The reaction between a fatty acid RCOOH and a diamine H 2 NCH 2 CH 2 NHR, wherein R represents an aliphatic group comprising from 8 to 22 carbon atoms and R, represents a substituted or unsubstituted alkyl or alkenyl group comprising from 1 to 4 carbon atoms so as to produce an imidazoline is carried out using a moderate initial excess of diamine and when necessary reducing the pressure logarithmically with respect to time until the reaction is completed.
The formation of undesirable diamide impurities is avoided while using economic quantities of diamine and non-specialised equipment. The processes can be carried out without any monitoring of the progress of the reaction by skilled personnel being required and if through error progress is unsatisfactory a single readjustment can serve to carry the reaction to completion.