The invention relates to a method for the synthesis of exocyclic derivatives of cycloalkyl-hydrazines and exocyclic derivatives of heterocycloalkyl-hydrazines The invention is characterised in that the method comprises a step consisting in demixing a solution containing said synthesised derivative, by reacting a heterocyclic amine with monochloramine, in an organic phase and an aqueous phase with the addition of anhydrous sodium hydroxide. According to the invention, the starting amine which has not reacted is collected and reused directly without any additional treatment. The inventive method can also be used to obtain the corresponding exocyclic heterocycloalkyl-hydrazine or cycloalkyl-hydrazinederivative derivative at a low cost compared to that of other known methods.