the product on the filter was washed with 20 ml of cold absolute ethanol and the wet solid dried under vacuum at 70 u00b0 c for 18 hours until a kf value less than 4 was attained the pxrd and ir spectra of the obtained product are shown in fig1 a and 2 a respectively 20 g of crude rifaximin containing an average quantity of water of between 4 and 7 were placed in a reaction flask in which 0 2 g of ascorbic acid and 200 ml of absolute ethanol were added the suspension was heated to 40 u00b0 c with stirring until completely dissolved the solution was allowed to cool to 18 u00b0 c maintaining stirring for a further three hours after precipitation the suspension was left for a further 2 hours with stirring at a temperature of 8 u00b0 c then filtered the product on the filter was washed with 20 ml of cold absolute ethanol and the wet solid dried under vacuum at 60 u00b0 c for 18 hours until a kf value less than 4 was attained the pxrd and ir spectra of the obtained product are shown in fig1 b and 2 b respectively the dissolution profile of the substance in amorphous form was also determined and compared with that of the substance in crystalline form it was found that the amorphous form easily dissolves in ethanol even without stirring while the crystalline form is less wettable moreover with regard to water solubility.