Aqueous ammonia has been found to be a good and versatile medium for the highly selective hydrodehalogenation of polyfluoroarenes by zinc under unprecedentedly mild conditions. The reduction of pentafluorobenzoic acid, 2, 3, 4, 5, 6-pentafluorobenzyl alcohol, pentafluorobenzamide, pentafluoropyridine, heptafluoro-2-naphthoic acid, 1, 3, 4, 5, 7, 8- hexafluoro-2-naphthoic acid, octafluoronaphthalene, octafluorotoluene, ...