acid and most preferably it is succinic acid the therapeutically acceptable acid addition salts of formula i hx are prepared by reacting the base form of 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine or a substituted 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine with one or more equivalents preferably with an excess of the appropriate acid in an organic solvent such as ethanol for example these compounds can be prepared as outlined in the following scheme str10 wherein y is cl or c o och 3 r 4 is ch 3 str11 can also be str12 a precursor of the synthesis of compounds of formula i and formula i hx is 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine see u s pat no 4 230 856 which is obtained by means of reduction of 3 4 dihydropyrrolo 1 2 a pyrazine see u s pat no 4 216 321 tetrahydropyrrolo 1 2 a pyrazine iv reacts with an ethanol solution of succinic acid to form 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine hydrosuccinate iii 2 acetyl 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine ii r 3 ch 3 and 2 benzoyl 1 2 3 4 tetrahydropyrrolo 1 2 a pyrazine ii r 3 c 6.