Impurities include tetramethylurea, dimethylamine, tetramethylethanediamine and tetramethyloxamide. It is washed with water while being flushed with nitrogen to remove dimethylamine, dried over molecular sieves, then passed through a silica gel column (previously activated at 400o) under nitrogen. De-gas it in a vacuum line by distillation from a trap at 50o to one at -70o. Finally, it is stirred over sodium-potassium alloy for several days. [Holroyd et al. J Phys Chem 89 4244 1985, Wiberg Angew Chem Int Ed Engl 7 766 1968, Beilstein 4 IV 167.]
