Hydrogenation and Hydrogenolysis. X. The Hydrogenation of Methoxy- and Ethoxyanilines with Rhodium Catalysts

Hydrogenation of methoxy- and ethoxyanilines with a ruthenium catalyst was investigated at 80°C under the hydrogen pressure of 80–100 kg/cm2. The amount of hydrogenolysis which occurred during hydrogenation varied with solvent from 35.1% in methanol to 8.5% in t-butyl alcohol in the hydrogenation of p-methoxyaniline. With use of t-butyl alcohol as solvent, good yields of methoxy- and ethoxycyclohexylamines were obtained from corresponding alkoxyanilines. It was shown that the rate of formation of cyclohexylamine increases with increasing polarity of solvent. m-Alkoxyanilines were found to hydrogenolyze more readily than the corresponding ortho or para isomers. For the greater tendency of meta isomers toward hydrogenolysis, an explanation based on the ionic cleavage of the carbon-oxygen bond was suggested.