Gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous solutions of Fe(II)–CDTA chelate complex

Utilization of ferric chelate complex of trans-1,2-cyclohexanediaminetetraacetic acid (CDTA) for the oxidative scrubbing of H₂S and CH₃SH in Kraft mill streams can be beneficial from the standpoints of iron protection against precipitation and oxygen-mediated regenerative oxidation of the ferrous chelate CDTA. The physical solubility of methyl mercaptan in CDTA–Fe(III) complex cannot be measured directly because of oxidation of the sulfur-bearing gaseous species with the ferric chelate. Therefore, this investigation was carried out to determine the gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous iron-free CDTA solutions and non-reacting ferrous chelate solutions (CDTA–Fe(II) complex), using the static headspace method with an estimated accuracy of about 2%. Experiments with aqueous solutions of chelate concentrations varying between 38 and 300 mol m⁻³ were carried out at temperatures between 298 and 333 K and atmospheric pressure. It was shown that the methyl mercaptan solubility decreases with increasing temperature for all systems but was not much influenced, in the studied conditions, by the chelate concentration especially at larger temperatures.     

Prediction of Henry's law constant of benzene derivatives using quantum chemical continuum‐solvation models

Semiempirical (SM2, SM5.4A, MST‐AM1, COSMO‐AM1) and ab inito (HF/PCM‐vdW, MP2//PCM‐vdW, COSMO‐DFT) dielectric continuum‐solvation models as well as the surface‐tension model SM5.0R are analyzed with respect to predicting Henry's law constant at 25°C using a compound set of benzene and 39 benzene derivatives. Both hydrophilic and hydrophobic compounds are covered with a total variation in Henry's law constant of almost eight orders of magnitude corresponding to 44 kJ/mol, and the data set is selected such that there are cases where subtle changes in the molecular structure result in substantial changes of the free energy of solvation. The calculations with SM2, COSMO‐AM1, and COSMO‐DFT include solution‐phase geometry optimization, and the ab initio results refer to polarized basis sets of double‐zeta quality, with two gradient‐corrected functionals (BPW and BLYP) being used for the DFT‐based models. The results show considerable differences in performance between the different continuum‐solvation models, and among the methods yielding solvation free energies the systematic error ranges from −0.9 kJ/mol (SM5.0R) to 12.1 kJ/mol (MP2//PCM‐vdW). In particular, the nonelectrostatic solvation energy contributions of SM2, SM5.4A, MST‐AM1, and PCM‐vdW do not correlate with each other, and with PCM‐vdW omission of the nonelectrostatic component significantly improves the relative trend. The best statistics after scaling through linear regression are achieved with the electrostatic component of MP2//PCM‐vdW (r=0.94) and with COSMO‐DFT (r=0.93). The discussion includes detailed analyses of pecularities associated with certain functional groups, deviations from the expected relationship between dipole moment and solvation energy, and a simple approach to model dispersion interaction and cavitation energy by surface area terms that differentiate between individual atom types. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 17–34, 2000     

Experimental determination of dissociation constant,Henry's constant,heat of reactions,SO2 absorbed and gas bubble–liquid interfacial area for dilute sulphur dioxide absorption into water

The experimental results for dissociation constant, Henry's constant, heat of reactions and gas bubble–liquid interfacial area for absorption of dilute SO₂ (SO₂ partial pressure upto 0.963 kPa) into water in bubble column are presented. The relations between Henry's constant versus temperature and dissociation constant versus temperature have been proposed based on the present experimental investigation. The temperature dependence on gas bubble–liquid interfacial area per unit volume of liquid has examined. Result shows a very small decrease in interfacial area with increase in temperature. The experimental results are used to correlate total SO₂ absorbed at saturation as function of temperature and SO₂ partial pressure. Comparisons between experimental results and literature data have also been made at different temperatures. The reasonable fittings between the data obtained from correlation and literature data shows that the proposed correlation can be successfully used for predicting the absorption equilibria of dilute SO₂ in distilled water at different temperatures.     

