The present invention relates to an improved process for the preparation of asulfinyl compound of formula (I), or a pharmaceutically acceptable salt,hydrate or solvate thereof, from a sulfide compound of formula (II), whereinin both formulae (I) and (II) R1 and R3 are selected from the group consistingof hydrogen, methyl or C1-4alkoxy, R2 is selected from the group consisting ofsubstituted or unsubstituted C1-4alkoxy and R4 is selected from the groupconsisting of hydrogen or substituted or unsubstituted C1-4alkoxy.
