Showing papers in "Journal of Solution Chemistry in 1973"

Structure in aqueous solutions of nonpolar solutes from the standpoint of scaled-particle theory

Abstract: Underlying assumptions have been examined in scaled-particle theory for the case of a rigid-sphere solute in liquid water. As a result, it has been possible to improve upon Pierotti’s corresponding analysis in a way that explicitly incorporates measured surface tensions and radial-distribution functions for pure water. It is pointed out along the way that potential energy nonadditivity should create an orientational bias for molecules in the liquid-vapor interface that is peculiar to water. Some specific conclusions have been drawn about the solvation mode for the nonpolar rigid-sphere solute.

Studies of hydrophobic bonding in aqueous alcohols: Enthalpy measurements and model calculations

Abstract: The coefficients which measure the contribution of a pair of solute molecules to the excess enthalpy have been measured in water at 25°C for all pairs of alcohols which can be formed from the series methyl to n-butyl plus t-butyl as well as for ethanol with some of the higher alcohols and with the n-alkyl sulfonates through octyl. The methylene-group contribution to these coefficients is readily identifiable in suitable cases. These data and the corresponding free-energy and volume coefficients, where they are known, are analyzed in terms of amodel which specifies the core repulsion and solvation-layer overlap terms in the potential for the interaction of two solute molecules. The latter term has an adjustable parameter, the so-called Gurney free-energy parameter which is adjusted for each solute pair to fit the free-energy data. Its temperature and pressure derivatives are adjusted to fit the enthalpy and volume data, respectively. These parameters are compared with the corresponding thermodynamic coefficients of solvation as far as possible.

Enthalpies of alkyl sulfonates in water, heavy water, and water-alcohol mixtures and the interaction of water with methylene groups

Abstract: The heats of solution of the sodium n-alkyl sulfonates from methyl to octyl have been measured at 25°C in water, D2O, and three alcohol-rich mixtures with water, all at solute concentrations low enough so that solute-solute interaction is negligible. Methylene-group contributions to the enthalpies of transfer are readily identified. Collation with the results of earlier studies of enthalpies of transfer leads to the conclusion that methylene-group enthalpies of transfer can be identified as follows: 0.87 kcal-mole−1 for transfers to the gas phase from water and −0.035 kcal-mole−1 for transfers to D2O from H2O, independent of the solute type provided only that methylene-group contributions can be identified in the data. Compared to other solvents, water is about as lipophilic as dimethylsulfoxide or a mixture of 27 moles of water with 73 moles of methanol. However, the range of the interactions between different groups on a given solute molecule seems to be much greater in water than in any of the other solvents studied, making it more difficult to identify group contributions to solvation in water. Another example of the complexity of the solvation of alkyl groups in water is encountered when one compares the solvation enthalpy of hexane in various solvents with some of the above results.

Hydrophobic interaction in water-ethanol mixtures

Abstract: The solubility, free energy, entropy, and enthalpy of solutions of methane and ethane were determined in various mixtures of water and ethanol. The hydrophobic interaction for the pair methane-methane was computed, in these mixtures, using an approximate expression derived previously. Also the entropy and the enthalpy associated with the hydrophobic interaction were evaluated from the experimental data. The main finding is the steep decrease in the strength of the hydrophobic interaction as the mixture becomes richer in alcohol. The variation of the corresponding entropy and enthalpy also shows an abrupt change at the composition ofxethanol≈0.2. Some interpretations of these findings in terms of structural changes in the solvent are discussed.

Structural Aspects of Aqueous Tetraalkylammonium Salt Solutions

Abstract: Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of “cosphere” overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.

Solvation Equilibria in Very Concentrated Electrolyte Solutions

Abstract: A stepwise hydration-equilibrium model for aqueous electrolytes is developed and shown to give a good quantitative account of osmotic coefficients of strong, highly soluble electrolytes up to concentrations of 20–30 m. The main parameters needed are two equilibrium constants describing the stepwise hydration and the number of hydration sites. Choice of ion-size parameter has only a minor effect.

