Patent ID: 8247523

Claim:
A method for producing a purified 2-aryl-3,3-bis(4-hydroxyaryl) phthalimidine of formula (I) wherein R 1 is hydrogen or a C 1-25 hydrocarbyl group and R 2 is hydrogen, a C 1-25 hydrocarbyl group, or a halogen, and wherein the method comprises: heating a reaction mixture comprising a phenolphthalein compound of formula (II) wherein R 2 is hydrogen, a C 1-25 hydrocarbyl group, or a halogen, a primary aryl amine of formula (III), wherein R 1 is hydrogen or a C 1-25 hydrocarbyl group, and an acid catalyst, to form a phthalimidine compound of formula (I); precipitating the phthalimidine compound from the reaction mixture to provide a crude phthalimidine compound; dissolving the crude phthalimidine compound in an aqueous base solution; precipitating the dissolved, crude phthalimidine compound from the aqueous base solution by adding an acid in an amount effective to lower the pH of the solution to 9.0 to 12.0, to provide a semicrude phthalimidine compound; and isolating the semicrude phthalimidine compound from the aqueous base solution, to provide the purified 2-aryl-3,3-bis (4-hydroxyaryl) phthalimidine of formula (I), and having a phenolphthalein compound content of less than 2,500 ppm, based on the weight of the purified 2-aryl-3,3-bis(4-hydroxyaryl) phthalimidine.