The general procedure for the synthesis of (pyridin-2-ylmethylene)bis(4,1-phenylene)bis(sodium sulfate salt) from 4,4'-(pyridin-2-ylmethylene)bisphenol was as follows: the crude product of 4,4'-(pyridin-2-ylmethylene)bisphenol was dissolved in pyridine, and 39.5 g of chlorosulphonic acid was added slowly dropwise over the temperature range from 0 to 10°C. The reaction was carried out with continuous stirring. After the dropwise addition, the temperature was gradually increased to the reaction temperature and the reaction was continuously stirred for 1 hour. Subsequently, the reaction mixture was allowed to stir naturally at room temperature for 4 hours. Upon completion of the reaction, the reaction mixture was slowly poured into ice water and the pH was adjusted to 10 with 6 M sodium hydroxide solution. extraction was carried out with dichloromethane and the aqueous phase was separated and concentrated under reduced pressure. Finally, the product was collected by filtration and dried under vacuum at 40 °C to afford 34.8 g of sodium 4,4'-(pyridin-2-ylmethylene)diphenylsulfite, the product was a white solid with 99.8% purity and 86.4% yield.