Conformation and Hydration of Sugars and Related Compounds in Dilute Aqueous Solution

Abstract: The effect of hydroxyl substitution on the nature of the hydration of an alkane chain has been studied by calorimetric techniques. Static permittivities (e0) of a range of monosaccharides and related compounds in aqueous solution have also been determined. The e0 data, suitably processed, have provided information about the solute dipole moments. In conjunction with earlier results from volumetric, compressibility, and relaxation studies, the specific hydration model is further developed and the relationships between solute molecular conformations and solute—water interactions are discussed.

Enthalpies of dilution of electrolyte solutions by flow microcalorimetry

Abstract: 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 φL 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.

A View of Electrolyte Solutions

Abstract: The uncertainties in the route to infinite dilution for 2–2 electrolytes are discussed in relation to the practical difficulties of determining the standard emf’s of simple reversible cells containing ZnSO4 in H2O and D2O solutions. These difficulties are due to uncertainties in the theory of highly charged ions in aqueous solution. Recent developments in theories of electrolytes, especially those for which numerical results are available, are critically evaluated for their accuracy and adaptability to changes in the solute potential. Simple refinements to the model (i.e., the solute potential) are described, and the changes are interpreted, in terms of the molecular interactions between sets or pairs of ions in the pure solvent. Recent work on the effect of solvent granularity and other molecular properties of the solvent (e.g., dipole moment) on the solute potential is reviewed.

Raman Spectra from Partially Deuterated Water and Ice VI to 10.1 kbar at 28°C

Abstract: High-pressure argon-ion laser-Raman spectra (4880 A excitation) have been obtained from partially deuterated water and ice VI (20 volume % D2O) in the OD and OH stretching regions to pressures of 10.1 kbar at 28°C. The Raman spectra from ice VI are the first to be reported at room temperature, and they are similar to the liquid spectra obtained at 9.7 kbar. Raman shifts corresponding to contour intensity maxima were observed to change with pressure rise in the OD and OH stretching regions from \( \Delta \bar v = 2513 - 2490\,{\text{cm}}^{ - 1} \) and \( \Delta \bar v = 3402 - 3380\,{\text{cm}}^{ - 1} \) respectively, for pressures from 1 bar to 10.1 kbar (ice VI). In addition, a shoulder observed at 1 bar on the OD contour near \( \Delta \bar v = 2650\,{\text{cm}}^{ - 1} \) became less distinct and was visually absent for pressures from 6.4 to 10.1 kbar, although a shoulder on the OH contour at about \( \Delta \bar v = 3250\,{\text{cm}}^{ - 1} \) intensified gradually for pressures to 9.7 kbar, and abruptly upon freezing at 10.1 kbar. The small effects of pressure on the OD component percentages obtained from computer analysis indicate that hydrogen-bond breakage is not a significant effect of pressure rise, and a downward change in the position of the OD stretching component having the largest Raman shift indicates that the nonhydrogen-bonded OD units or broken O-D…O bonds that exist at 1 bar are probably transformed by close packing due to compression into weak O-D…O bonds that are angularly deformed. In addition, intensification of the OH component at \( \Delta \bar v = 3220\,{\text{cm}}^{ - 1} \) upon freezing or upon pressurizing the liquid to 9.7 kbar is indicated by the computer analyses, and an increase in intermolecular coupling is thus favored, as opposed to enhancement of Fermi resonance, because the positions of components at \( \Delta \bar v = 3220\,{\text{cm}}^{ - 1} \) and \( \Delta \bar v = 3405\,{\text{cm}}^{ - 1} \) are nearly independent of pressure. The computer results also strengthen previous evidence indicating that the OD component which occurs at about \( \Delta \bar v = 2654\,{\text{cm}}^{ - 1} \) at 1 bar arises from broken O-D…O bonds, when it is understood that the severely deformed O-D…O bonds of ice VI give rise to intensity at a Raman shift of \( \Delta \bar v = 2617\,{\text{cm}}^{ - 1} \) , a difference of 37 cm-1 in the direction of stronger hydrogen-bonding.

The Role of Solvent Structure in Ligand Substitution and Solvent Exchange at Some Divalent Transition-Metal Cations

Abstract: The role of the solvent in reactions involving ions is considered in relation to the structure of liquids. The rate constants and activation parameters for ligand substitutions at divalent transition metal cations in various solvents are compared with those for solvent exchanges. The differences are related to structural properties of the solvents, represented by their heats of evaporation and fluidities, and interpreted with the aid of a model developed from that of Frank and Wen. Water is not a typical solvent.

