Organic Nonelectrolytes Research Articles

Vaporization enthalpy of azeotropes by the solution calorimetry method

This work is devoted to the study of the thermochemistry of solvation of azeotropes. The enthalpies of dissolution of azeotropes (binary systems [organic nonelectrolyte – A], where A is acetonitrile, benzene, cyclohexane or n-hexane) in the medium of cyclohexane or n-heptane have been determined. The impact of the structure of the components of the azeotropes on their properties in solution has been discussed. The approach based on the correlations between the enthalpies of solvation and molar refraction has been first used to determine the vaporization enthalpies of azeotropes. Values were found to be in a fairly good agreement with literature data obtained by direct and calculated methods. The findings of this study allow analyzing the structure–property relationships of the azeotropes obtained.

Compensation relationship in thermodynamics of vaporization of aromatic and aliphatic compounds and their heat capacities

It is long known that there is a correlation between the Gibbs energies and enthalpies of many processes, particularly solvation and vaporization, which is called the compensation relationship. Recently, we established that the correlation between the Gibbs energies and enthalpies of vaporization of non-hydrogen-bonded organic non-electrolytes at 298.15 K is divided into the two linear relationships with different slopes in the cases of aromatic and long-chain aliphatic compounds. We also recently found that there is a correlation between the difference between the heat capacities of the liquid and ideal gas, on the one hand, and the vaporization enthalpy at 298.15 K. Similarly with the compensation relationship, it is different in the cases of aromatic and aliphatic compounds.In this work, our goal was to establish the factors defining the values of the coefficients of the Gibbs energy-enthalpy correlation and understand its features in aromatic and aliphatic compounds. The thermodynamic analysis enabled to independently determine the coefficients of the compensation relationship, investigate their possible boundaries, and explicitly show how they depend on the difference between the heat capacities of the liquid and ideal gas and boiling entropy. Slight variations in the boiling entropy of non-hydrogen-bonded compounds appeared to have almost no effect on the compensation relationship, while the difference in the slopes exhibited by aromatic and aliphatic molecules was due to the features of the heat capacity-enthalpy dependence.

Compensation relationship in thermodynamics of solvation and vaporization: Features and applications. II. Hydrogen-bonded systems

There is a well-known extrathermodynamic correlation between the entropies (or Gibbs energies) and enthalpies of many processes, including solvation and vaporization, called the compensation relationship. Non-hydrogen-bonded species, from rare gases to organic non-electrolytes, follow a common correlation between the Gibbs energies and enthalpies of solvation in solvents incapable of self-association. The Gibbs energies of solvation of apolar molecules in hydrogen-bonded solvents and ionic liquids tend to deviate towards the higher values on the compensation plot, which is known to be a manifestation of the solvophobic effect.However, there are more options for hydrogen bonding upon solvation, whose effect on the compensation relationship has not yet been studied, either qualitatively or quantitatively. In this work we classified hydrogen-bonded solute–solvent systems into the three types and quantitatively investigated the deviations arising in each case: 1) apolar solutes solvated in hydrogen-bonded solvents (e.g., octane in water); 2) solutes capable of hydrogen bonding with non-self-associated solvents (chloroform in pyridine); 3) solutes capable of hydrogen bonding with hydrogen-bonded solvents (chloroform in ethanol).Furthermore, we have shown how to predict the solvation enthalpies in various hydrogen-bonded systems, knowing the Gibbs energies of solvation and the molecular structures of the solute and solvent. The agreement between the predicted and literature values (RMS < 1.5 kJ·mol−1, N = 211) confirmed the regularities observed in each case.

Application of Solution Calorimetry to Determining the Fusion Enthalpy of an Arylaliphatic Compound at 298.15 K: n-Octadecanophenone

Evaluating the temperature dependence of the fusion enthalpy is no trivial task, as any compound melts at a unique temperature. At the same time, knowledge of the fusion enthalpies under some common conditions, particularly at the reference temperature of 298.15 K, would substantially facilitate the comparative analysis and development of the predictive schemes. In this work, we continue our investigations of the temperature dependence of the fusion enthalpy of organic non-electrolytes using solution calorimetry. As an object of study, n-octadecanophenone, an arylaliphatic compound was chosen. The solvent appropriate for evaluating the fusion enthalpy at 298.15 K from the solution enthalpy of crystal was selected: p-xylene. The heat capacity and fusion enthalpy at the melting temperature were measured by differential scanning calorimetry to derive the fusion enthalpy at 298.15 K from the Kirchhoff’s law of Thermochemistry. An agreement between the independently determined values was demonstrated. This particular result opens a perspective for further studies of the fusion thermochemistry of arylaliphatic compounds at 298.15 K by solution calorimetry.

