Enthalpy of dilution of aqueous mixtures of amides,sugars, urea,ethylene glycol,and pentaerythritol at 25°C: Enthalpy of interaction of the hydrocarbon,amide, and hydroxyl functional groups in dilute aqueous solutions

The enthalpy of dilution of all one-and two-solute aqueous mixtures of a series of compounds were measured from about 0.2 to 2.0 mole-kg^–1 at 25°C. The compounds included in the study wereN-methylformamide,N-methylacetamide,N-methylpropionamide,N-butylacetamide, urea, ethylene glycol, pentaerythritol, glucose, and sucrose. The results of the enthalpy measurements were used to calculate the pairwise enthalpy of interaction for each compound with all the other compounds. A simple additivity principle is used to correlate the data. The principle assumes that each functional group on one molecule interacts with every functional group on the other molecule and that each of these interactions has a characteristic effect on the enthalpy that is independent of the positions of the functional groups in the two molecules. The resulting equation gives a rough but useful correlation of the results. Of the six interactions between the CH₂, CONH, and CHOH functional groups, the CONH–CONH interaction is the strongest, the CHOH–CHOH interaction is the weakest, and the CH₂–CH₂ interaction is about equal in magnitude to the rest of the interactions. Thus, the CH₂–CH₂ and CONH–CONH are not the only interactions making important contributions to the enthalpy of a wide variety of systems.     

Enthalpies of dilution of aqueous solutions of amides and alcohols

Enthalpies of dilution of aqueous systems containing formamide, dimethyl-formamide, the mixture of these amides, and each amide separately with mannitol, inositol, and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and in combination with literature data. New values for the methylene-amide, carbinol-amide, and amide-amide group interaction enthalpies are presented. These may be used with data on a wider variety of solute systems to obtain interaction enthalpies for new groups.     

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine and other nonelectrolytes

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine, alone and in ternary system with each of mannitol, myoinositol, cyclohexanol, formamide, dimethylformamide, and trioxane have been determined. The data have been treated in terms of the Savage-Wood additivity principle and first estimates for the pairwise groups interaction enthalpies of N/N, CH₂/N, CHOH/N, COHN/N and –O–/N have been made. The results are discussed in light of all other known group interaction enthalpies. The limitations and utilities of the Savage-Wood principle are reviewed.     

Enthalpy of dilution of aqueous systems containing S-trioxane and some amides. Analysis of the interaction of saccharides with amides in aqueous media

Enthalpies of dilution of aqueous systems of trioxane+formamide and trioxane+dimethylformamide have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle, and a first estimate of the pairwise group interaction enthalpy for-O-/CONH is presented. Systems of saccharides and amides are not amenable to the Savage-Wood treatment used in recent works. However, when treated in conjunction with all available data to yield a different set of group interaction parameters, saccharides behave more predictably. Implications of this state of affairs are considered.     

Enthalpies of dilution of N,N-dialkylformamides dissolved in formamide,N-methylformamide,and N-methylacetamide

The enthalpies of dilution of N,N-dimethylformamide, N,N-diethylformamide, N,N-dipropylformamide, N,N-dibutylformamide, and N,N-dipent-ylformamide dissolved in formamide, N-methylformamide, and N-methylacetamide have been measured calorimetrically. From these, enthalpic interaction coefficients have been calculated, which were interpreted also in terms of an additivity model.     

Enthalpies of dilution of urea solutions in six polar solvents at several temperatures

Using the isothermal displacement calorimeter, enthalpies of dilution are obtained for solutions of urea in water, methanol, ethanol, formamide, N,N-dimethyl-formamide, and dimethyl sulfoxide. The results are discussed in terms of solute-solvent and solute-solute interactions.Now Diane Beaumont.     

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type. A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented. It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aqueous butanediol isomers and 1-hexanol were very large. Molar enthalpies of infinite dilution of aqueous poly-alcohol (cyclohexaamylose) were endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enthalpies of mixing of aqueous solutions of the amino acids glycine,l-alanine and l-serine

The enthalpies of mixing of aqueous solutions of the three amino acids glycine, L-alanine and L-serine have been determined at 25°C. These data have been analyzed, using the McMillan-Mayer theory, to obtain the various enthalpic pair interaction coefficients, h_xy. The results are discussed in terms of the likely molecular interactions. The application of the Savage-Wood additivity principle to these solute systems is also considered.     

Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.     

Enthalpies of interaction of glycine with some amides in aqueous solutions at 298.15 K

The dissolution enthalpies of glycine in aqueous solutions of acetamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylformamide, N,N-diethylformamide and N,N-diethylacetamide were measured at 298.15 K. The enthalpic pair interaction coefficients of glycine zwitterion-amide molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions of amides. The additivity of groups concept of Savage and Wood was used to estimate the contribution of each of the functional groups of the studied amides.     

Enthalpies of dilution of electrolyte solutions by flow microcalorimetry

The enthalpies of dilution of NaCl, Me₄NBr, andn-Bu₄NBr were measured in water at 25°C with a new flow microcalorimeter. The data were analyzed with a polynomial equation, and the derived relative apparent molal enthalpies _L are in good agreement with literature values. Provided care is taken that mixing is complete, flow calorimeters are as reliable and much less time-consuming than cell-type instruments for enthalpies of dilution measurements.     