Toward a Model for Liquid Water

Abstract: A new model is proposed for liquid water. It is obtained by consideration of the two transitions (melting and boiling) which define the liquid phase. These transitions are discussed with the aid of two analogies to well-known phenomena in polymer physical chemistry. In analogy to the helix-coil transition in polypeptides and polynucleotides, the melting of ice is viewed as a process consisting essentially of the destruction of the orderly interconnected small rings of hydrogen bonds characteristic of the crystal. The fact that the breakup of interconnected small rings is cooperative, even when unaccompanied by the breaking of bonds which are not parts of rings, is clearly seen by inspection of the theory for the putatively analogous helix-coil transition. The condensation of water vapor is viewed in analogy to gelation in reversibly polymerizing systems, an analogy which interprets its cooperativity. Taken together, these interpretations of the phase transitions indicate that the liquid can be viewed as an infinitely and randomly branched “gel” of (rapidly interchanging) hydrogen bonds in which closures of rings (primarily large rings) are present at random but in which there is no significant preference for an ordered array of small rings. These concepts also lead naturally to an interpretation of the triple point and sublimation. The random gel model is seen to be consistent with most of the known properties of liquid water. In particular, the radial distribution function, infrared and Raman spectra, dielectric properties, density maximum, and properties of the supercooled region are discussed briefly here.

Seawater—A test of multicomponent electrolyte solution theories. I. The apparent equivalent volume, expansibility, and compressibility of artificial seawater

Abstract: The apparent equivalent volume ΦV, expansibility ΦE, and compressibility ΦK of an artificial seawater solution containing10 ionic components (Na+, Mg2+, Ca2+, K+, Sr2+, Cl−, SO 4 2− , HCO 3 − , Br−, and F−) and one nonionic component (H3BO3) has been determined from0 to40°C (in5° intervals) and from0.1 to0.8 m ionic strength at1 atm. The concentration dependence (Iv=volume ionic strength) of the ΦV's, ΦE's, and ΦK's have been examined by using a Masson-type equation, Φ = Φ° +S'I V 1/2, and a Redlich-type equation, Φ = Φ° +SI V 1/2 +BI V, where Φ° is the infinite-dilution value, S′ is the empirical Masson slope, S is the theoretical Debye-Huckel slope, and B is an empirical deviation constant. By using Young's rule, Φ = ∑Eiφ(i), the apparent equivalent volumes, expansibilities, and compressibilities for “sea salt” have been estimated from the ionic and nonionic components making up the mixture. The estimated apparent molal quantities agree very well with the directly measured values providing the concentration terms, S i ′ and Bi, are weighted according to the methods of Wood and Reilly.

Concentrated Electrolyte Solutions at High Temperatures and Pressures

Abstract: A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe−H2O and CO2−H2O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.

Ionic Association in Hydrogen-Bonding Solvents!

Abstract: Studies on ionic association in hydrogen-bonding solvents including water, aliphatic alcohols, fluorinated alcohols, formamide, ethylene glycol, and propanol-acetone mixtures are compared. Data were derived from measurements of conductivity, ultrasonic absorption, and viscosity of electrolyte solutions and diffusion of nonelectrolytes. It is concluded that electrolyte solvents can be divided into three categories according to whether they solvate effectively cations only, anions only, or both cations and anions. Water and most other hydrogenbonding solvents constitute the third class, a group in which patterns of ionic aggregation are very similar. Fluorinated alcohols belong to the second class, showing significantly different ion-pairing behavior.

