Gently heat the impure iodide with good grade Me2CO. The saturated solution obtained is decanted rapidly from undissolved salt and treated with an equal volume of dry Et2O. The iodide separates as flat needles which are collected by centrifugation, washed several times with dry Et2O, and dried in a vacuum over P2O5. For this recrystallisation it is essential to minimise the time of contact with Me2CO and to work rapidly and with rigorous exclusion of moisture. If the crude material is to be used, it should be stored under dry Et2O, and dried and weighed in vacuo immediately before use. [Landauer & Rydon J Chem Soc 224 1953, Hudson et al. J Chem Soc Perkin Trans 1 982 1974, Beilstein 6 IV 704.]
