The hydrogenation of aromatic quarternary ammonium and related compounds.

The hydrogenation of a number of aromatic quarternary ammonium compounds has been studied. The hydrogenations were performed at 30C. and 1 atmosphere pressure, over Adams platinic oxide catalyst, in an aqueous ethanol solvent. The hydrogenation of trimethylphenylammonium chloride occurs in two stages: i) hydrogenolysis of the carbon-nitrogen bond ii) ring hydrogenation of the aromatic hydrocarbon formed. Both reactions are first order with respect to the catalyst and zero order with respect to the substrate. The rate of hydrogenolysis is reduced by addition of benzene to the reaction mixture, and by an increase in the acid concentration of the solvent. The toxicity of piperidine is less to the hydrogenolysis than to the ring hydrogenation. Substitution in the meta or para positions of the phenyl group reduces the rate of hydrogenolysis, but substitution in the ortho position increases the rate of hydrogenolysis. An increase in the size of the alkyl groups also decreases the rate of hydrogenolysis. The hydrogenation of benzyltrimethylammonium chloride is similar but substitution in any position of the aromatic ring reduces the rate of hydro-genolysis. The hydrogenations of benzyl fluoride and fluorobenzene also occur in two stages, an aromatic hydrocarbon being produced as an intermediate.