Models having the thermodynamic properties of aqueous alkaline earth halides and NaCl-MgCl2 mixtures

Abstract: A model studied earlier in relation to aqueous 1–1 electrolytes has been applied to the interpretation of the excess free energies of aqueous solutions of the alkaline earth halides up to 1 M ionic strength. Several variations on the model could be fitted to the data. In the one which seems most consistent with the other observations, the cospheres (hydration layers) on the M++ ions were two water molecules thick rather than one as for the alkali metal, tetraalkylammonium, and halide ions. The overlap of cospheres of an M++, M++ pair was found to make a small attractive contribution to the interionic force, while the overlap of cospheres of an M++, X− pair makes a small positive contribution which is almost the same for X−=Cl−, Br−, or I−. Thus, ionic hydration shells which are not penetrated by other ions are not required to account for the observed excess free energies. The model is also fitted to NaCl-MgCl2 mixtures to see whether the new cosphereoverlap parameter which must be determined is consistent with the others. The calculation also shows how the thermodynamic behavior of the mixtures is consistent with the mixture limiting law for unsymmetrical mixtures. The singularities in the mixing coefficients g0 and w0 at infinite dilution dominate their concentration dependence only up to ionic strengths of about 0.01 M in models which fit the data.

Glass-forming composition regions and glass transition temperature in nonaqueous electrolyte solutions

Abstract: With an interest in assessing the suitability of various nonaqueous solutions for electrolyte studies in the viscous region of the liquid state, the glass-forming properties of solutions of calcium nitrate dissolved in various nonaqueous solvents have been determined and compared with the corresponding aqueous solution properties. Solutions in dimethyl formamide prove of particular interest. The composition dependence of the glass temperature is similar in all solvents at high salt contents. “Ideal” glass temperatures, estimated from thermodynamic data for the pure solvents, are compared with experimental or extrapolated values.

The CO2-water system. I. Study of the slower hydration-dehydration step

Abstract: Using pressure-jump, concentration-jump, and stopped-flow methods, we have studied the rate of dehydration (k−1) of carbonic acid as a function of temperature (0–40°C) and ionic strength (0.005–3M NaCl, 3M LiBr) in both H2O and D2O. A new design of pressure-jump cell with reliable temperature control, as well as improved sensitivity in the spectrophotometric detection for stopped flow, enabled k−1 values to be determined with an accuracy better than ±8%, based on a comparison of results obtained using five different techniques. The influence of ionic strength, temperature, and isotope effects are discussed.

Thermodynamics of bolaform electrolytes. I. Heat capacities and enthalpies in H2O and D2O

Abstract: The partial molal heats of solution at infinite dilution, ΔH s o , of bolaform salts [Et3N(CH2)nNEt3]Br2 and [allyl3N(CH2)nNallyl3]Br2, have been measured in H2O and D2O at 25°C using a solution calorimeter. The values of ΔH s o were endothermic for almost all of the compounds studied. Values of ΔH s o were obtained as a function of temperature for several homologs in H2O and D2O. Positive ΔC p o values obtained from least-squares analyses of the ΔH s o vs T data show an almost linear dependence on the number of methylene groups between the nitrogen centers. Whereas the enthalpy of transfer from H2O to D2O is small and endothermic, relatively large positive heat capacity of transfer data, increasing with increased hydrocarbon content of the salts, were observed. The ability of the bolaform cation to act as a model for cation-cation pairing in R4NX systems is discussed.

The conductance of lanthanide (III) sulfate solutions in D2O

Abstract: The formation constants of the LnSO4+ complexes are reported for La3+, Pr3+, Sm3+, Dy3+, Yb3+, and Lu3+ in D2O and for Sm3+ and Lu3+ in water at 25°C. Formation constants which were calculated from conductance data are identical with those obtained in H2O within the limits of the assumptions made in the mathematical analysis.

Ultrasonic absorption in aqueous salts of the lanthanides. IV. Sulfates in D2O

Abstract: The rates of formation of the monosulfate complexes of the trivalent rare earth ions of Pr, Sm, Gd, and Dy have been measured at 25°C in D2O and additional measurements made on Pr, Sm, Gd, Tb, and Ho in water. Using formation constants recently calculated from conductance measurements in D2O, the rate data were compared to our reevaluated data in water to establish if a solvent isotope effect was present, which may contribute to our understanding of the mechanism of complexation. Contrary to previous reports, none is observed, the rate constants being in agreement within experimental error and within the limits of the assumptions used in the mathematical interpretation. Evidence therefore points to a dissociative mechanism in which the rate of exchange of the solvent from the primary hydration sphere of the cation is rate-determining.

