Hydrogenolysis of aryl halides by hydrogen gas and hydrogen transfer over palladium-supported catalysts

In the present work, the influence of the hydrogenolysis method (hydrogen gas or hydrogen transfer) as well as of the nature of the hydrogen donor (HCOOK or 2-propanol) on the results found for hydrodehalogenation of aryl halides is discussed. Potassium formate hydrogen transfer competitive reactions confirm the strong adsorption of iodobenzene over the catalyst, which inhibits the adsorption of the other aryl halides and of the hydrogen donor. However, when using propan-2-ol as donor, iodobenzene is easily hydrodehalogenated and even fluorobenzene can be reduced. As for liquid-phase hydrogenolysis by hydrogen gas, results indicate that reactivity order (BrBz > ClBz > IBz > FBz) depends on both the C-X bond dissociation energy and the adsorption strength of the halobenzene. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.