G. Roux-Desgranges

Heat capacities and densities of mixtures of very polar substances 1. Mixtures containing acetonitrile

Excess molar heat capacities CEp, m at constant pressure and excess molar volumes VEm have been determined, as a function of mole fraction X at 298.15 K and atmospheric pressure for the eight liquid mixtures: {xCH3CN + (1 − x)C6H6}, {xCH3CN + (1 − x)1,4-C4H8O2}, {xCH3CN + (1 − x)N(C2H5)3}, {xCH3CN + (1 − xCHCl3}, {xCH3CN + (1 − x)(CH3)2CHOCH(CH3)2}, {xCH3CN + (1−x)CH3COCH3}, {xCH3CN + (1−x)HCON(CH3)2}, and {xCH3CN + (1 − x)(CH3)2SO}. The dipole moment of acetonitrile is p/(10−30·C·m) = 13.2, while for the second components p/(10−30·C·m) ranges form 0 for benzene to 13.2 for dimethylsulfoxide. The instruments used were a Picker flow microcalorimeter and a vibrating-tube densimeter, respectively. The CE p, ms are negative and small for {xCH3CH + (1−x)1,4-C4H8O2}, {xCH3CN + (1−x)HCON(CH3)2}, and {xCH3CN + (1−x)(CH3)2SO}; S-shaped (and small) for {xCH3CN + (1−x)C6H6} and {xCH3CN + (1−x)CH3COCH3}; and positive and quite large for {xCH3CN + (1−x)(CH3)2CHOCH(CH3)2}, {xCH3CN + (1−x)CHCl3}, and {xCH3CN + (1−x)N(C2H5)3} (at x = 0.5, CEp, m = 6.04 J·K−1·mol−1 for the last mixture). VEm VEm{xCH3CN + (1−x)C6H6} shows an S-shaped composition dependence, with the positive part extending from about x = 0.63 to pure benzene. All the other excess volumes are negative and rather small.

Heat capacities and densities of mixtures of very polar substances. 3. Mixtures containing either trichloromethane or 1,4-dioxane or diisopropylether

Excess molar heat capacities CPE at constant pressure and excess molar volumes VE have been determined, as a function of mole fraction x1 at 25°C and atmospheric pressure, for 10 binary liquid mixtures containing either trichloromethane (series I) with C6H5CH3, or C6H5Cl, or C5H5N, or CH3COCH3, or C6H5NO2; 1,4-dioxane (series II) with (C2H5)3N, or (CH3)2CHOCH(CH3)2, or (CH32SO); or diisopropyl ether (di-1-methylethyl ether) (series III) with (C2H5)3N, or CHCl3. The dipole momentsp (10−30C-m) of the substances range from nearly 0 to 14.1 for nitrobenzene. The CPE of series I and III are all positive, with CPE(x1=0.5) (J-K−1-mol−1) ranging from 1.04 for {x1CHCl3+x2C6H5Cl} to 16.66 for {x1(CH3)2CHOCH(CH3)2+x2CHCl3}. In series II, the CPE are positive and small for {x11,4-C4H8O2+x2(CH3)2CHOCH(CH3)2}, S-shaped and small for {x11,4-C4H8O2+x2(C2H5)3N}, and negative and small for {x11,4-C4H8O2+x2(CH3)2SO}. The excess volumes are small and positive for {x1CHCl3+x2C6H5CH3}, S-shaped for {x1CHCl3+x2CH3COCH3}, {x11,4-C4H8O2+x2(C2H5)3N} and {x1(CH3)2CHOCH(CH3)2+x2(C2H5)3N}, and negative for the other systems.

