Thermochemical investigations of associated solutions: calculation of solute--solvent equilibrium constants from solubility measurements.
A simple solution model that has lead to successful predictive equations for the partial molar excess properties of a solute in simple binary solvent mixtures containing only nonspecific interactions is extended to include association between the solute and one of the solvent components. An expression is derived and tested for its ability to describe anthracene solubilities in binary solvent mixtures containing benzene. The best description of the experimental solubilities requires the formation of a 1:1 anthracene-benzene complex, with a molarity-based equilibrium constant of KcAC approximately equal to 0.107 M-1. In comparison, a stoichiometric complexation model which attributes all solubility enhancement to the formation of anthracene-benzene complexes requires a somewhat larger equilibrium constant (KcAC approximately equal to 0.228 M-1) to describe the solubility behavior of anthracene in the benzene-n-heptane system. The results of these calculations illustrate that the determination of solute-solvent equilibrium constants from solubility data depends on the theoretical model used and the manner in which nonspecific interactions are incorporated into the model.
Thermochemical investigations of associated solutions: 4. Calculation of carbazole-dibutyl ether association constants from measured solubility in binary solvent mixtures.
Experimental solubilities are reported for anthracene and carbazole in binary dibutyl ether plus n-hexadecane and dibutyl ether plus squalane solvent mixtures at 25 degrees C. Results of these measurements, used in conjunction with the extended nearly ideal binary solvent (NIBS) model, enabled calculation of the carbazole-dibutyl ether association constant. The numerical value obtained was independent of the hydrocarbon cosolvent, and compared favorably with previously reported values based on carbazole solubilities in solvent mixtures containing much smaller alkane cosolvents.
A STUDY ON THE THERMODYNAMIC PROPERTIES OF ASSOCIATED SOLUTIONS BY LINEAR ASSOCIATION MODELS
The excess thermodynamic properties of associated solutions are discussed by using the linear association models (I) and (II). The linear association model (I) deals with the self-associated system by making distinctions between the association constant and association energy of dimer formation and those of polymer formations. The results of the calculation show that the distinguishing effects are relatively small in quality. The linear association model (II) is proposed as one of the models for the system having the species associated with like and unlike molecules. A characteristic of this model is the existence of a maximum point on the activity coefficient curve. Good results are obtained in the application of model (II) to correlate and interpret the vapor-liquid equilibria for binary mixtures of alcohols and interacting solvents.