaction of [PdCl₄]^2? with H₄CysS²⁺ or H₂Cyst²⁺ at [PdCl₄]^2? excess has irreversible first-order kinetics, and with H₄CysS²⁺ or H₂Cyst²⁺ excess, by irreversible parallel reaction of [PdCl₄]^2? addition to the ligand. The influence of leaving groups on the kinetics has been explained in terms of formation of stable ionic pairs with complex species and of efficient overlap of d and π orbitals in a transition state. The reactions proceed through an associative mechanism with the first step being formation of the S-coordinated complex. Coordination models and mechanisms have been proposed. Applicability of spectrophotometry for establishment of disulfide bond state in organic disulfides in complexation processes has been demonstrated.     

Standard potential of the Ag-AgCl electrode and acidity constant of glycine at constant molality of NaCl in glucose-water mixed solvents from 278.15 to 318.15 K

Standard electrode potentials E° of Ag-AgC1 electrode in molality scale and acidityconstants of glyeine pK_1° at constant molality of NaCl (1.0 mol·kg~(-1)) in 5 and 15 mass%glucose-water mixed solvents over a range of temperatures from 278.15 to 318.15 K weredetermined from precise emf measurements.The dependence of acidity constant on temperatureis given as a function of the thermodynamic temperature T by an empirical equation, pK_1°=A_1(K/T)-A_2+A_3(T/K).The corresponding thermodynamic quantities of the first dissociationprocess of glycine were calculated and the effects of both tho solvent and the salt on themwere also discussed.     

Studies on dynamic dissociation constant of 99Mo–insulin complex

In this article we studied the dynamic dissociation constant (k _d) of ⁹⁹Mo complexed with insulin molecule at various pH. The k _d values were determined by dialysis technique against deionised water. The T _1/2 of the molybdenum–insulin complexes were found to be 6.41, 5.25 and 3.5 h at pH 5, 6 and 7 respectively. The half-lives indicate that insulin may act as good carrier of ⁹⁹Mo to the intestine and may be useful in the field of nuclear medicine.     

Protonation constants of α-alanine in electrolyte mixtures at constant ionic strength

The stoichiometric acid-base equilibrium constants for -alanine in tetraethylamonium iodide-potassium nitrate solutions were determined at a constant ionic strength of 1.4 m at 25°C. The results obtained are discussed on the basis of the Friedman and the Pitzer model for electrolyte mixtures.     

The determination of a π-sigma constant for substituents attached to silicon

The proton, ¹³C, and ²⁹Si chemical shifts and the ¹³C¹H coupling constants of a series of compounds of the type (CH₃)₃SiX were measured and correlated with inductive and resonance σ constants. In order to provide a comparison with a homologous series in which π-bonding is absent, shifts and coupling constants were obtained for the t-butyl series, (CH₃)₃CX. Only the coupling constants gave significant correlations with σ_I. A series of σ constants, presumably reflective of the amount of π-bonding, were obtained from the deviations from the J vs. σ_I plot. The magnitudes of these values indicate that oxygen is a better π-donor than nitrogen and chlorine.     

Vibrational relaxation of NCO(X̃) by rare gases,and rate constant measurement of the NCO + NO reaction

Vibrational relaxation of the v₂ mode of NCO(X̃) by rare gases takes place at rates which are in the order Ne < He ≈ Ar < Kr. The bimolecular rate constant for the NCO + NO reaction is (3.4±0.3)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 295 K.     

Electrical conductivity and dielectric constant measurements of liquid crystal–gold nanoparticle composites

The behaviour of the anisotropic electrical conductivity of liquid crystal–gold nanoparticle (LC‐GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol‐capped GNPs has been investigated. The nematic–isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ_∥) and orthogonal (σ_⊥) to the director shows a much smaller but definite decrease as X increases.     

