l sulfoxide; and mixtures of them with water. [0037] (The Second Step) [0038] In this step, a sulfonamide compound of formula (IV) is reacted with an acyl compound of formula (V) in the presence of a base to produce an acylsulfonamide compound of formula (I). [0039] In formula (V) for the acyl compounds used in this step, X represents a halogen atom such as chlorine or bromine atom, succinimido gr