When an organic solvent is used for preparing it, a solution, which is prepared by dissolving any of the above-mentioned phenolic compounds in an ordinary organic solvent such as methanol, ethanol or acetone is mixed with a water-soluble microbicide such as Cl-MIT or with a mixture containing a water-soluble microbicide such as Cl-MIT and some impurities, etc., and reacted with the water-soluble m