Limiting Partial Molar Excess Heat Capacities and Volumes of Selected Organic Compounds in Water at 25°C

Well-known Picker flow microcalorimeters for the differential measurements of volumetric heat capacities have been employed in conjunction with vibrating tube densimeters to determine the molar heat capacity, volume, and the apparent properties in dilute aqueous solutions for 17 organic solutes of moderate hydrophobicity. The dependence on concentration of the apparent properties allowed the limiting partial molar quantities at infinite dilution to be extrapolated and the limiting partial molar excess quantities to be evaluated. Comparison with available literature data shows good agreement. The application of group contribution rules to the limiting partial properties has been tested using the original method and parameters proposed by Cabani et al. The predicted values of the partial molar volumes are in fair agreement with the present data except for some less common solutes. With partial molar heat capacities, the agreement is less satisfactory. To improve the performance of the method, missing parameters for some types of monofunctional and bifunctional molecules have been evaluated.

EXCESS MOLAR HEAT CAPACITIES AND EXCESS MOLAR VOLUMES OF SOME MIXTURES OF PROPYLENE CARBONATE WITH AROMATIC HYDROCARBONS

Excess molar volumes VE and excess molar heat capacities CPE at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C4H6O3; PC) + benzene (C6H6;B), + toluene (C6H5CH3;T), + ethylbenzene (C6H5C2H5;EB), and + p-xylene (p-C6H4(CH3)2;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: VE (cm3-mol−1) at the minimum ranges from about −0.31 at x1=0.43 for {x1C4H6O3+x2p-C6H4(CH3)2}, to −0.45 at x1=0.40 for {x1C4H6O3+x2C6H5CH3}. For the systems (PC+T), (PC+EB) and (PC+p-X) the CPEs are all positive and even more skewed. For instance, for (PC+T) the maximum is at x1,max=0.31 with CP,maxE=1.91 J-K−1-mol−1. Most interestingly, CPE of {x1C4H6O3+x2C6H6} exhibits two maxima near the ends of the composition range and a minimum at x1,min=0.71 with CP,minE=−0.23 J-K−1-mol−1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents: IV. HE, VE and CEP with 2-methoxyethanol at 298.15 K1

Abstract Molar excess enthalpies H E , molar excess volumes V E and molar excess heat capacities C E p of mixtures of 2-methoxyethanol (1) with 2-ethoxyethanol (2), 2-butoxyethanol (2) and 2-(2-methoxyethoxy)ethanol (2) and H E of mixtures of 2-methoxyethanol (1) with 2-(2-ethoxyethoxy) ethanol (2) and 2-(2-butoxyethoxy)ethanol (2) were determined as a function of composition at 298.15 K and atmospheric pressure. As expected, owing to the similar chemical nature of the components, the excess functions of these mixtures are relatively small.

Molar heat capacities and volumes of transfer of cytosine, thymine, caffeine and 1,3-diethylthymine to aqueous solutions of glycyl-glycine and L-α-alanyl-L-α-alanine at 25°C

Densities and specific heat capacities of ternary aqueous systems containing dipeptides (glycyl-glycine or L-α-alanyl-L-α-alanine) and nucleic acid bases (cytosine or thymine) or their alkyl derivatives (1,3-diethylthymine or caffeine) were determined at 25°C by flow calorimetry and flow densimetry. The partial molar volumes and heat capacities of transfer at infinite dilution of the different nucleic acid bases from water to water+dipeptide solutions were obtained therefrom. Except for the case of the transfer of cytosine to aqueous glycyl-glycine solutions where a small positive dependence of the transfer quantities was observed with the dipeptide concentration, the values of the heat capacities of transfer were in general low, positive or negative, depending on the compensation of hydrophobic-hydrophilic interactions between the dipeptide and the base. The volumes of transfer of most of the bases are very small, within the limit of the experimental error.

