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 hydrogen-bonded solutions: development of a predictive equation for the solubility of anthracene in binary hydrocarbon
Abstract Acree W.E., Jr., Zvaigzne A.I. and Tucker S.A., 1994. Thermochemical investigations of hydrogen-bonded solutions: development of a predictive equation for the solubility of anthracene in binary hydrocarbon + alcohol mixtures based upon Mobile Order theory. Fluid Phase Equilibria, 92: 233-253. Experimental solubilities are reported for anthracene dissolved in twelve binary solvent mixtures containing either 2-propanol or 1-octanol with n -hexane, n -heptane, n -octane, cyclohexane, methylcyclohexane and 2,2,4-trimethylpentane at 25.0°C. Results of these measurements, along with previously published solubility data for anthracene in binary 1-propanol+alkane and 1-butanol + alkane mixtures, are used to test the limitations and applications of expressions derived from Mobile Order theory. The best descriptive equation expresses the logarithm of the volume fraction solubility in binary mixtures as a simple volume fraction average of the corresponding logarithm solubilities in the two pure solvents, and contains additional terms to represent contributions from nonspecific physical interactions between dissimilar solvent components, from molecular size disparity, and from the reduction in mobile disorder caused by the self-association by hydrogen bonding of the alcohol solvent. The newly derived expression predicts the observed anthracene solubilities to within an overall average deviation of ca. 4.4% using a single value of K c = 5000 for the self-association equilibrium constant.
Determination of iodide with 1,3-dibromo-5,5-dimethylhydantoin (DBH) in comparison with the ICl-method. Analytical methods of pharmacopeias with DBH in respect to environmental and economical concern. Part 3.
USP 1995 (The United States Pharmacopeia, 23rd Edit., (1995), potassium iodide p. 1265, sodium iodide p. 1424), PH. EUR. 1997 (European Pharmacopoeia, third ed., Council of Europe, Strasbourg, (1997), potassium iodide p. 1367, sodium iodide p. 1493) and JAP 1996 (The Japanes Pharmacopoeia, 13th ed. (1996), potassium iodide p. 578, sodium iodide p. 630) determine iodide with the ICl-method (J. Am. Chem. Soc. 25 (1903) 756-761; Z. Anorg. Chem. 36 (1903) 76-83; Fresenius Z. Anal. Chem. 106 (1936) 12-23; Arzneibuch-Kommentar, Wissenschaftliche Erläuterungen zum Europäischen Arzneibuch, Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, Govi-Verlag - Pharmazeutischer Verlag GmbH, Eschborn, 12th suppl. (1999), K10 p. 2), using chloroform, which is toxic and hazardous to environment. Without the application of chlorinated hydrocarbons USP 2000 (The United State Pharmacopeia, 24th ed. (2000), potassium iodide p. 1368, sodium iodide p. 1535) and Brit 1999 (British Pharmacopoeia London, (1999), Appendix VIII C, p. A162) titrate iodide with the redox indicator amaranth. A titration with potentiometric indication giving two end-points at the step of I(2) and [ICl(2)](-) is described. Due to the high concentration of hydrochloric acid required for the ICl-method, the determination with DBH (1,3-dibromo-5,5-dimethylhydantoin; 1,3-dibromo-5,5-dimethyl-2,4-imidazolidinedione) can be recommended and is performed easily. Similarly, the iodide content of gallamine triethiodide may be analyzed with DBH by application of a visual two-phase titration in water and ethyl acetate or with potentiometric indication in a mixture of 2-propanol and water. During the removal of the excess of DBH 4-bromo-triethylgallamine (2,2',2"-[1-bromo-benzene-2,3,4-triyltris(oxy)]N,N,N-triethylethanium) is formed.