Compensation relationship in thermodynamics of solvation and vaporization: Features and applications. I. Non-hydrogen-bonded systems

There is a well-known connection between the entropies (or Gibbs energies) and enthalpies of many processes, particularly solvation, called the compensation relationship. It has been recognized for a long time that hydrogen bonding in solvents has a significant effect on the compensation relationship. However, apart from that, little attention has been paid to the features of the correlation between the Gibbs energies and enthalpies of solvation that may manifest different classes of organic non-electrolytes.In this work we examined whether the Gibbs energies and enthalpies of solvation and vaporization of various non-hydrogen-bonded organic non-electrolytes obeyed the same relationship. It was established that, while most organic non-electrolytes, together with rare gases, follow the common linear correlation, long-chain aliphatics form the separate line with the lower slope.Root-mean-square deviation of the observed correlations was below 1 kJ·mol−1, which enables to use them as a tool for predicting the Gibbs energies of solvation/vaporization from the enthalpies at 298.15 K and vice versa. Combined with our recent findings, this can be applied to determining the vapor pressure as a function of temperature from the vaporization enthalpy, or a single measurement of the vapor pressure at an arbitrary temperature, or the boiling point under a given pressure.

Comparison of isochoric and isobaric heat capacities of liquid organic non-electrolytes and their vaporization enthalpies

The present paper is devoted to the study of the relationship between the difference of isochoric heat capacities of liquid and ideal gas phase organic non-electrolytes and their vaporization enthalpy at 298.15 K. This investigation is intended to more deeply analyze the origin of the recent finding that the difference of isobaric heat capacities of organic compounds in liquid and ideal gas phase is in a linear correlation with the vaporization enthalpy. We showed that the difference of isobaric and isochoric heat capacities of liquid aromatic compounds is constant within 3 J·K−1·mol−1 and does not depend on the vaporization enthalpy. A direct proportionality between isochoric heat capacity change and the vaporization enthalpy was established for 84 compounds, which included not only aromatic liquids but other rigid and relatively inflexible molecules (root-mean-square deviation equaled 2.5 J·K−1·mol−1). The slope agreed with that of isobaric heat capacity change – vaporization enthalpy correlation. Statistical significance of the established relationship far exceeded correlations with other molecular size-related parameters, namely the heat capacities, molar volume, and molecular weight.

Controlling the thermal response of poly(N-isopropylacrylamide)-poly(ethylene glycol)- poly(N-isopropylacrylamide) triblock copolymers in aqueous solution by means of additives

The present work describes how the thermal response of some thermosensitive poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) triblock copolymers of different compositions, in aqueous solution, estimated by the cloud point (CP) method, can be controlled by factors like polymer concentration (0.05–5 wt%) and composition (PNIPAM and PEG blocks length, overall polymer hydrophilicity), as well as by the nature and concentration (0.1–0.4 M) of some water-soluble additives. The experiments showed that CP decreased with polymer concentration and molecular weight (MW) of the PNIPAM block and increased with the MW of the PEG block. The influence of inorganic and organic salts through both their anion and cation, and short-alkyl chain organic nonelectrolytes through their alkyl chain architecture (linear or branched) and polarity of the functional group (alcohol, aldehyde, amine, carboxyl) was also investigated. Neither the composition nor the hydrophilicity of our triblock copolymers displayed any appreciable influence upon CP increase/decrease in the presence of additives. It was proved by hysteresis loop area measurements that NaCl addition increased the hysteresis effect of the polymer soluble - insoluble reversible transition.

Extraction of organic non-electrolytes with n-hexane from aqueous solutions of dipotassium phosphate and potassium acetate

At a temperature of 20 ± 1 °C, the distribution of model substances of various classes of organic non-electrolytes in n-hexane – aqueous solutions of dipotassium phosphate and potassium acetate was studied. The increments of the methylene and functional groups of organic non-electrolytes are calculated. It has been shown that in case of dipotassium phosphate, the nature of the salting out effect is enhancing the structure of the salt solution and the growth of the methylene group increment. For potassium acetate, the increment of the methylene group slightly increases with increasing salt concentration, and for most functional groups it increases significantly. An explanation of the dependences of the increment values on the nature and composition of the salt solution is given.