Isothermal diffusion studies of the H2O-sucrose-KCl system at 25°C

Abstract: Diffusion coefficients were obtained for two compositions of the system H2O-sucrose-KCl at 25°C. These plus published diffusion coefficients of the same system at two other compositions led to the construction of three-dimensional surface diagrams. Using these diagrams, the diffusion coefficients of the ternary system were compared with those of binary systems of components. The main diffusion coefficient of KCl was estimated from the conductivity data of KCl in aqueous solution of sucrose, and the agreement of these with experimental values was found to be satisfactory. The possible cause for the appreciable size of the cross-term diffusion coefficients is discussed.

Electric dipole moments in polar solvents. I. Audiofrequency measurement with slightly conducting solutions

Abstract: Audiofrequency methods were used to measure dielectric constants of dilute solutions containing electrolytes up to free-ion concentrations of 10−4M. Using a calibrated transformer bridge, capacitance was measured with an accuracy of 0.03 pF at a conductance of 100 μmho and within 0.3 pF at 800 μmho. Evaluation of the double-layer capacitance from the frequency dependence of the data is discribed. The effect of the free ions on the dielectric constant is found to be relatively large and in reasonable agreement with the prediction of the Debye-Falkenhagen theory. The calculation of the electric dipole moment for polar solutes, including ion pairs, is discussed in terms of Kirkwood's theory. Experimental tests are described for finding out whether possible deviations of Kirk-wood's correlation factors from unity may be neglected. These tests involve changing the solvent and the temperature. The tests were satisfied for the ion pairs of tetraisoamylammonium nitrate and for nitrobenzene in chlorobenzene and acetic acid.

A neutron inelastic scattering investigation of the diffusion kinetics of H2O molecules and hydration complexes in concentrated ionic solutions

Abstract: Intermolecular frequencies of H2O's and the diffusion kinetics have been investigated by neutron inelastic scattering for concentrated ionic solutions containing small and/or multiply charged cations (e.g., Cr+3, Mg+2, Ca+2, and Li+1). As higher concentrations are approached such that the majority of H2O's are in hydration layers, their exchange time can exceed the neutron interaction time. Then the diffusion kinetics depart functionally from activated reorientations of individual H2O's characteristic of lower concentrations and evolve to continuous diffusion processes of hydration complexes characterized by small self-diffusion coefficients. The general features of the observed evolution in the functionality of the diffusion kinetics are found to be functionally consistent with an approximate model which includes contributions from the delayed diffusional exchange of individual H2O's as well as the continuous diffusion of hydrated ions. At a given concentration, the temperature interval over which this evolution in functionality occurs increases both with increasing strength of the primary cation-H2O coordination and with anion basicity. Further, as the temperature decreases, frequencies of defined cation-water hydration complexes gradually sharpen in a continuous manner, showing no abrupt variations at glass transitions. Anions of increasing basicity decrease the self-diffusion coefficients of the ion-water complexes and perturbed frequencies characteristic of cation-water hydration complexes. Such anion effects, at high concentrations, correspond to an increasing degree of time-average indirect or direct ion pairing with increasing anion basicity. This results, in turn, both in a distortion or partial disruption of the cation hydration sheaths and in a degree of coupling and/or “bridging” between anions and hydrated cations so as to increase the effective masses and friction coefficients associated with their diffusional motions.

Enthalpy of dilution and heat capacity of aqueous solutions of tetrabutylammonium butyrate as a function of temperature

Abstract: Enthalpies of dilution of tetrabutylammonium butyrate are reported as a function of temperature between 10° and 50°C. Heat capacities of aqueous solutions of tetrabutylammonium butyrate were measured in order to obtain values ofφcp at 15°, 25°, and 35°C. These data were combined with the enthalpy of dilution data to obtain φcp as a function of molality and temperature. The apparent molal heat content φL decreased with increasing temperature in concentrated solutions but increased with increasing temperatures in dilute solutions (below0.7 m). Over the temperature range studied φcp shows a maximum as a function of molality at approximately 0.5m. The decrease in φcp with increasing concentration of hydrophobic solute is consistent with the view that the hydrophobic hydration cages, formed under the influence of the tetrabutylammonium and butyrate ions, are saturated at about 0.5m, and that at higher molalities increased overlap of the hydration cages occurs.

