Into a 100 ml four-necked flask were charged 25.47 g of 1,1-bis(4-hydroxy-3-methylphenyl)-1-phenylethane["Bis-OC-AP" manufactured by Honshu Kagaku Co., Ltd.], 4.48 g of sodium hydroxide and 44.8 g of water. While stirring at 50° C., 25.97 g of 37% formaldehyde was added dropwise thereto over 1 hour, and the reaction was conducted for 1 more hour. After completion of the reaction, 11 g of 90% aqueous acetic acid solution was added for neutralization and then the mixture was cooledto 25° C. Thereafter, 100 g of ethyl acetate and 20 g of toluene were added thereto and a phase separation was carried out. Then, the resulting mixture was concentrated to obtain 30.2 g of 1,1-bis(4-hydroxy-3-hydroxymethyl-5-methylphenyl)-1-phenylethane. Purity measured by liquid chromatography (LC): 85%
