Patent ID: 7411088

Claim:
A process for the preparation of a compound of formula (1): wherein R represents H or an alkali metal, Ar 1 represents 4-chlorophenyl and Ar 2 represents 2,5-difluorophenyl; comprising the steps of: (a) stirring a mixture of a cis-sulfide of formula (2) and a trans-sulfide of formula (3): with 4-chlorobenzenethiol in an acidic medium in which said mixture of sulfides is partially soluble, causing preferential crystallisation of cis-sulfide of formula (2); (b) collecting the cis-sulfide of formula (2); (c) oxidising the cis-sulfide of formula (2) to the corresponding sulfone; and optionally (d) neutralising the product of step (c) with alkali.