Hydrogenation of stable nitroxyl radicals with acetylenic bonds on Ni, Pd, and Pt catalysts

Conclusions

• 1. We have examined the liquid-phase hydrogenation of stable iminoxyl radicals with acetylenic bonds — 4-ethynyl-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-phenylethylnyl-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl on Raney Ni, Pt, and Pd catalysts.

• 2. On Raney Ni the paramagnetic center and the C=C bond of the radicals are reduced simultaneously; in the presence of Pt the iminoxyl group is preferentially hydrogenated, while on Pd black the C≡C bond is reduced (via the olefinic compound) without affecting the paramagnetic center.

• 3. In the course of this work we have prepared several new stable iminoxyl radicals: 4-ethynyl-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-phenylethynyl-4-hydroxy-2,2, 6,6-tetramethylpiperidin-1-oxyl, 4-vinyl-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-(5-phenylvinyl)-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, and 4-(β-phenylethy1)-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, together with 4-vinyl-1,4-dihydroxy-2,2,6,6-tetramethylpiperidine and 4-ethyl-1,4-dihydroxy-2,2,6,6-tetramethylpiperidine.