Purify it by recrystallisation from dimethylformamide. The purity is checked by paper chromatography, RF 0.90 [i-PrOH/saturated (NH4)2SO4/H2O, 2:79:19 as eluent], IR (KBr) 16201570 ( C=C, C=N) and max 1253 (P=) cm-1.[Takaku et al. ull Chem Soc Jpn 47 779 1974.]