Measurement of activity coefficients at infinite dilution for acetonitrile,water, limonene,limonene epoxide and their binary pairs

Activity coefficients at infinite dilution were determined for binary pairs of acetonitrile, water, limonene and limonene epoxide at room temperature using the dilutor technique (inert gas stripping) in a home-made dilutor apparatus. The activity coefficients were predicted with the Aspen Plus software using the Dortmund-modified UNIFAC contribution method. Values predicted by software simulations are in good agreement with experimental data. However, experimental activity coefficients at infinite dilution obtained for limonene + acetonitrile, water + limonene and limonene epoxide + water systems are in disagreement with reported values estimated from LLE or solubility data.     

The Henry's law constants of water in the binary mixtures of benzene,carbon tetrachloride,and cyclohexane at 25°C

The solubilities of water in each of the three binary mixtures benzene-carbon tetrachloride, benzene-cyclohexane, and carbon tetrachloride-cyclohexane were determined as a function of solvent composition at 25°C. It was found that, as with the pure solvents, water in the 0.50 mole fraction binary mixtures of these solvents obeyed Henry's law up to saturation. The experimentally determined solubilities were converted to Henry's law constants of water for the entire range of solvent compositions. These values for the Henry's law constants were compared with theoretically calculated values. The comparisons indicated that water in the benzene-cyclohexane and in the benzene-carbon tetrachloride mixtures was preferentially solvated by benzene. Preferential solvation of water was not indicated for the carbon tetrachloride-cyclohexane mixtures.     

Solubility of gases in liquids. XVI. Henry's law coefficients for nitrogen in water at 5 to 50°C

The solubility of nitrogen in pure liquid water was measured in the pressure range 45 to 115 kPa and in the temperature range 5 to 50°C. These data are used to obtain Henry coefficients H _2,1 (T,P _s,1 ) at the vapor pressure P _s,1 of water. The temperature dependence of H _2,1 (T,P _s,1 ) is accounted for by both a Clarke-Glew (CG) type fitting equation, and a power series in T^–1, as suggested by Benson and Krause (BK). The imprecision of our measurements is characterized by an average deviation of ±0.038% from a four-term CG equation, and by an average deviation of ±0.042% from a three-term BK equation. From the temperature variation of H _2,1 (T,P _s,1 ) partial molar quantities referring to the solution process, such as enthalpies and heat capacities of solution, are obtained. They are given in tabular form, together with H _2,1 (T,P _s,1 ) and derived Ostwald coefficients L, at rounded temperatures. Finally, experimental results are compared with values calculated via scaled particle theory.     

Relation between stability constants of metal ion cryptates in two solvents and the transfer activity coefficients of the metal ions

The extrathermodynamic assumption of Lejaille and Bessière that _1,2 log K (LM ⁿ⁺ )=–G _tr (M ⁿ⁺ ) in which K is stability constant and L is cryptand 2.2.2, 2 _B 2 _B 2, 2.2.1, or 2.1.1 has been tested in dipolar aprotic solvents for M ⁿ⁺ being Li⁺, Na⁺, K⁺, Ag⁺, Tl⁺, and Ba²⁺. The relation has been found generally acceptable for the dipolar aprotic solvents propylene carbonate, acetonitrile, N,N-dimethylformamide and dimethylsulfoxide, provided the size of the ion is equal to or smaller than the cavity of the cryptand. The relation does not hold for the hydrogen bonded donating solvents, water, and methanol.     

Henry's constants of n-alkanols (methanol through n-hexanol) in water at temperatures between 40°C and 90°C

Henry's constants of n-alkanols (methanol to n-hexanol) in water were measured at temperatures between 40°C and 90°C using a recently developed headspace gas chromatographic technique. The data were in good agreement with literature data when available. The consistency of the data was verified by comparing calculated partial molar enthalpies with calorimetric values. The temperature dependence of dimensionless Henry's constants was fitted with the classical van't Hoff equation and an empirical correlation was established for the dimensionless Henry's constants as a function of temperature and number of carbon atoms in the n-alkanol.     

