The cyclocondensation of N,N'-bis(3,4-dichlorobenzylidene)ethylenediamine (I) with 2-sulfanylacetic acid (II) in refluxing toluene gives a mixture of the meso (R,S)-isomer and the corresponding racemate (R,R)+(S,S), which is easily separated by HPLC on a Chiracel OD column to obtain the target meso (R,S)-isomer.