Rj. Prankerd et Mz. Elsabee, THERMAL-ANALYSIS OF CHIRAL DRUG MIXTURES - THE DSC BEHAVIOR OF MIXTURES OF EPHEDRINE HCL AND PSEUDOEPHEDRINE HCL ENANTIOMERS, Thermochimica acta, 248, 1995, pp. 147-160
A method for peak shape analysis and deconvolution of overlapping endo
therms in differential scanning calorimetry (DSC) data has been previo
usly reported. In this study the method is applied to binary mixtures
of, (i) (1S,2S)-(+)- and (1R,2R)-(-)-PSI-ephedrine HCl, and (ii) (1S,2
S)-(+)-PSI-ephedrine HCl and its diastereomer, (1S,2R)-(+)-ephedrine H
Cl. Phase diagrams based on enthalpies of fusion at the melting point
(DELTAH(f)m) as a function of mol% composition are linear. However, th
e phase diagrams based on melting temperature as a function of mol% co
mposition are non-linear and show deviations from the theoretical Prig
ogine-Defay and Schroder-van Laar equations. Estimates of eutectic com
positions are more definitive from the diagrams based on DELTAH(f)m va
lues. The phase diagram for the PSI-ephedrine HCl enantiomers demonstr
ates racemic compound formation with eutectic points for the compound
and the pure enantiomers at 28.1 +/- 2.5 mol% and 71.9 +/- 2.5 mol%. T
he DELTAH(f)m phase diagram for mixtures of (1S,2R)-(+)-ephedrine HCl
and (1S,2S)-(+)-PSI-ephedrine HCl suggested the formation of a weak co
mplex with a composition close to 60 mol% of the (1S,2S)-(+)-isomer.