Importance of the Debye interaction in organic solutions: Henry's law constants for polar liquids in nonpolar solvents and vice versa

Henry's law constants have been determined for -butyrolactone (BL), ethyl acetate (EA), and 2-methyl-3-pentanol (MEP) in mixtures of iso-octane (ISO) and toluene (TOL), for BL, EA, TOL, and ISO in cinnamaldehyde (CIN) and for TOL and ISO in each other and in BL. From these data and published vapor pressures, the activity coefficients at infinite dilution and the standard molar Gibbs free energy of transfer, G ₂ ⁰ of the solutes from dilute solution in ISO to dilute solution in each solvent medium have been calculated. The different behavior patterns of BL and EA are attributed to differences in their abilities to exist in different conformations possessing different dipole moments. For polar solutes, G ₂ ⁰ decreases with increasing polarizability of the solvent and with increasing dipole moment of the solute, suggesting increased contributions from dipole-induced dipole (Debye) interactions. The sigmoidal plot of G ₂ ⁰ against the change in pair potential energy calculated from the classical expressions suggests that G ₂ ⁰ seriously underestimates the strength of the Debye interactions in comparison with the London interactions.     

Stabilities in water and transfer activity coefficients from water to nonaqueous solvents of 15-crown-5 and 16-crown-5-metal ion complexes

Stability constants of 1 : 1 16-crown-5 (16C5)-metal ion complexes were determined in water at 25°C by conductometry and potentiometry with ion-selective electrodes. The selectivity sequences of 16C5 in water for univalent and bivalent metal ions are Ag⁺ > Na⁺ Tl⁺ > K⁺ and Sr²⁺ > Ba²⁺ Pb²⁺, respectively. The stability of a given 16C5-metal ion complex in water is much lower than might be expected on the basis of the solvation power (i.e. relative solubility of the metal ion) of water for the metal ion. The same tendency is observed for the cases of 15-crown-5 (15C5) -metal ion complexes. Transfer activity coefficients () of 15C5 and 16C5 for tetradecane (TD)/water, TD/methanol, TD/acetonitrile, and propylene carbonate/water systems were determined at 25°C. From these data, contributions of a methylene group and an ether oxygen atom to the log value of a crown ether were then obtained. The values from water to acetonitrile, propylene carbonate, and methanol of 15C5- and 16C5-univalent metal ion complexes were calculated, s, M⁺, and L being a solvent, a univalent metal ion, and a crown ether, respectively. The log value is greater than the corresponding log value. The log values are negative. This indicates that, although the M^- ions are more soluble in water than in the nonaqueous solvents, when the crown ether forms a complex with the M⁺ ion, the complex becomes more soluble in the nonaqueous solvents than in water, compared with the free crown ether. It was concluded from this finding that the unexpectedly low stability of the crown ether-M⁺ complex in water is attributed to strong hydrogen bonding between ether oxygen atoms of the free crown ether and water.     

Simple methods for the estimation of ionization constants of substituted pyridine N-oxides in polar aprotic solvents and water

A direct method for the determination of the pK _a values of acids conjugated to substituted pyridine N-oxides has been proposed which is based on the pH measurement of the solution of the basic salt. It has been experimentally shown that the method is reliable when applied to N-oxides of not too low basicity (pK _a >5). Correlation has been performed between the pK _a values in aqueous and aprotic media solutions which shows the great influence of the solvation effect on the acid-base equilibria. The good correlation between the pK _a values in aqueous and non-aqueous solutions enables the pK _a values in water to be estimated with sufficient accuracy, even in the cases when the experimental limitations make the determination impossible which is shown on the basis of selected examples.     

