Purify the free amino-acid by dissolving it in H2O and passing it through a Dowex 50W (acid form) column and eluting with 1M aqueous NH4OH. The eluate is evaporated (in vacuo) and the residue is dissolved in H2O. Me2CO is added to turbidity, cooled at 0o and the colourless crystals of the amino-acid are collected and dried in vacuo [Bernáth et al. Tetrahedron 41 1315 1958, cf Mazza & Crapetta Gazzetta 57 297 1927]. In earlier work, it was recrystallised from aqueous EtOH and had reported melting points of 265-265o [Kricheldorf Justus Liebigs Ann Chem 1378 1975] and 269-271o [Marconi & Mazzochi J Org Chem 31 1372 1966]. The hydrochloride [57266-56-5] M 177.6 has m 210-213o and the methyl ester hydrochloride [52766-61-2] has m 85-87o (from Et2O). The trans-(±)-(1RS,2RS)-amino-acid [97945-19-2] crystallises from aqueous Me2CO with m 267-269o. [Beilstein 14 II 203.]
