The solubility of mercury vapor in water has been measured by means of atomic absorption spectrophotometry over the temperature range of 5–60°C under atmospheric pressure. The aqueous solubility obeys Henry’s law at each temperature. The solubilities and the Henry coefficients are reported. From the solubility data, the heat of the solution of mercury vapor in water is found to be −5.3 kcal/mol. The relationship between the Henry coefficient, k, and the solution temperature, T, is expressed by logk=−1078×1⁄T+6.250. From this equation, the solubilities at 70–100°C are estimated. The solubility of the mercury vapor in sea water has also been measured over the temperature range of 5–30°C. A salting-out effect on the solubility is observed. The practical application of the aqueous solubility of the mercury vapor is discussed from the analytical point of view.
Aqueous solubilities of benzene and of alkylbenzenes, toluene, ethylbenzene, propyl- and isopropylbenzene, (o-, m-, and p-) xylene, and (1,2,3-, 1,2,4-, and 1,3,5-) trimethylbenzene, have been measured. An apparatus is described which provides a convenient means of obtaining aqueous solutions saturated with solute vapor. The method involves introducing solute vapor, which is in equilibrium with a liquid solute, into water and circulating it in a closed system. This method has three principal advantages: (1) The solubility equilibrium can be attained within 3 min, (2) it can be determined whether the solubility obeys Henry’s law, and (3) based on Henry’s law, solutions of any desired concentrations of solute at a given temperature of water can be easily prepared.
The association constants of ferrocene with cyclodextrins (CyD’s) in an aqueous medium at 25 °C have been determined by solubility measurements of ferrocene in both the absence and presence of CyD. The solubility of ferrocene in pure water was found to be (4.25 ± 0.02) × 10−5 mol dm−3 at 25.0 ± 0.1 °C. The β- and γ-CyD’s form only 1 : 1 complexes with ferrocene. The 1 : 1 association constants were determined to be (1.39 ± 0.21) × 102 (α), (1.65 ± 0.04) × 104 (β), and (9.04 ± 0.11) × 102 dm3 mol−1 (γ). The 2 : 1 (CyD : ferrocene) association constant was (2.36 ± 0.06) × 103 dm3 mol−1 (α). Ferrocene-included CyD precipitates were also prepared in water, and their stability upon drying in air was studied. The sublimation enthalpy of ferrocene in the temperature range of 290.65 to 298.15 K was estimated to be 74.2 ± 1.5 kJ mol−1.
The complex formation of cyclodextrin (CyD, host) with C5 to C9 normal alkanes (guests) has been studied in aqueous medium at 25°C by making use of the volatilization rate of alkane molecules from aqueous into gaseous phase. In the excess of the host, β- and γ-CyDs form 1:1 complexes, while α-CyD forms 1:1 and 2:1 (host: guest) complexes. With an increase in the chain length of alkane, association constants for three CyDs increased; in the case of α-CyD, the 1:1 association constant for C9 was identical to that for C8, while the 2:1 association constant continued to increase. The cavity size of CyD, the alkane chain length, and hydrophobicity and surface area of alkane molecules were taken into account to discuss the host-guest inclusion mechanism.
Formation constants of the following aromatic hydrocarbons with α-,β-, and γ-cyclodextrin(CyD) were determined in aqueous medium at 25°C in the presence of excess CyD : benzene, toluene, ethylbenzene, propylbenzene, isopropylbenzene, (o-, m-, and p-)xylene, and (1,2,3-, 1,2,4-, and 1,3,5-)trimethylbenzene. The technique used to study association between host(CyD) and guest (hydrocarbon) is based on the facts that the guest molecules can be driven out to gaseous phase by introducing an inert gas at a constant flow rate into the aqueous solution and that the volatilization rate of guest decreases with increasing association with the host in the aqueous solution. The 1 : 1 and 2 : 1 (host : guest) formation constants were evaluated. As a measure of hydrophobicity of guest molecules, the free energy change of dehydration derived from Henry’s law constant was used. Based on hydrophobicity and a host-guest spatial-fitting model, the formation constants have been discussed.
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