Novel colorimetric chemosensors containing pyridine moiety for detection of some cations in water and crops samples: Design,synthesis, and evaluation

This investigation deals with synthesis of some novel chemo sensors for identifying cations in drinking water and agricultural crops. This takes place via interaction of 2,5-dioxo-1,2,3,4-tertrahydropyridine-3-carbonitrile (3) and 2-thioxo-5-oxo-1,2,3,4-tertrahydropyridine-3-carbonitrile (4) with Cu^II and Co^II. The novel compounds' structures have been examined using spectrum data (IR, ¹H NMR, ¹³C NMR, and MS) as well as elemental and physical studies. Complexation behaviors of Compounds 3 and 4 as organic ligands were predicted, discussed, and calculated via Density-Functional Theory (DFT) and Colorimetric investigation. The newly synthesized receptors 3 and 4 showed selective colormetric sensing capability for some cations by color shifting from colorless to pale violet in a nearby ideal aqueous solution enabling naked eye identification and quantitative determination of cooper (Cu^II) and cobalt (Co^II) metal ion.     

Osmotic and activity coefficients of two macrocyclic aminals in aqueous solution at 288.15, 293.15, 298.15 and 303.15 K

The osmotic coefficients of 1,3,5,7-tetrazatricyclo (3.3.1.13,7) decane (HMT) and 1,3,6,8-tetrazatricyclo (4.4.1.13,8) dodecane (TATD) in aqueous solutions were measured at 288.15, 293.15, 298.15 and 303.15 K. The technique used was the isopiestic. The data were used to calculate the activity coefficients of the two solutes at the four temperatures. The few data points found for HMT in literature at 298.15 K agree well with the new data. The reinforcement of water structure by the two aminals is discussed.     

Measurement and prediction of infinite dilution activity coefficients for alkane in alkane within wide temperature

The infinite dilution activity coefficients of alkane (hexane, octane, decane and dodecane) in alkane (hexadecane and octadecane) were measured in the region of 313–470 K using a gas stripping method. The experimental results were predicted by the modified ASOG previously proposed.     

Good linear relationship between logarithms of Eigen’s water exchange constants for several divalent metal ions and activation energies of corresponding metal-catalyzed alkoxysilane hydrolysis in ethylene-propylene copolymer system

Catalytic efficiencies of seven divalent metal acetylacetonate complexes [M(acac)₂; M = Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II)] with respect to the water-crosslinking kinetics of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-VTMS) were investigated to examine the effects of progressive changes in metal ion using ATR-FTIR spectroscopy. The hydrolysis activation energies of EPR-g-VTMS follows the order: No catalyst ≈ Ni(acac)₂ > Co(acac)₂ > Fe(acac)₂ ≈ Zn(acac)₂ > Cd(acac)₂ ≈ Cu(acac)₂ > Pb(acac)₂. Interestingly, the kinetics results revealed that the plots of hydrolysis activation energies of EPR-g-VTMS containing M(acac)₂ complexes and Eigen’s water exchange constants for corresponding metal ions showed a excellent linear relationship, suggesting that the reaction pathway for the silane water-crosslinking with hydrous M(acac)₂ complex in EPR-g-VTMS system may be similar to that for water exchange of the metal ion in an aqueous system. Based on the knowledge of traditional kinetics studies by Eigen and Wilkins and hybrid sol-gel chemistry, the plausible catalytic mechanism for M(acac)₂ complexes in EPR-g-VTMS system was proposed.     

NaOH溶液中碱浓度、氧气压力以及温度对Pt电极上氧气还原反应的影响

设计制作一种新型耐压电化学池并采用循环伏安(CV)和线性扫描伏安(LSV)技术系统研究了碱浓度、氧气压力以及温度对NaOH溶液中氧气还原反应(ORR)的影响. 研究结果表明,碱浓度、氧气压力和温度对ORR动力学和热力学都有很大的影响. 随着碱浓度增大,ORR过程逐渐由2 电子(生成HO₂^-)转为1 电子(生成O₂^-)反应,并且由于氧气溶解度减小和体系粘度增大ORR过程受到很大抑制. 增大压力可以明显增加氧气溶解度,从而从动力学上促进ORR过程;同时计算得到了氧气在不同浓度NaOH溶液中的亨利系数. 随着介质温度升高,由于氧气反应活性增强、扩散系数增大和溶解度减小的共同作用,表现出在给定浓度下存在一最佳温度使得ORR峰电流达到最大.