for their preparation and the use thereof in the manufacture of medicinal preparations for the oral or topical route the process of the present invention comprises reacting one molar equivalent of rifamycin o with an excess of 2 amino 4 methylpyridine preferably from 2 0 to 3 5 molar equivalents in a solvent mixture consisting of water and ethyl alcohol in volumetric ratios between 1 1 and 2 1 for a time between 2 and 8 hours at a temperature between 40 u00b0 c and 60 u00b0 c after completion of the reaction the reaction mass is cooled to room temperature and added with a solution of ascorbic acid in a mixture of water ethyl alcohol and aqueous concentrated hydrochloric acid under strong stirring in order to reduce the small amount of oxidized rifaximin that forms during the reaction finally the ph is adjusted to about 2 0 by further addition of hydrochloric acid concentrated aqueous solution in order to better remove the excess of 2 amino 4 methylpyridine used in the reaction the suspension is filtered and the resulting solid is washed with the same solvent mixture water ethyl alcohol as used in the reaction such semifinished product is called u201c raw rifaximin u201d the raw rifaximin can be directly submitted to the subsequent purification step alternately in case long times of preservation of the semifinished product are expected the raw rifaximin can be dried under vacuum at a temperature lower than 65 u00b0 c for a time.