A process for obtaining therapeutically active 2-[4-(3- and 2-(fluorobenzyloxy)benzylamino]propanamides, and their salts with pharmaceutically acceptable acids with high purity degree, in particular, with a content of dibenzyl derivatives impurities lower than 0.03%, preferably lower than 0.01% by weight. The process is carried out by submitting the Schiff bases intermediates 2-[4-(3- and 2-fluorobenzyloxy)benzylideneamino]propanamides to a reduction reaction with a reducing agent selected from sodium borohydride and potassium borohydride in an appropriate amount of an organic solvent selected from C 1 -C 5 lower alkanols, allowing the formation and presence during a substantial position of the reduction reaction course of a suspension of the Schiff base into the saturated solution of the Schiff base into the same organic solvent.