A PROCESS FOR PREPARING RIFAXIMIN K

The present invention relates to a process for obtaining rifaximin comprising the following steps: a) reacting rifamycin O with 2-amino-4-picoline in the presence of a solvent mixture comprising water and a solvent selected from methyl isobutylketone, ethylacetate and a water soluble solvent; b) obtaining a rifaximin solution by removing the aqueous phase; c) obtaining rifaximin from the rifaximin solution, wherein when the solvent is a water soluble solvent, either methyl isobutylketone or ethylacetate is further added in step a). In another aspect the process of the invention relates to a process for obtaining the crystalline form of rifaximin comprising the following steps: i) contacting rifaximin or a rifaximin solution with exclusively ethylacetate, ii) obtaining the rifaximin in crystalline form by removing ethylacetate.