Unexchangeable Interlayer Anions; Synthesis and Characterization of Zn/Al- and Mg/Al-Layered Double Hydroxides with Interlayer Alizarin red S

The formation of complexes between -cyclodextrin and 1-alkanols hasbeen studied calorimetrically at 298 K in water and in concentrated aqueoussolutions of ethanol or urea. When a complex is formed, calorimetry enables thecalculation of both the enthalpy and the association constant, from which thefree energy and the entropy of the process can be obtained. The effects ofethanol and urea on the hydration cospheres of the interacting substances havebeen investigated through the study of the binary solutions of the involvedsolutes in water and in the mixed solvents. The findings obtained are, then,related to the consequent changes in the association parameters.The forces involved in the association process are discussed in the light of the signsand values of the thermodynamic parameters obtained. The most important featurescoming out from this study are: (i) association in water is an entropy-driven process;(ii) in concentrated aqueous solutions of cosolvent, the enthalpic term contributessignificantly to the Gibbs energy, while the entropic contribution is smaller; (iii) forevery solvent medium employed, the invariance of the entropic contribution withincreasing alkyl chain length of the alkanol is an indication that the relaxation ofwater molecules from the cavity of the macrocycle mainly determines the associationprocess.     

9,10-Dicyanoanthracene photosensitized oxidation of aryl alkanols: evidence for an electron transfer mechanism

9,10-Dicyanoanthracene (DCA) photosensitizes the oxidation of a series of para substituted aryl alkanols in oxygen-saturated acetonitrile. Product analysis and Hammett correlations support an electron transfer mechanism for the title reaction.     

Ultrasonic velocity and apparent isentropic compressibilities in mixtures of nonelectrolytes

Ultrasonic velocities have been determined for binary mixtures of pyridine + n-alkanol (C₁-C₁₀) over the whole composition range at 25‡C. The excess isentropic compressibilities K _S ^E and apparent molar isentropic compressibilities K_Φ,s are estimated from these measurements. The K _S ^E values are negative for all the systems over the complete mole fraction range except pyridine + decanol for which small positive values are obtained. The standard partial molar isentropic compressibilitiesK‡ of the alkanols are positive and increase linearly with the chain length of the alkanol molecules. It indicates that a methylene functional group makes a positive contribution to the expansion coefficient of a solute in these mixtures.     

Effect of intramolecular cyclization on the enthalpies of solvation of tetramethylurea in water and alkanols at 298.15 K

The enthalpies of solution of N,N′-dimethylethyleneurea (1,3-dimethyl-2-imidazolidinone) in water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol (2-methyl-2-propanol) were measured calorimetrically at 298.15 K. For comparison purposes, the previous data on enthalpic effects of 1,1,3,3-tetramethylurea dissolution (solvation) in the same solvents were analyzed. It has been concluded that the intramolecular cyclization of tetramethylurea, to form dimethylethyleneurea, results in strengthening of the solute solvation and this tendency is more pronounced in a non-aqueous (alcoholic) medium.     

An improvement for the excess enthalpy prediction by UNIFAC. 1. Binary mixtures containing alkanes

The UNIFAC model is tested for its ability to correlate and predict binary excess enthalpies. Besides the alkanes containing systems from earlier work, those for ester-alkane mixtures are also investigated. The model is fitted to binary excess enthalpy data. The influence of group surface area parameters is also examined by using values based on the van der Waals surface areas Q_s multiplied for all the groups by the factor n. A significant improvement of H^E calculation in most of the systems considered is observed if the factor n is taken equal to 3.     

Excess volumes and viscosities of mixtures of dimethylsulfoxide with normal alcohols at 40°C

Excess volumes and viscosities have been determined for DMSO + n-hexanol, + n-heptanol, + n-octanol, and + n-decanol at 40°C. The excess partial molar volumes V ₁ ^E , changes in viscosities , the parameter d of the Grunberg and Nissan expression, and excess Gibbs free energies of activation of flow G _* ^E have been calculated from the experimental data. All the excess volumes are positive over the whole composition range, with V ^E increasing with the length of the alkanol chain. V ^E results are discussed in terms of disruption of alkanol multimers, weakening of interactions between DMSO molecules, influence of interactions between components, and structural effects. The V ^E data have also been analyzed using the Prigogine-Flory-Patterson expression which separates V ^E into three contributions. Correlation is also observed between the sign of and V ^E for all the mixtures studied.     

Isentropic Compressibility Changes of Mixing for 1,3-Dioxolane or 1,4-Dioxane + Water + Propanol Ternary Mixtures

Speed of sound data, u_ijk, of 1,3-dioxolane or 1,4-dioxane(i) + water(j) + propan-1-ol or propan-2-ol(k) ternary mixtures and their sub-binary mixtures, u_ij, of 1,3-dioxolane or 1,4-dioxane(i) + water or propan-1-ol or propan-2-ol(j) and water(i) + propan-1-ol or propan-2-ol(j) mixtures have been measured over the entire composition range at 308.15 K. Isentropic compressibility changes of mixing, (κ_s^E)_ij and (κ_s^E) _ijk, for the binary and ternary mixtures have been determined by employing the observed speeds of sound data and densities (calculated from their molar excess volumes data). The (κ_s^E) _ij and (κ_s^E) _ijk values have also been predicated by the graph theoretical approach and the Flory theory. It has been observed that (κ_s^E) _ij and (κ_s^E) _ijk predicted by the graph theoretical approach compare well with their corresponding experimental values.     

Enthalpies of solution of 1,1,3,3-tetramethylurea in normal and branched alkanols (C2-C4) at 298.15 K

The enthalpies of solution were determined for 1,1,3,3-tetramethylurea in ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol (2-methyl-2-propanol). Measurements were made at 298.15 K and molalities m ≅ (0.007 to 0.036) mol · kg⁻¹ with a precise isoperibol ampoule-type calorimeter. Standard enthalpies of solution and transfer from one alkanol to the other (including methanol) were calculated. The obvious relationship between the enthalpic and volumetric effects of solution of tetramethylurea in the n-alkanols (C₁-C₄) was discovered. The enthalpic effects of transfer caused by branching of the alkanol molecules, 1-propanol → 2-propanol, and 1-butanol → t-butanol, are opposite in sign and dominated by the configurational changes in the solvation environment of tetramethylurea.