Abstract2‐Halopyridines1a‐dreacted with sodium thiophenoxide in DMF at 80° to afford theipso‐substitution products. The following relative order of reactivity was observed: 2‐iodopyridine (1a) ∼2‐bromopyridine (1b) ≫2‐chloropyridine (1c) ∼ 2‐fluoropyridine (1d). The reaction of1bis inhibited by the electron scavenger azobenzene and by the radical scavenger benzoqoquinone. Furthermore, results of the reaction of 3‐bromopyridine (2b) serve to rule out pyridyne mechanism. It is reasonable to suggest therefore that the reaction proceeds through the radical chain process containing one electron