The invention comprises compounds of the general formula <FORM:0813173/IV (b)/1> in which Hal represents a halogen atom, R1 represents a hydrogen atom or a methyl group and R2 represents a hydrogen atom or an alkyl, alkenyl or hydroxyalkyl radical with 1 to 4 carbon atoms or a benzyl radical, and the acid addition salts of these compounds. Such are obtained by the introduction of the piperazine radical into the position para to the methyl group of toluenes of the formula <FORM:0813173/IV (b)/2> wherein (i) a para-toluidine of the formula <FORM:0813173/IV (b)/3> is reacted with diethanolamine or with a diethanolamine the amino group of which is substituted by a radical as defined for R2 or a reactive ester thereof, or (ii) a para-toluidine of the formula above reacted with ethylene oxide or an ethylene halogen-hydrin, the primary alcohol groups of the condensation product are transformed into reactive ester groups and the ester is then reacted with a primary amine or ammonia, or wherein (iii) a dihalogen-toluene of the formula <FORM:0813173/IV (b)/4> is reacted with piperazine or with an N-monoalkyl piperazine and the nitro group is reduced to an amino group, which is transformed into the diazonium group which is replaced by hydrogen by means of reducing agent. The reaction of the toluidine derivative with reactive esters of diethanolamine or the appropriately substituted diethanolamine is effected in the presence of an acid binding agent. Esters of hydrohalic, sulphuric and p-toluene sulphonic acids are suitable. Instead of the reactive esters as such there can be used mixtures of the diethanolamines with phosphorus or thionyl chlorides, aluminium chloride, p-toluene sulphonic acid and preferably mineral acid. In method (iii) alkylation either of the piperazine derivatives obtained directly on condensation of the 3-nitro-4-halogen toluenes with piperazine or of the productions obtained after replacing nitro by hydrogen may be effected. The products can be transformed into salts with, for example, hydrochloric, hydrobromic, phosphoric, sulphuric, amido-sulphonic, acetic, propionic, lactic, malonic, succinic, malic, tartaric, maleic, aceturic, hydroxyethane - sulphonic, nitric, benzoic and salicylic acids. In examples: (1) 2 - chloro - 4 - amino - toluene and methyldi-(chlorethyl) amine hydrochloride are reacted (in methanol with sodium carbonate) to give 1 - methyl - 4 - (31 - chloro - 41 - methylphenyl)-piperazine. From the appropriate reactants (with variations in conditions) there are prepared (2) 1 - (31 - chloro - 41 - methyl - phenyl)-piperazine and its maleate, and (3) 1-butyl - 4 - (31 - chloro - 41 - methyl - phenyl)-piperazine. In Example (4) 3-chloro-4-methyl-N : N-di-(b -hydroxy-ethyl)-amine (from the reaction of 2 - chloro - 4 - amino - toluene and ethylene chlorhydrin in the presence of quicklime) is reacted with phosphorus pentachloride, the 3 - chloro - 4 - methyl - N : N - di - (b - chlorethyl) aniline obtained being reacted with aminoethanol to give 1-hydroxyethyl-4-(31-chloro - 41 - methyl - phenyl) - piperazine; (5) 3 - chloro - 4 - methyl - N : N - di - (b - chlorethyl) aniline (prepared as in (4), or using ethylene oxide in place of chlorhydrin and/or phosphorus oxychloride) is reacted with ethylamine to give 1-ethyl-4-(31-chloro-41-methylphenyl)-piperazine. Similarly obtained (6 and 7) are the corresponding 1-allyl and 1-benzyl derivatives, and (8) 1-ethyl-4-(31-bromo-41-methyl - phenyl) piperazine (with 3 - bromo - 4-methyl - N : N - di - (b - hydroxyethyl) - aniline and 3 - bromo - 4 - methyl - N : N - di - (b chlorethyl) aniline as intermediates). In Example (9) 2-chloro-4-aminotoluene, diethanolamine and 48 per cent hydrobromic acid are heated together to give 1-(31-chloro-41-methylphenyl)-piperazine. In a generally similar manner there are prepared (10) 1-(31-bromo-41 - methyl - phenyl) - piperazine; (11) 1-(31 - fluoro - 41 - methylphenyl) - piperazine; (12) 1 - (31 - bromo - 21 : 41 - dimethyl - phenyl)-piperazine; (13) 1-(31-chloro-21 : 41-dimethylphenyl)-piperazine, which is subsequently ethylated with ethyl p-toluene sulphonate. In further examples: (14) 1-(31-chloro-61-nitro-41-methyl - phenyl) - piperazine hydrochloride (from 4 : 6 - dichloro - 3 - nitro - toluene and piperazine) is heated with methanol, hydrazine hydrate and Raney nickel to give 1-(31-chloro-41 - methyl - 61 - amino - phenyl) - piperazine. This is diazotized and the diazonium compound is reduced with hypophosphorous acid to 1-(31-chloro-41-methyl-phenyl)-piperazine; (15) 1-(31 - chloro - 61 - nitro - 41 - methyl phenyl) piperazine is ethylated, and the 1-ethyl-4-(31-chloro - 61 - nitro - 41 - methyl - phenyl) - piperazine resulting is converted by successive reduction with iron powder, diazotization of the amine and reduction with hypophosphorous acid to 1-ethyl-41-(31-chloro-41-methyl-phenyl) -piperazine; (16) 1-ethyl-4-(31-chloro-61-nitro-41 - methyl - phenyl) - piperazine is prepared by reacting 1-ethyl-piperazine with 4 : 6-dichloro-3-nitrotoluene and is subjected to further reaction as in (15).ALSO:A pharmaceutical preparation contains a piperazine derivative of the general formula <FORM:0813173/VI/1> in which Hal represents a halogen atom, R1 represents a hydrogen atom or a methyl group and R2 represents a hydrogen atom, or an alkyl, alkenyl or hydroxyalkyl radical with 1-4 carbon atoms or a benzyl radical, or an acid addition salt of the compound, in conjunction or admixture with a pharmaceutically suitable carrier. Salts mentioned are those with hydrochloric, hydrobromic, phosphoric, sulphuric, amido-sulphonic, acetic, propionic, lactic, malonic, succinic, malic, tartaric, maleic, aceturic, hydroxyethanesulphonic, citric, benzoic and salicylic acids. The preparations are used in the treatment of schistosoma mansoni infection and bilharzia.