Metal-catalyzed hydrogen exchange between pyridine and deuterium

Abstract

The hydrogen exchange reaction between pyridine and molecular deuterium has been investigated using films of Mn (62 °C), Co (54–84 °C), Ni (42–95 °C), W (62 °C), and powdered Ir (−14–101 °) and Pt (100 °C) as catalysis. The activities of these metals fall in the sequence Co ~ Ni ~ Ir ~ Pt > Mn > W, tungsten showing very low activity under the conditions used. All of these metals catalyzed the exchange of the hydrogen atoms at positions 2 and 6 in pyridine (pair exchange). Exchange of hydrogen atoms at all positions (extensive exchange) occurred over freshly prepared Ni at 60 °, Ir at 48 °, and Pt at 100 °C. Activity diminished when catalysts were repeatedly used; for an iridium powder the activity for the exchange of hydrogen atoms at the 3-, 4-, and 5-positions was poisoned more rapidly than the activity for exchange at the 2- and 6-positions. Nickel film at 95 °C and platinum powder at 100 °C each catalyzed the hydrogenation of pyridine to piperidine. The nickel-catalyzed exchange of 2- and of 3-methylpyridine with deuterium is reported briefly. A mechanism for the exchange reaction is proposed.