PURPOSE: To obtain the title high-quality compound by subjecting an alkaline (earth) metallic salt of dicarboxybenzenesulfonic acid and a phosphonium salt to double decomposition reaction in an aqueous solvent in the presence of a given amount of free sulfonic group.
CONSTITUTION: An alkaline (earth) metallic salt of 3,5-dicarboxybenzenesulfonic acid and 90-100mol% (based on total sulfonic group) compound shown by formula I (R1 to R4 are 1-18C alkyl, phenyl or benzyl; X- is anion) are subjected to double decomposition reaction in an aqueous solvent (preferably water alone) containing ≥50wt.% in the presence of a given amount of free sulfonic group in an amount corresponding to 1-5mol% total sulfonic group in the alkaline (earth) metallic salt of 3,5-dicarboxybenzenesulfonic acid at room temperature - 80°C, filtered under pressure and purified to give the aimed compound shown by formula II.
NISHIO HIROSHI
SUGIURA FUMITOSHI
