Diazonium Formation - 1-(m-nitrophenyl)diazonium chloride
The synthesis of 1-(m-nitrophenyl)diazonium chloride from m-nitroaniline is a good example of the standard laboratory procedure for the transformation of an amine into a diazonium salt.
Concentrated hydrochloric acid (125 mL) and 250 mL of hot water are added to m-nitroaniline (138 g, 1.0 mol). The resulting solution is heated to 85 °C followed by the addition of 275 mL of concentrated hydrochloric acid. The reaction mixture is then cooled rapidly in a salt-ice bath. A solution of sodium nitrite (72 g, 1.05 mol) in 175 mL of water is then added slowly below the surface of the reaction mixture with stirring. The temperature of the reaction mixture is monitored to maintain the temperature below 0 °C. The resulting solution is then stirred for an additional 20 minutes followed by the slow addition of urea (5g) in 12.5 mL of water over 15 minutes to minimize foaming. The resulting solution of 1-(m-nitrophenyl)diazonium chloride is not isolated and should be kept cold until it used in a subsequent step.