Reaction of 1,2-dibromoethane with primary amines: formation of N,N′-disubstituted ethylenediamines RNH–CH2CH2–NHR and homologous polyamines RNH–[CH2CH2NR]n–H

The reaction of primary amines RNH2 (R: Me, Et, iPr, tBu and Ph) with 1,2-dibromoethane gave N,N′-disubstituted ethylenediamines R–NH–CH2CH2–NH–R () in yields ranging from 10% (; R=Me) to 70% (, R=tBu; , R=Ph). Piperazines and N-substituted polyethyleneimines were identified (1H NMR, 13C NMR and EI-MS) as side products of the reaction and isolated by fractional distillation. The piperazines are formed in yields of 3–10% and can be separated from the diamines in all cases, except for R=Me and Ph. The polyamine homologues RNH–[CH2CH2NR]n–H () were isolated in yields ranging from 0.1% (n=4, R=iPr) to 14% (n=2, R=iPr). The yields of increase with the size of the substituent R, no obvious trend exists for the yields of the side products.