Aromatic heterocyclic derivatives have the formula ##STR1## wherein R.sub.1 represents (i)--CH.sub.3, (ii)--CH.sub.2 OH or (iii) ##STR2## wherein R.sub.3 represents hydrogen, --OR.sub.4 wherein R.sub.4 represents hydrogen, alkyl having 1-20 carbon atoms or mono- or polyhydroxyalkyl or R.sub.3 represents ##STR3## wherein r' and r" represent hydrogen, lower alkyl or together form a heterocycle, R.sub.2 represents hydrogen or --CH.sub.3 and Ar represents ##STR4## wherein Z is O or S, ##STR5## wherein R.sub.5 is lower alkyl or ##STR6## wherein R.sub.6 is hydrogen or alkyl having 1-10 carbon atoms and R.sub.7 represents alkyl having 4-12 carbon atoms or cycloalkyl, Y is CH or a nitrogen atom and X represents oxygen, sulfur or --N--R.sub.8 when R.sub.8 represents hydrogen, lower alkyl or lower alkoxycarbonyl, with the proviso that (i) when Y is CH and X is oxygen or sulfur Ar is other than C and (ii) when Y is nitrogen and X is oxygen, Ar is other than (C) or (D) in which R.sub.6 is alkyl having 1-4 carbon atoms and R.sub.7 is branched alkyl having 4-12 atoms.