To the reaction flask, 100 g of bisphenol A and 500 mL of methanesulfonic acid were added and stirred until completely dissolved to form a dark red solution. The reaction was continuously stirred at room temperature for 96 hours. Upon completion of the reaction, the reaction solution was slowly poured into 600 mL of ice water, cooled to room temperature and diafiltrated. The collected solid was washed well with deionized water. The washed solid was dissolved in ethanol and hot water at 50 °C under reflux conditions. Subsequently, methanol was added dropwise to the solution until no solids were precipitated, and the solution was immediately thermofiltered. The filter cake was washed several times with hot water and finally the product was dried under suitable conditions to give 45 g of a nearly white flocculent solid, 3,3,3',3'-tetramethyl-2,2',3,3'-tetrahydro-1,1'-spirobi[indene]-6,6'-diol (MSPINOL), in more than 99% yield.
