Catalytic deuteration of cyclohexanone and allied reactions over platinum metals

Abstract

In order to gain some insight into the mechanism of ketone hydrogenation to alcohol, cyclohexanone was deuterated over platinum metal catalysts under elevated pressure at 80 °C. The straightforward addition of two deuterium atoms to the carbonyl linkage was predominant over the heavy triad (Os, Ir, Pt). In contrast, the deuteration over the light triad (Ru, Rh, Pd) was accompanied by considerable isotopic exchange at the C-2 or C-6 position, leading to substantial proportions of the polydeuterated alcohols. A mechanism for cyclohexanone hydrogenation is presented which consists of three interlinked hydrogenation paths each having a different half-hydrogenated intermediate. The deuterium incorporation into the C-2 or C-6 position is attributable to alternation between the 1-monoadsorbed and 1,2-di-adsorbed intermediates.