Excess molar heat capacities and enthalpies for 1-alkanol + n-alkane binary mixtures. New measurements and recommended data

Abstract Excess molar heat capacities at constant atmsopheric pressure C p E have been determined at 298.15 K as a function of the alcohol mole fraction x, for the following binary mixtures : ethanol + n-hexadecane, 1-butanol + n-decane, and 1-hexanol + n-hexane. The instrument used was a Picker flow calorimeter. The densities p for these mixtures at the same pressure and temperature were measured with a vibrating-tube densimeter ; the corresponding molar excess volumes V E were calculated therefrom. For the same mixtures as well as for the two other mixtures methanol + n-heptane and ethanol + n-heptane a complete literature search has yielded a selection of both the excess molar heat capacities and enthalpies H E . Several selected sets of data have been critically analyzed in terms of quality of measurements and precision. The best sets of data have been combined together and, also whenever possible, with our present experimental data to produce recommended data sets of the two calorimetric properties for the five binary mixtures, then considered as key-systems. In the course of this work particular attention was paid to keep data points in the whole concentration range especially in the dilute regions. Finally for each above mixture the recommended values of C E p and H E have been fitted accordingly with the same type of smoothing equation.

Apparent molar heat capacities and volumes of some alkylated derivatives of uracil and adenine in aqueous solution at 25°C

Densities and apparent molar heat capacities of some alkylated derivatives of uracil and adenine: 1-methyluracil, 1,3-dimethyluracil, 1,3-diethylthymine, 5,6-trimethylene-1,3-dimethyluracil, 5,6-tetramethylene-1,3-dimethyluracil, 5,6-pentamethylene-1,3-dimethyluracil, 2,9-dimethyladenine, 2-ethyl-9-methyladenine, 2-propyl-9-methyladenine, 8-ethyl-9-methyladenine, 6,8,9-trimethyladenine and 8-ethyl-6,9-dimethyladenine were determined using flow calorimetry and flow densimetry at 25°C. It was found that the partial molar volumes and heat capacities correlate linearly with the number of substituted methylene groups-CH2-as well as to the number of hydrogen atoms, nH, belonging to the skeleton of the molecule. In the case of alkylated uracils a difference was observed in the values at infinite dilution V2o and Cp2o, depending on the substitution of alkyl and cyclooligomethylene groups.

Apparent molar heat capacities and volumes of electrolytes and ions in acetonitrile-water mixtures

Apparent molar volumes Vφ and heat capacities Cp,φ of NaCl, KCl, KNO3, AgNO3, KI, NaBPh4 and Ph4PCl have been measured in acetonitrile (AN)-water mixtures up to xAN=0.25 by flow densitometry and flow microcalorimetry. Limited data have also been obtained for NaF, LiCl and KBr up to xAN=0.15. Single ion volumes and heat capacities of transfer were obtained using the assumption ΔtXφ(PH4P+) = ΔtXφ(BPh4-) where X=V or Cp and ΔtXφ is the change in Xφ for a species on transfer from H2O to AN-H2O mixtures. Volumes and heat capacities for simple salts show relatively little dependence on solvent composition. However, ΔtXφ for simple ions show more pronounced variations, exhibiting at least one extremum. These extrema are similar to but much less pronounced than those derived previously for ions in t-butanol-water mixtures. Surprisingly little correlation is found between the present data and other thermodynamic transfer functions. This is attributed to the predominance of ion-solvent over solvent-solvent interactions in AN-H2O solutions. ΔtVφ and ΔtCp,φ for the silver ion differ markedly from those of the alkali metal ions as a result of the well-known specific interaction between Ag+ and AN.

THERMOCHEMISTRY OF AQUEOUS SOLUTIONS OF ALKYLATED NUCLEIC ACID BASES. Part VII. Apparent molar heat capacities and volumes of aqueous solutions of alkylated derivatives of uracil at 298.15 K

Abstract Densities and heat capacities of some alkylated derivatives of uracil (1,3,6-tnmethyluracil, 1,3-dimethyl-6-ethyluracil, 1,3-dimethyl-6-propyluracil and 1,3-dimethyl-6-butyluracil) in dilute aqueous solutions are measured using flow calonmetry and flow densimetry at 298.15 K. Apparent molar volumes and heat capacities were derived and analyzed as a function of concentration.