The present disclosure relates to a process for preparing crystal modifications of racemic (2R,S)- and enantiomerically pure (2R)- resp. (2S)-DOTAP chloride (N,N,N-trimethyl-2,3-bis[[(9Z)-1-oxo-9-octadecenyl]oxy]-1-propanaminium chloride, also known as (Z,Z)-N,N,N-trimethyl-2,3-bis[(1-oxo-9-octadecenyl)oxy]-1-propanaminium chloride or 1,2-dioleoyloxy-3-trimethylammonium propane chloride) and the hydrates thereof, and to the use of the compound for the preparation of pharmaceutical compositions. The process has a recrystallisation step involving slow cooling at a rate of 0.001°C to 0.1°C per minute.
