in diethyl ether react. of a soln. of POCl3 in ether with a suspension of anhydrous hydrazine in ether on cooling (ice-NaCl-mixt.) and stirring;; distn. of ether in vac. or high vac.; passing the aq. soln. through an anoin exchange resin (Dowex 2); evapn. in high vac.; addn. of cold ethanol at -12 °C, crystn.;;