Henry’s constant of carbon dioxide-aqueous deep eutectic solvent (choline chloride/ethylene glycol,choline chloride/glycerol,choline chloride/malonic acid) systems

In this study, we present a new set of Henry’s constant data for the system carbon dioxide-aqueous deep eutectic solvent (DES) (20 to 80 wt% DES) at T = (303.15, 308.15, and 313.15) K. The DESs used were choline chloride-based: ethaline (choline chloride/ethylene glycol), glyceline (choline chloride/glycerol), and maline (choline chloride/malonic acid). A differential Henry’s coefficient model was used to describe the behaviour of Henry’s constant, and correlate it with temperature and concentration of DES in the aqueous DES solution. The correlation was found satisfactory such that the proposed model can be used in engineering calculations with reasonable accuracy.     

Dosages coulométriques à courant constant et en solution non agitée

Accurate evalution of “transition times” occurring during constant current electrolysis in non-stirred media may be used analytically. An apparatus has been devised for such a purpose.The method has been applied to various practical problems and stress is laid on its potentialities and main features.Under favourable conditions, determinations are performed in less than one minute, with an accuracy of about 0.2%.     

Angular dependence of the β-proton hyperfine coupling constant in β-substituted ethyl radicals

The β-proton hyperfine coupling constants in β-substituted ethyl radicals Ḣ₂-CH₂-X (X = CH₃, NH₂, OH, F, SiH₃, PH₂, SH, Cl) were computed as a function of the rotational angle α about the C_αC_β bond by ab initio calculations at the UHF/DZ + d level. They follow the relation a_H⨿(θ,α) = A + Bcos²θ + C cosθcosα, where A and B are not significantly affected by the substituent, and C is closely related to the electronegativity of the heteroatom.     

Is the rate constant of chain propagation kp in radical polymerization really chain-length independent?

A careful investigation of the k_p data obtained from pulsed-laser polymerization at different pulse separations t₀ in a lot of systems has revealed that k_p exhibits a slight but significant decrease when t₀ is increased, corresponding to an about 20% decrease of k_p extending over several hundreds in degree of polymerization. Transformation of this integral effect to individual chain-lengths reduces this range, of course, but still shows more than one hundred propagation steps to be concerned. This is interpreted in terms of a decrease of the monomer concentration at the site of propagation caused by the segments already added to the growing chain.     

Determination of the emanation coefficient and the Henry’s law constant for the groundwater radon

The radon emanation coefficient (ε) from aquifer rock and the Henry’s law constant (H) of radon were determined by measuring activity concentrations using liquid scintillation counter (LSC). For the evaluation of the method, the coefficients were measured at 0, 10 and 20 °C and the temperature dependency of the coefficients was compared with others. The radon emanation coefficients from the rock particles used in this work are 0.0845, 0.1007 and 0.1308 at 0, 10 and 20 °C, respectively. The dimensionless Henry’s law constants for the groundwater used in this work are 0.994, 1.153 and 2.641 at 0, 10 and 20 °C, respectively. The results show a good agreement with those in literatures.     

An estimation of force constant change of Mössbauer119Sn impurity nuclei in lead host

The recoilless fractionf and the SOD data of Sn as impurity in Pb are analyzed for any force constant change in the framework of MANNHEIM's model. On the basis off-values, the force constant ratio _ih / _hh turns out to be 0.81±0.02. Expectedly no localized modes are found to exist in the system.     

Determination of the stability constant of cobalt-substituted mono-lacunary Keggin-type polyoxometalate and its electrocatalytic water oxidation performance

The anion form of a cobalt-substituted mono-lacunary Keggin-type polyoxometalate (POM) complex in aqueous solution was identified as [Co(H₂O)(H₃PW₁₁O₃₉)]^2? and its stability constant was determined to be 5.19 × 10⁴ by spectrophotometry. Additionally, the electrocatalytic performances toward water oxidation of different concentrations of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? were investigated in the neutral phosphate buffer solution, and it was found that [Co(H₂O)(H₃PW₁₁O₃₉)]^2? anion itself has little activity; the activity of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? solution actually results from dissociated [Co(H₂O)₆]²⁺. This work provides a simple way to understand the origin of catalytic water oxidation activity of a POM-based complex.