G. Somsen

Enthalpies of solution of some tetraalkylammonium bromides in binary mixtures of water and some amides

Enthalpies of solution of tetraethylammonium bromide in mixtures of N,N-dimethylformamide (DMF) and water and of tetramethylammonium bromide in mixtures of DMF and water, N-methylformamide (NMF) and water, formamide (F) and water, and of NMF and F have been measured calorimetrically at 25°C in the whole mole-fraction range. The enthalpies of solution of tetraethylammonium bromide in DMF-water reach a maximum value while the enthalpies of solution of tetraethylammonium bromide in this mixture show a flat, broad maximum and a minimum. A similar behavior is found in NMF-water and F-water mixtures. In the NMF-F system the enthalpies of solution display a nearly ideal behavior. The results are compared with those of tetra-n-butylammonium bromide and of tetra-n-propylammonium bromide.

Excess and apparent molar volumes of mixtures of water and acetonitrile between 0 and 25°C

From densities measured at 0, 1, 2.5, 5, 10 and 25°C of mixtures of water and acetonitrile, the excess molar volumes and the apparent and partial molar volumes of both components have been derived as a function of mixture composition. Contrary to results on enthalpies of solution in mixtures of water and acetonitrile, the values obtained do not show substantial changes around 0.7 mole fraction of water. At this composition and at low temperatures, the excess molar volumes exhibit a rather flat minimum and the apparent and partial molar volumes of water show an inflection.

Enthalpies of solution of tetra-n-butylammonium bromide in binary mixtures of water, formamide, N-methylformamide, and N,N-dimethylformamide

The enthalpies of solution of tetra-n-butylammonium bromide have been measured in mixtures of formamide (F) with water, N-methylformamide (NMF) with water, N,N-dimethylformamide (DMF) with water, F with NMF, DMF with F, and NMF with DMF at 25°C in the whole mole-fraction range. The enthalpies of solution vs composition profiles show a maximum value in the DMF-H2O and in the DMF-F systems. In the F-NMF and NMF-DMF mixturesn-Bu4NBr displays a nearly ideal behavior, whereas in the other solvent systems the excess enthalpy of solution deviates substantially from zero.

Heat capacities and volumes of some polybasic carboxylic acids in water at 298.15 K

Abstract Heat capacities divided by volume of aqueous solutions of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, dl -malic acid, l -(+)-tartaric acid, and citric acid have been measured using flow calorimetry at 298.15 K. Employing densities of the above mentioned solutions, determined with a vibrating-tube densimeter, we obtained partial molar heat capacities at infinite dilution.

Enthalpies of solution and heat capacities of tetra-n-butylammonium bromide in several solvents from 278 to 328 K

Enthalpies of solution of tetra- n -butylammonium bromide have been measured calorimetrically in formamide, in N -methylformamide, and in N,N -dimethylformamide from 278 to 328 K, and in N -methylacetamide from 308 to 328 K at 10 K intervals. In addition the molar heat capacity of crystalline tetra- n -butylammonium bromide has been determined. Application of the integral enthalpy method to these results and to Sarma and Ahluwalias results in water yields partial molar heat capacities at infinite dilution, C ∞ p , 2 , in the various solvents from 278 to 328 K. In formamide, in N -methylformamide, in N -methylacetamide, and in N,N -dimethylformamide, C ∞ p , 2 ( n -Bu 4 NBr) values are mutually comparable but much smaller than in water.

Hydrophobic hydration in mixtures of N,N-dimethylformamide and water enthalpies of solution and heat capacities of tetra-n-butylammonium bromide

Abstract Enthalpies of solution of tetra- n -butylammonium bromide have been measured calorimetrically in mixtures of N,N-dimethylformamide ( dmf ) + water from 278 to 328 K at 10 K intervals covering the whole mole fraction range. All profiles of enthalpy of solution against composition show endothermic maxima. From a simple hydration model it is possible to calculate the number n of water molecules which surround a hydrophobic alkyl group and the enthalpic effect of hydrophobic hydration in pure water. The latter effect appears to decrease strongly with temperature, while n is almost temperature independent. In addition partial molar heat capacities, C p ,2 ∞ , of n -Bu 4 NBr have been calculated in the dmf + water mixtures; C p ,2 ∞ hardly changes in the range from 0 to 0.6 mole fraction of water. In more water-rich regions C p ,2 ∞ increases very rapidly towards its value in pure water.

