Purification Methods
The free base is treated with saturated aqueous picric acid, allowed to stand for 12hours, filtered, washed with MeOH to remove the more soluble trans isomer and recrystallised from MeOH to give pure cis-picrate m 149-150o. The picrate (~5g) is shaken with 5M aqueous NaOH (50mL) and Et2O (150mL) while H2O is added to the aqueous phase to dissolve insoluble Na picrate. The Et2O extract is dried over solid NaOH and then shaken with Al2O3 (Merck for chromatography) until the yellow color of traces of picric acid disappears (this color cannot be removed by repeated shaking with 5-10 M aqueous NaOH). The extract is concentrated to 50mL and dry HCl is bubbled through until separation of the white crystals of the cis-HCl is complete. These are washed with Et2O, dried at 100o and recrystallised from EtOH/EtOAc to yield pure cis-hydrochloride m 182-183o (dried in a vacuum desiccator over KOH) with IR (KBr) 2920, 2820, 1582, 1470, 1445, 1410, 1395, max 1313, 1135, 1080, 990, 870 cm-1 . The pure free base is prepared by dissolving the hydrochloride in 10M aqueous NaOH, extracted with Et2O, dried over solid KOH, filtered and distilled in a vacuum. It has IR (film) max 2920, 2820, 2720, 2560, 1584, 1470, 1445, 1415, 1395, 1315, 1300, 1135, 1080, 1020, 990, 873 cm-1 . The 1HNMR in CDCl3 is characteristically different from that of the trans-isomer. [Armarego J Chem Soc (C) 377 1967, Gray & Heitmeier J Am Chem Soc 80 6274 1958, Witkop J Am Chem Soc 70 2617 1948, Skita Chem Ber 57 1982 1924, Helfer Helv Chim Acta 6 7991923, Beilstein 20 II 73, 20 III/IV 2026.]