New aspects in the thermochemistry of solid-liquid phase transitions of organic non-electrolytes

Thermochemistry of solid-liquid phase transitions plays an important role in solidification studies of polymers, metals, inorganic salts, and low-molecular organic compounds. Enthalpy of fusion is a source of information about intermolecular interactions in materials, crystallinity, mixtures phase diagrams shape, heat transfer in the solidification interval.The present paper is devoted to relationship between the fusion enthalpies of aromatic compounds at the melting temperature and the solution enthalpies in benzene at 298.15K. Sublimation and vaporization thermochemistry are used as an additional source of information about the latter relationship. Depending on the magnitude of deviation between the solution enthalpies in benzene at 298.15K and fusion enthalpies at the melting temperature, aromatic compounds are conventionally divided into three groups. For a large number of aromatic compounds not capable of self-association the equality between the fusion enthalpies at the melting temperature and the solution enthalpies in benzene at 298.15K is established. For self-associated aromatic compounds the solution enthalpy in benzene at 298.15K exceeds the fusion enthalpy at the melting temperature, and insertion of a substituent not forming inter- and intramolecular hydrogen bonds does not affect the difference between the solution and fusion enthalpies. The enthalpies of solution in benzene at 298.15K of several aromatic compounds not capable of self-association appear to be visibly less than the fusion enthalpies at the melting temperature. The reasons of different relationships between the fusion and solution enthalpies are analyzed using Kirchhoff's law for the fusion enthalpy.

Predicting the Octanol Solubility of Organic Compounds

The molar octanol solubility of an organic nonelectrolytes can be reasonably predicted solely from its melting point provided that its liquid (or a hypothetical super-cooled liquid) form is miscible with octanol. The aim of this work is to develop criteria to determine if the real or hypothetical liquid form of a given compound will be miscible with octanol based on its molar volume and solubility parameter. Fortunately, most organic compounds (including most drugs) conform to the criteria for complete liquid miscibility, and therefore have solubilities that are proportional to their melting points. The results show that more than 95% of the octanol solubilities studied are predicted with an error of less than 1 logarithmic unit.

Solubilities of selected organic electronic materials in pressurized hot water and estimations of aqueous solubilities at 298.15 K

Increasing production and disposal of organic light-emitting diode (OLED) displays for smartphones and tablets may have impact on the environment depending on the aqueous solubility of the pertinent chemicals. Here, aqueous solubilities are presented for several compounds, mostly aromatic amines, used as hole transport materials in the OLED displays. Solute selection includes 1,4-bis(diphenylamino)benzene, tetra-N-phenylbenzidine, 4,4′-bis(N-carbazolyl)-1,1′-biphenyl, 1,3,5-tris(diphenylamino)benzene, and 9,10-bis(phenylethynyl)anthracene. The solubilities are those in pressurized hot water (PHW), i.e., measured at elevated temperature (up to 260°C) and pressure. The semi-quantitative estimates of room-temperature solubilities of the solutes have been obtained from extrapolations of the solubilities in PHW. For the compounds studied, the estimated aqueous solubilities at room temperature do not exceed 2×10−11g of the solute per 1kg of water. Aqueous solubilities of triphenylamine have also been measured and used to upgrade a recent group-contribution model of aqueous solubilities of organic nonelectrolytes with the parameters for the nitrogen atom in aromatic amines.

Distribution constants of lower alcohols, acetone, and ethyl acetate in n-hexane-aqueous solutions of inorganic salt systems and the nature of the salting-out effect

The distribution of model oxygen-containing organic nonelectrolytes in n-hexane-aqueous solutions of mineral salts (KF, (NH4)2SO4, K2CO3, K3PO4) and lower alcohol-saturated aqueous solutions of salt (KF, K2CO3, K3PO4) systems are studied at a temperature of 20 ± 1°C. Increments of the methylene and functional groups of organic nonelectrolyte of partition constants logarithm are calculated. It is shown that the nature of the salting-out effect primarily involves strengthening of the salt solution’s structure and growth of the methylene group increment. A comparative characteristic of various salts according to the degree of their structuring effect and the effectiveness of the salting-out of organic nonelectrolytes from aqueous solutions is given.

Distribution of Organic Solutes in Biphasic 1-n-Butyl-3-methylimidazolium Methyl Sulfate−Supercritical CO2 System

Interphase distribution of organic nonelectrolytes can be important in applications of biphasic solvent systems composed of a room-temperature ionic liquid and supercritical carbon dioxide (scCO(2)). Here, open tubular capillary-column supercritical fluid chromatography (SFC) with 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][MeSO(4)]) as the stationary liquid and scCO(2) as the carrier fluid was employed to measure retention factors of organic solutes within 313-353 K and 8.5-23.2 MPa. Solute selection included 18 compounds of diverse volatilities and chemical functionalities. The retention factors were converted to infinite-dilution solute partition coefficients in the biphasic [bmim][MeSO(4)]-scCO(2) system. At a constant temperature, an increase in scCO(2) density produced distinct shifts in relative retention (= separation factor), thus providing some pressure-tunable selectivity. At a particular temperature and density of CO(2), solute partition coefficients can be correlated in terms of linear solvation energy relationships. Analysis of the relative retention data by regular solution theory resulted in approximate values of the solubility parameter of CO(2)-expanded [bmim][MeSO(4)].

