IN WHICH R1 and R2 each stands for a hydrogen atom or together they stand for the group -CH CH-CH CH- which may carry one or more lower alkyl, halogeno-alkyl or alkoxy groups, halogen atoms or NO2-groups, and R3 and R4, independently of one another, each stands for a hydrogen atom, a lower alkyl, halogeno-alkyl, alkoxy or halogeno-alkoxy group, a halogen atom or NO2 or together they stand as a -CH CH-CH CH- group with the benzene nucleus for the naphthyl group, AND PHYSIOLOGICALLY ACCEPTABLE ACID ADDITION SALTS THEREOF, PROCESS FOR PREPARING THEM AND PHARMACEUTICAL COMPOSITIONS CONTAINING THEM AS ACTIVE SUBSTANCE.