1987 Volume 60 Issue 3 Pages 947-952
The racemic structures of the ammonium salts (AM salts) and seven organic ammonium salts of N-acetyl-DL-2-aminobutyric acid (DL-AcAbu) and N-acetyl-DL-norvaline (DL-AcNva) were studied on the basis of thermodynamic analyses to explore the possibility of optical resolution by preferential crystallization. An empirical equation has been derived from thermodynamic data at melting points of ammonium and organic ammonium salts of N-acyl-DL-amino acids to predict racemic structures around room temperature. The AM salts of DL-AcAbu and -AcNva exist in conglomerate around room temperature. It is possible to resolve optically these DL-AM salts by preferential crystallization in ethanol at 10 °C, and the successive preferential crystallization followed by purification gave D- and L-2-aminobutyric acids and -norvalines with optical purities close to 100%.
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