ChemInform Abstract: Solution Calorimetry of Organic Nonelectrolytes as a Tool for Investigation of Intermolecular Interactions

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Solution calorimetry of organic nonelectrolytes as a tool for investigation of intermolecular interactions

AbstractThe paper is mainly the review and generalization of the previous publications of the authors. It demonstrates that solution calorimetry method gives the opportunities of more detailed understanding of various aspects of intermolecular interactions in solution. We are assured that prerequisite to such an understanding is the successive analysis of various solute–solvent systems from the simplest ones which include alkanes as a solute or as a solvent to the most complex systems with solvent self‐association via hydrogen bonding. Particular findings discussed in this paper are (i) an inconspicuous contribution of electrostatic solute–solvent interaction to the solvation enthalpy and, accordingly, the dominating contribution of dispersion interactions for nonspecifically solvated solutes; (ii) new, very general method for the extraction of specific interaction enthalpy from the enthalpy of solvation; (iii) new method of determination of self‐association enthalpies for the solvents associated via hydrogen bonding; (iv) new method for determination of cooperative hydrogen bonding enthalpies of proton acceptors with associated species of alcohols; (v) the unique method of experimental determination of the hydrophobic effect enthalpy. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Interrelation between thermodynamic similarity numbers and topological characteristics of the structure of organic molecules

The concept of the existence of nonpolar and low-polarity aprotic organic nonelectrolytes predominantly in the state of rotational motion in the liquid phase was used to show that the thermodynamic similarity numbers of several normal alkanes were interrelated with their molecular weights multiplied by the Wiener topological index raised to a power of 2/3.

Additivity of adiabatic compressibility with the size and geometry of the solute molecule

It was shown for dilute aqueous solutions of few homologous series of organic non-electrolytes that the effect of solutes on compressibility decrease is directly linked to the length of their molecules and the groups, which are their constituents. The contributions of the groups – constituents of solute molecules – have been determined and discussed. It seems possible now to predict compressibility of aqueous solutions of organic non-electrolytes only from their structural formulae.

Hydration numbers of non-electrolytes – Application of the acoustic method of Pasynski

Applicability of the acoustic Pasynski method of determination of hydration numbers for non-electrolytic aqueous solutions has been tested and discussed. It was shown for dilute aqueous solutions of few homologous series of organic non-electrolytes that the hydration numbers are strongly and directly depending on the length of solute molecules and the groups which are their constituents. Thus, the results suggest that hydration is an additive parameter, although its mechanisms are different.

Characterization of the diffusion of non-electrolytes across plant cuticles: properties of the lipophilic pathway

Systemic crop protection products are commonly sprayed onto foliage, whereupon the active substances must penetrate into the leaves in order to become biologically active. Penetration of the plant cuticle is the rate-limiting step. The diffusion of organic non-electrolytes within cuticles is a purely physical process that can be described and analysed in the same way as is done for diffusion in synthetic polymer membranes. Solute mobilities in cuticles vary considerably between plant species. For a given species they decrease with increasing solute size, and this size selectivity holds for all of the plant species investigated so far. Wax extraction from leaf cuticles increases the mobility of solutes tremendously, but size selectivity is not affected. Furthermore, diffusion within plant cuticles is extremely temperature dependent. An analogous increase in solute mobility can be achieved by using accelerators, which enhance the fluidity of the polymer matrix and of the waxes. The effects of temperature and plasticizers on the diffusion of non-electrolytes in wax and the cutin matrix have been used to characterize the nature of the lipophilic pathway. The 'free volume' theory can be used to explain the influence of the size and shape of the solute, and its dependence on temperature. The physico-chemical nature of the diffusion pathway has been shown, by thermodynamic analysis, to be identical for a wide range of solute lipophilicities. This approach also explains the mode of action and the intrinsic activity of plasticizers.

Estimation of the aqueous solubility of weak electrolytes

Jain and Yalkowsky [Jain, N., Yalkowsky, S.H., 2001. Estimation of the aqueous solubility. I. Application to organic non-electrolytes. J. Pharm. Sci. 90, 234–252.] demonstrated that the general solubility equation (GSE) can be used to estimate the aqueous solubility of organic non-electrolytes. In this study the applicability of the GSE was extended to weak electrolytes. It is demonstrated that the GSE estimates the aqueous solubility of 949 compounds, including 367 weak electrolytes with an AAE of 0.58. It is also shown that the intrinsic solubilities of weak acids for which the p K a + log S w ≤ 0 and for weak bases for which p K a − log S w ≤ 14 are within a factor of 2 of the total solubilities.