Enthalpies of solution of amides and peptides in aqueous solutions of urea and in N,N-dimethylformamide at 298.15 K

Abstract Enthalpies of solution into water of formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, N-acetylglycinamide, N-acetyl-L-alaninamide, N-acetyl-L-leucinamide, N-acetyl-L-prolinamide, N-acetyl-N′-methylglycinamide, N-acetyl-N′-methyl-L-alaninamide, N-acetyl-N′-methyl-L-leucinamide, and N-acetyl-N′-methyl-L-prolinamide, have been measured calorimetrically at 298.15 K. In addition, the enthalpies of solution at the same temperature of all the above into (urea + water), and of the amino-acid amides into the solvent N,N-dimethylformamide, have also been obtained.

Enthalpic pair-interaction coefficients between electrolytes and non-electrolytes in water and N N-dimethylformamide

From the enthalpies of solution of various electrolytes and some non-electrolytes in binary solvent systems containing water and different amides, several enthalpic pair-interaction coefficients have been evaluated. They refer to the interactions of different quarternary ammonium bromides, some trialkyl-phosphates and triethylamine with formamide, N-methylformamide, N N-dimethylformamide and N N-dimethylacetamide in aqueous solution and with water in the non-aqueous solvent N N-dimethylformamide. In aqueous solution a much larger variety of values for pair-interaction coefficients is found than in the non-aqueous systems. The different pair-interaction coefficients in water can be related to the structure of the solutes. A functional group additivity concept, introduced by Savage and Wood for non-ionic solutes, is also applicable to the interactions between electrolytes and non-electrolytes. The values of the functional-group parameters for the electrolytes in water are in reasonable agreement with those obtained from non-electrolytic interactions. In non-aqueous solutions the additivity concept gives a better correlation of the experimental values than in aqueous systems.

Enthalpies of Solution of Urea in Binary Mixtures of Water and some Amides at 25°C

Enthalpies of solution of urea have been measured in water, formamide (F), iV-methylformamide (NMF), and A^iVdimethylformamide (DMF) and in binary mixtures of these solvents at 25 °C. The enthalpies of solution in the pure solvents all are endothermic increasing in the sequence DMF < NMF < F < H20. The difference in the enthalpic behaviour of the tetraalkylammonium bromides between amide—water and amide—amide mixtures is not present for the solute urea. Mutual comparison of the results shows that the interactions of urea with water and with the amides are of the same order of magnitude.

Solvation of tetra-alkylammonium bromides in N-methylformamide and N-methylacetamide. The enthalpic effect of “hydrophobic” interaction

Abstract Enthalpies of solution of tetra-alkylammonium bromides (R 4 NBr, R = methyl, ethyl, n -propyl, and n -butyl) in N-methylformamide and N-methylacetamide have been determined calorimetrically. The corresponding enthalpies of transfer to water deviate substantially from those of the alkali bromides and can be explained by means of the specific interactions of R 4 N + ions with water. In order to evaluate the contributions of the single cations, an approach has been introduced which relates the enthalpies of solvation of both alkali bromides and tetra-alkylammonium bromides in N-methylformamide, N-methylacetamide, water, formamide, and methanol with those in propylene carbonate. The results indicate that the enthalpies of solvation of tetra-alkylammonium ions in water and methanol (and perhaps in formamide) include an effect which is correlated with “hydrophobic” (or “solvophobic”) interaction. This enthalpic effect is not present in N-methylformamide or N-methylacetamide.