Calorimetric determination of the heat of precipitation of pseudoephedrine racemic compound--its agreement with the heat of solution.
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.
Pudipeddi
M
M
School of Pharmacy, University of Wisconsin, Madison 53706, USA.
Sokoloski
T D
TD
Duddu
S P
SP
Carstensen
J T
JT
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
D012996:Solutions; D004809:Ephedrine