#HNO_3, H_2SO_4# is the classic nitrating agent for benzene rings in that sulfuric acid protonates the nitric acid to form the electrophile #NO_2^+#, with which bromobenzene, as a nucleophile, reacts.
Both #"ortho- and para-nitrobromobenzene"# will result (the bromo group stabilizes the intermediates leading to these products), however, since #"para-nitrobromobenzene"# is less soluble, crystals of this material will be isolated.
#HNO_3 + H_2SO_4 rarr NO_2^+ + HSO_4^(-) + H_2O#
#C_6H_5Br + NO_2^(+) + HSO_4^(-) rarr p-C_6H_4NO_2Brdarr + H_2SO_4#
It is typical that the #"para"# derivative should be more insoluble than the #"ortho"#.
