GAS-PHASE HYDROGENOLYSIS MEDIATED BY ACTIVATED CARBON - MONOSUBSTITUTED BENZENES

Easy hydrogenolysis of benzene derivatives in flow reactors packed wit h activated carbon (AC) and hydrogen as a bath gas is reported. Fast d esubstitution (below 600 degrees C) - PhX --> PhH - is encountered for chloro-, bromo-, and iodobenzene, modest for X = OCH3, NO2 and CH3, a nd slow for X = NH2, F, OH, CN and Ph. In general, compared with homog eneous hydrogenolysis, AC lowers the reaction temperature for complete conversion with 200 degrees C. As to the mechanism, hydrogen transfer s from hydroaryl and/or dihydroarene type surface groups appear to pla y a role in the displacement of X from aryl-X. The relatively fast con version of chloro-, bromo- and iodobenzene is explained by a process i n which an adsorbed substrate adds to a hydroaryl-type stabilized radi cal present on the AC surface, with elimination of the substituent as X. Copyright (C) 1996 Elsevier Science Ltd