title: Calorimetric determination of the heat of precipitation of pseudoephedrine racemic compound--its agreement with the heat of solution.
abstract: The heat of precipitation of dl-pseudoephedrine was determined by direct calorimetry using a Tronac isoperibolic calorimeter. The precipitation of dl-pseudoephedrine was induced by mixing aqueous solutions of the two enantiomers, namely, d- and l-pseudoephedrine, directly in the calorimeter. The molar heat of precipitation of dl-pseudoephedrine was -2.7 and -3.0 kcal/mol at 25 and 30 degrees C, respectively. The aqueous solubility of dl-pseudoephedrine was determined over a temperature range of 20-40 degrees C. The van't Hoff solubility plot was nonlinear. The apparent heat of solution at saturation was obtained from the solubility data using a nonlinear regression model. A good agreement between the magnitude of the apparent heat of solution at saturation and the heat of precipitation was noticed at both 25 and 30 degrees C.
authors.affiliation: School of Pharmacy, University of Wisconsin, Madison 53706, USA.
authors.forename: M
authors.initials: M
authors.lastname: Pudipeddi
authors.forename: T D
authors.initials: TD
authors.lastname: Sokoloski
authors.forename: S P
authors.initials: SP
authors.lastname: Duddu
authors.forename: J T
authors.initials: JT
authors.lastname: Carstensen
mesh_terms: D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D011232:Chemical Precipitation; D002627:Chemistry, Physical; D004809:Ephedrine / Q000737:chemistry*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D012996:Solutions; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: D012996:Solutions; D004809:Ephedrine