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 g as or hydrogen transfer) as well as of the nature of the hydrogen donor (HC OOK or 2-propanol) on the results found for hydrodehalogenation of aryl hal ides is discussed. Potassium formate hydrogen transfer competitive reaction s confirm the strong adsorption of iodobenzene over the catalyst, which inh ibits the adsorption of the other aryl halides and of the hydrogen donor. H owever, when using propan-2-ol as donor, iodobenzene is easily hydrodehalog enated and even fluorobenzene can be reduced. As for liquid-phase hydrogeno lysis by hydrogen gas, results indicate that reactivity order (BrBz > ClBz > IBz > FBz) depends on both the C-X bond dissociation energy and the adsor ption strength of the halobenzene. (C) 2000 Academie des sciences / Edition s scientifiques et medicales Elsevier SAS.