ChemInform Abstract: Facile Hydrodehalogenation with H2 and Pd/C Catalyst Under Multiphase Conditions. Part 2. Selectivity and Kinetics

Hydrodehalogenation of polyhalogenated aromatics with Pd/C catalyst carried out in the presence of a quaternary onium salt follows zero-order kinetics in the substrate and first-order kinetics in the Pd/C catalyst; the related rate constants were determined for o-, m- and p-bromotoluenes, o-, m- and p-chloroalkylbenzenes (methyl, ethyl, and propyl derivatives), and other aryl halides. Reaction rates, depending on the aromatic to be reduced, may be strongly enhanced by the presence of quaternary onium salts: the isomeric chloroethylbenzenes were reduced SO times faster when operating in the presence of Aliquat 336 (1). Also the hindered 2-chloro-m-xylene easily yielded m-xylene