If nicely crystalline, recrystallise it from Et2O/pentane or pet ether (b 40-60o). Alternatively dissolve it in diisopropyl ether (dried over CaCl2 for 24hours, then over P2O5 for 24hours) by shaking and warming (for as short a period as possible), and filter warm. Cool to ca 45o, then slowly to room temperature and finally at 5o for more than 2hours. Collect the solid, wash it with cold dry diisopropyl ether and dry it in a vacuum over Ca(OH)2 and NaOH. Store it dry in a desiccator in the dark. Solutions can be stabilised with 2% CaCO3. [Redemann & Niemann Org Synth 65 236 1987, Coll Vol III 11 1955, Beilstein 17/6 V 368.]