Nuclear magnetic relaxation and structure of aqueous solutions

Abstract: By the interpretation of the intermolecular nuclear magnetic relaxation rate of 19F the orientation of the water molecules in the hydration sphere of F− can be determined. Similarly, the orientation of the water molecules around the methyl group of propionic acid in aqueous solution has been studied. Experiments are described which give information about the nature of association of solute in aqueous solution of a number of carboxylic acids and of ethanol. The local dynamic details of the I− ion have been investigated. Some new results are briefly discussed regarding the nuclear magnetic relaxation by quadrupole interaction in electrolyte solutions.

Transference numbers for anhydrous methanol solutions at 10 and 25°C

Abstract: Transference numbers are reported for LiCl and NaCl in methanol at 25°C and for NaCl, KCl, and Bu4NBr in methanol at 10°C. The potentiometric moving-boundary method as developed by Kay and Fratiello was employed to give a precision of about 0.05% and an accuracy of at least 0.1% as indicated by two independent determinations of the conductances of the Cl− and Br− ions. The data are extrapolated by the Fuoss-Onsager theory, and the magnitude of the electrophoretic effect is calculated as described by Kay and Dye. The agreement with this theory is quite good at both temperatures, although the a value required in the case of Bu4NBr is considerably larger than that obtained from conductance data. This agreement contrasts with that obtained for ethanol and acetone solutions where the measured electrophoretic effect is considerably larger than the corresponding calculated values. The importance of this fact in the determination of ion-pair association constants is discussed.

Heats of transport of some chlorides in H2O and D2O

Abstract: Heats of transport of 0.01 m HCl, Me4NCl, and Et4NCl in H2O and 0.01 m KCl, NaCl, and CsCl in D2O were determined from the measurement of initial (homogeneous) and final (Soret steady state) thermoelectric powers of the thermocell (T)Ag−AgCl/Solution/AgCl−Ag(T+ΔT) at a mean temperature of 25°C. The results are discussed in terms of ion-solvent interaction and properties of H2O and D2O.

Dissociation constant of protonated tris(hydroxymethyl)aminomethane in N-methylpropionamide and related thermodynamic quantities from 10 to 55°C

Abstract: The dissociation constant of protonated tris(hydroxymethyl)aminomethane (tris·H+) in the solvent N-methylpropionamide (NMP) has been determined at intervals of 5°C from 10 to 55°C by measurement of the emf of cells without liquid junction using hydrogen and silver-silver chloride electrodes. At 25°C, pK a was found to be 8.831, as compared with 8.075 in water. The standard changes in Gibbs energy, enthalpy, and entropy for the dissociation process have been evaluated from the dissociation constant and its change with temperature. By comparison with similar data for the dissociation of tris·H+ in water, thermodynamic functions for the transfer from water to NMP have been derived. The dissociation process is isoelectric, and the solvent dielectric constant is high (e=176 at 25°C). Consequently, electrostatic charging effects are expected to be minimal, and the change in dissociation constant depends primarily on solute-solvent interactions. The results, combined with transfer energies for HCl, tris, and tris·HCl from emf and solubility measurements, demonstrate that the decreased acidic strength of tri·H+ in NMP is attributable in large part to the fact that NMP is less effective than water in stabilizing tris and its salts.

Electric dipole moments in polar solvents. II. Tetraisoamylammonium nitrate ion pairs in chlorobenzene. Effect of mutual polarization of the ions

Abstract: The dielectric constant and conductivity of dilute solutions of tetraisoamylammonium nitrate in chlorobenzene are measured between −34.6° and 99.0°C to give association constants for the formation of ion pairs (K A) and triple ions, and electric dipole moments. The quantityK A as a function of temperature is reproduced by the Denison-Ramsey-Fuoss treatment for unolarized ion pairs [Eq. (2)] with a distance of closest approach of 4.90 A. The dielectric data are reproduced by Onsager's equation with an inherent (gas-phase) dipole moment of the ion pairs of 14.2±0.3 D. Other methods of calculation lead to consistent dipole moments, confirming that the mutual polarization of the ions is important. The energetics of ionic association is considered on the basis that the ion pair may be treated as a polarizable dipole in a spherical cavity.