Process for Preparing and Conversion of Ilaprazole Crystalline Form A, B

Disclosed are novel processes for preparing crystalline forms A and B of ilaprazole of formula 1 and the conversion of these crystalline forms. The novel processes include a process of preparing the crystalline form A of high purity by preparing an inorganic salt of ilaprazole or a hydrate thereof and then neutralizing the prepared inorganic salt of ilaprazole or the hydrate thereof with an acid in an organic solvent (single solvent or mixed solvent) a process of preparing the crystalline form B of high purity by removing impurities from ilaprazole using an organic solvent (single solvent or mixed solvent); and a process of conversion from the crystalline A into the crystalline form B or from the crystalline form B into the crystalline form A.