Regioselectivity in the Catalytic Hydrogenolysis of Cyclopropylamine

Abstract

The catalytic hydrogenolysis of cyclopropylamine [1] was studied in order to investigate the regioselective behavior of the amino group in the cyclopropane ring hydrogenolysis. The reaction was carried out over Pd-C or Raney Ni in heptane or methanol for 24 h at room temperature under the atmospheric pressure or at 70°C under 80 kg/cm². The hydrogenolysis of the cyclopropane ring occurred selectively at the bond adjacent to the amino group and gave propylamine [4], accompanying dipropylamine [5], N-propylcyclopropylamine [6]and tripropylamine [7] formed by the subsequent reductive alkylation. The reductive alkylation proceeded more easily by the use of Pd-C than by Raney Ni. On the other hand, when the reaction was carried out over Pd-C in CH₃COOH or H₂O containing HC1 in equimolar amounts to [1], the hydrogenolysis occurred mainly at the bond opposite to the amino group and gave mainly isopropylamine [3].
The observed differences seem to be ex plained by considering the predominant adsorbed states in the hydrogenolysis. The amino group behaves as an adsorbed group and causing the adsorption and the subsequent cleavage of the adjacent C₁-C₂ bond under the neutral conditions. On the other hand, under the acidic conditions, the hydrogenolysis of the opposite C₂-C₃ bond proceeds predominantly because the adsorption of the C₁-C₂ bond accompanying the ammonio group is sterically hindered by the ammonio group.