Preparation of diazobenzene nitrate (benzenediazonium nitrate)
Owing to the highly explosive nature of the diazobenzene nitrate, its preparation should never be undertaken in large quantities.
20 g of aniline are placed in a beaker, well cooled, and “boiled-out” nitric acid, previously diluted with half its volume of water, carefully added till the mixture sets to a thick crystalline paste – aniline nitrate. The crystalline mass is filtered off at the pump, and washed with a little cold water. 5 g of the moist salt are finely powdered and placed in a small flask with enough water just to cover the substance. The flask is now well cooled in ice-water, and nitrous fumes are led in with frequent agitation until all the aniline nitrate has disappeared. At no time must the temperature of the flask rise above 10°C. Should there not be sufficient water to keep all the diazobenzene nitrate formed in solution, its crystalline form will easily enable it to be distinguished from the aniline salt. When the reaction is finished the content of the flask are poured into 3 times their volume of absolute alcohol, and ether is added to this mixture as long as crystals separate. If too much water has been added to the aniline nitrate from the beginning, a thick aqueous solution of diazobenzene nitrate separates out in place of the crystals. If this occurs, the ether-alcohol is decanted off, and the residue redissolved in absolute alcohol, and reprecipitated with ether. On no accation must large quantities of the preparation be allowed to dry. If it has to be preserved it must be kept moist, or, better, in aqueous solution. The usual diazo reactions can be carried out with the latter. Diazobenzene nitrate forms colorless needles ; extremely explosive in the dry state ; Very soluble in water ; insoluble in ether ; on heating decomposes explosively.
Systematic organic chemistry, by W. M. Cumming, 375-376, 1937.