Enthalpies of transfer of amino acids from water to aqueous solutions of formamide

Enthalpies of solution of glycine, l-alanine, l-serine in water and aqueous solutions of formamide were measured at 298.15 K. Transfer enthalpies of amino acids from water to aqueous solutions of formamide were derived and interpreted qualitatively with hydration co-sphere overlap model. The results show that the structure interaction between formamide and zwitterionic head-group and hydrophilic side chain of amino acids make a negative contribution to transfer enthalpy, while that with the hydrophobic side chain is positive. In the solvent composition range studied, transfer enthalpies decrease overall with the increasing concentration of formamide, with the relative order of l-serine < glycine < l-alanine.     

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.     

Interactions of ether groups with saccharides. Enthalpy of dilution of aqueous systems containing S-trioxane and inositol,mannitol, or cyclohexanol

Enthalpies of dilution of aqueous systems containing trioxane, and trioxane with each of mannitol, inositol and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and, in conjunction with literature data on ether compounds a revised estimate of the pairwise group-interaction enthalpy for CH₂/–O– and a first estimate for CHOH/–O– are presented. Systems of saccharides and saccharides with alcohols do not conform to the Savage-Wood principle and an explanation in terms of the specific hydration properties of saccharides is offered.     

Density functional studies of molecular structures of N-methyl formamide, N,N-dimethyl formamide, and N,N-dimethyl acetamide

Density functional theory was applied to the calculation of molecular structures of N-methyl formamide (NMF), N,N-dimethyl formamide (DMF), and N,N-dimethyl acetamide (DMA). DFT calculations on NMF, DMF, and DMA were performed using a combination of the local functional of Vosko, Wilk, and Nusair (VWN) with the nonlocal exchange functional of Becke and the nonlocal correlational functional of Lee, Yang, and Parr (BLYP). The adiabatic connection method (ACM) of Becke has also been used, for the first time, for the calculation of molecular structures of NMF, DMF, and DMA. The calculated molecular structures are in excellent agreement with the experimental geometries of NMF and DMA derived from gas-phase electron-diffraction studies. Sparse experimental data on the gas-phase geometry of DMF reported in the literature compares well with the DFT results on DMF. DFT emerges as a powerful method to calculate molecular structures.     

Enthalpies of dilution of aqueous electrolytes: The NaCl/H2O system

Analysis of enthalpy of dilution data for the system NaCl/H₂O at 298.15°K with correlating equations presently in widespread use shows that these do not satisfactorily fit the data at the lowest available concentrations. A new approach based on the extended Debye-Hückel theory is suggested. It is shown that a plot of the ratio of the apparent molar enthalpy of dilution to the change in ionic strength, L/I, versus (I _i ^1/2 –I _f ^1/2 )/I, should give a straight line at low enough concentration with a slope 2S _H/3. The intercept is related to the Debye distance parameterA and the coefficient of the first virial correction term. The quantityS _H is the limiting Debye slope as calculated from the properties of the pure solvent. These expectations are substantiated by the fits. Values of the parameters are compared with older estimates, and it is concluded that the choiceA=0 is reasonable.     

Enthalpic interactions of -alanine and -serine in aqueous urea solutions

The enthalpies of dilution of -alanine and -serine in various aqueous urea solutions have been determined by flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous urea solutions have been calculated according to the excess enthalpy concept. The results were interpreted from the point of view of solute–solute interactions moderated by solvent effects.     

Enthalpies of dilution of aqueous tetradecyltrimethylammonium bromide from 50 to 175°C

Enthalpies of dilution of aqueous tetradecyltrimethylammonium bromide have been measured from 0.3 to about 0.002 mol-kg^–1 and from 323 to 448 K at 1.03 MPa. Different methods of obtaining the enthalpy of micellization from experimental data are examined. Enthalpies of micellization calculated from these methods disagree by large amounts. From consideration of the temperature dependence of the average aggregation number and multiple equilibria equations for micellization, it is shown that there is an enormous dependence of micellizaton enthalpy on aggregation number of a micelle.     

Enthalpies of dilution from 50 to 225°C of aqueous decyltrimethylammonium bromide

Enthalpies of dilution of aqueous decyltrimethylammonium bromide have been measured from 0.56 to about .005 mol-kg^–1 and from 50 to 225°C near the saturation pressure of water using a flow calorimeter. The changes of the stoichiometric osmotic and activity coefficients with temperature, the excess apparent molar heat capacity, and the apparent and partial relative molar enthalpies have been calculated from the data.     

Enthalpies of Dilution of Colchicine in Aqueous NaCl Solutions

The concentration effect on the dilution enthalpies (Δ_dil H _m) of colchicine (COL) in aqueous NaCl solutions has been investigated by isothermal titration microcalorimetry at 298.15 K. The corresponding homogeneous enthalpic interaction coefficients have been calculated according to the excess enthalpy concept. The results show that the dilution enthalpies of COL in aqueous NaCl solutions at different mass fractions are positive. The overall trend is that enthalpies of dilution become more positive with the increase of the salt mass fraction. The values of enthalpic pair-wise interaction coefficients, h ₂, have been obtained by fitting the data of the enthalpies of dilution with a viral expansion. The results can be interpreted from the view of solute-solute and solute-solvent interactions involved in the solvent effects.