Homogeneous and heterogeneous metal-catalysed hydrogen isotope exchange of nitrobenzene with tritium gas and tritiated water

Abstract

Hydrogen isotope exchange of nitrobenzene with tritium gas and tritiated water is studied over heterogeneous and homogeneous forms of platinum, palladium and nickel. Exchange with water is facile where homogeneous platinum and palladium salts are the catalysts but this is not the case over heterogeneous forms of the metals. In contrast, exchange with tritium gas is facile over heterogeneous platinum, palladium and nickel. Exchange in nitrobenzene is thus an indicator of homogeneous, as distinct from heterogeneous, exchange as previously claimed, only where the isotope source is water and not elemental hydrogen. Detailed isotope orientation patterns, determined by ³H NMR, are interpreted in terms of the type of absorption intermediate on the metal, and compared with those of aniline.