A Simple Method for the Purification of Crude Hexanitrohexaazaisowurtzitane (HNIW or CL20)

A simple method for purifying crude hexanitrohexaazaisowurtzitane (HNIW or CL20) to analytical purity is described. This involves filtering a solution of HNIW in heptane / ethyl acetate through a column of Darco activated carbon type G-60 (∼20 g carbon/g HNIW). The method works extremely well for HNIW derived from 4,10-diformyl-2,6,8,12-tetraacetylhexaazaisowurtzitane (final purity>99.95%, ∼90% recovery), and reasonably well for HNIW derived from 4,10-dibenzyl-2,6,8,12-tetraacetylhexaazaisowurtzitane.