FACILE HYDRODEHALOGENATION WITH HYDROGEN AND PD C CATALYST UNDER MULTIPHASE CONDITIONS/

A multiphase system consisting of a hydrocarbon solvent, a strong alka line solution, and a quaternary onium salt, in the presence of a Pd/C catalyst with hydrogen at atmospheric pressure, allows the rapid and p rogressive displacement of the chlorine atoms from polyhalogenated ben zenes. The onium salt in this case constitutes a third liquid phase in which the reaction takes place. At 50-degrees-C, 1,2,4,5-tetrachlorob enzene is reduced to benzene in 30 min using a Pd/Cl molar ratio of 1/ 130. Halogenated compounds are partitioned between the hydrocarbon sol ution and the liquid phase of the phase-transfer agent; rapid removal of HCI adsorbed on Pd/C is effected by neutralization with the alkalin e solution. The enhancement of the reaction rate compared with the kno wn methods might be attributed to the facile adsorption of H-2 by the catalyst under the reaction conditions. Different reaction rates resul t in the reduction of the three isomeric chlorotoluenes, whether the r eaction is carried out in the presence or absence of the onium salt.