A Convenient and Safer Synthesis of Diaminoglyoxime

A new procedure for the synthesis and isolation of diaminoglyoxime (DAG) is described. A previous procedure involved treating glyoxal with 2 equiv each of hydroxylammonium chloride and sodium hydroxide to form glyoxime, followed by further treatment of this intermediate with two additional equivalents of hydroxylammonium chloride and sodium hydroxide at 95 °C to form DAG. Two recrystallizations were needed to obtain the desired product in pure form. Another previous procedure employed glyoxal in the presence of 4 equiv each of hydroxylammonium chloride and sodium hydroxide at 95 °C to form DAG. Though this latter procedure gives product after a few hours, yields do not exceed 40%, and the reaction is prone to thermal runaway. Furthermore, the use of decolorizing carbon and recrystallization of the crude solid are necessary to obtain a pure product. The new disclosed procedure involves treating a preheated aqueous hydroxylamine solution (50 wt %, 10 equiv) with aqueous glyoxal (40 wt %), followed by heating at 95 °C for 72–96 h. The reaction is cooled to room temperature and then to 0–5 °C to obtain DAG in pure form, without recrystallization or decolorizing carbon in 77–80% yield. The exothermic nature of the reaction is also minimized by this updated process.