Reaction of o-chlorobenzyl chloride (I) with thiourea (A) in refluxing ethanol affords the isothiourea hydrochloride (II), which is treated with chlorine gas in aqueous solution equal or lower at 10 C to afford the corresponding sulfonyl chloride (III). Exposure of (III) to liquid ammonia smoothly converts (III) to the sulfonamide (IV), which is converted to the sodium salt monohydrate with ethanolic sodium hydroxide.