Catalytic amounts of 70% perchloric acid (0.1-10, mostly 0.1-1, mol%, based on substrate) initiate the regioselective halogenation of activated aromatics [mesitylene, 1, 3- dimethoxybenzene, 2, 3-dimethylanisole, o-xylene] and heteroaromatics [thiophene, its 2- methyl, 2-halo (chloro, bromo, iodo), and 3-bromo derivatives] with N-halosuccinimide (NXS, X= C1 or Br) in two-phase solidliquid systems (NXS/hexane or NXS/CCW at room ...