Jelaskan Nitrasi ipso dari Nitrasi

With aryl chlorides, triflates and nonaflates ipso substitution can take place as well in so-called ipso nitration. The phrase was first used by Perrin and Skinner in 1971 in an investigation into chloroanisole nitration  In one protocol 4-chloro-n-butylbenzene is reacted with sodium nitrite in t-butanol in presence of 0.5 mol% Pd2(dba)3, a biarylphosphine ligand and a phase-transfer catalyst to 4-nitro-n-butylbenzene