Racemic Structures of Organic Ammonium Salts of N-Acetyl-DL-norleucine and Optical Resolution by Preferential Crystallization of the DL-Ammonium Salt
1986 Volume 1986 Issue 2 Pages 177-185
Details
1986 Volume 1986 Issue 2 Pages 177-185
The racemic structures of ammonium salt of N-acetyl-DL-norleucine and the DL-organic ammonium salts have been studied to explore the possibility of optical resolution by preferential crystallization. The DL-salts employed here were ammonium salt (DL-AM salt), methylammonium salt (DL-MA salt), ethylammonium salt (DL-EA salt), propylammonium salt (DL-PA salt), isopropyl ammonium salt (DL-IPA salt), t-butylammonium salt (DL-TBA salt), and 1, 1, 3, 3-tetramethylbutylammonium salt (DL-TMB salt). The free energies of formation of racemate and the binary phase diagrams of melting point indicated that DL-TBA salt is racemic solid solution at the melting point, and other DL-salts formed racemic compound. However, it was found by the inspection of infrared spectra of DL- and D-AM salts, the solubilities, and the ternary phase diagram that DL-AM salt existed in conglomerate at around room temperature. The optical resolution of DL-AM salt was feasible in methanol, ethanol, 1-propanol, and 2-propanol at 10 or 25°C for the racemic solutions with degrees of supersaturation of 110 and 120%, although the stereochemical outcome in methanol was very poor. The optical resolutions by successive preferential crystallizations of DL-AM salt were also achieved in ethanol at 10°C, and in 1-propanol at 25°C, and the D- and L-AM salts with optical purity of over 90% were obtained. The thermodynamic properties of these saturated alcoholic solutions of DL-and D-AM salts were also studied. It was possible to regard the ethanol, 1propanol, and 2-propanol solutions as being the regular solution, but it was not the case with the methanol solutions. In the methanol solution, a very strong interaction may exist between methanol and AM salt. The optical resolutions mentioned above suggest that such an interaction in the methanol solution poorly affects the optical resolution of DL-AM salt.
This article cannot obtain the latest cited-by information.
