Benzene diazonium chloride is prepared by the reaction of aniline with nitrous acid at 273−278K which is known as diazotisation.
Due to its instability, the diazonium salt is not generally stored and is used immediately after its preparation. C6H5NH2+NaNO2+2HCl273−278KC6H5N2+Cl−+NaCl+2H2O
Temperature must vary from 0−5∘C.