Selectivity issues in the catalytic multiphase hydrodehalogenation of functionalized halo-aromatics over Pd/C, Pt/C, and Raney-Ni

The multiphase system, consisting of a biphasic isooctane-aqueous medium, a heterogeneous catalyst, and a quaternary ammonium salt (Aliquat 336)—a supported ionic liquid catalyst surface modifier—allows efficient hydrodehalogenation under mild conditions (50 ◦C and 1 atm H2). In the reactions of various halogenated benzenes, nitrobenzene, benzonitrile, benzaldehyde in the multiphase catalytic system, the selectivity of reduction of certain groups (hydrodehalogenation, carbonyl hydrogenation, hydroxyl hydrogenolysis, aromatic reduction) is a function of the presence of a phase-transfer agent, pH of the aqueous phase, catalyst choice (5% Pd/C, 5% Pt/C or Raney-Ni). The suggested mode of action of the quaternary salt involves the formation of a distinct ionic liquid layer at the catalyst–solution interface, where the reaction proceeds with alternative selectivity.