A mixture of 30.0 g (67.5 mmol) of di-(2,2,6,6-tetramethyl-piperidin-4-yl) phthalate, 27.5 g (214 mmol) of 70% aqueous t-butyl hydroperoxide, 2.0 g of molybdenum trioxide, and 200 ml of cyclohexane is heated to reflux. Water is collected in a Dean-Stark trap. After 75 min., the reaction mixture becomes red. Another portion of t-butyl hydroperoxide (42.5 g, 70%, 330 mmol) is added over 30 minutes. After the additional water is collected, the reaction mixture is transferred to a Fischer-Porter bottle and heated at 140° C. for 4.5 hours. The nearly colorless reaction mixture is treated with 6.9 g (90%, 69 mmol) of t-butyl hydroperoxide and heated at 140° C. for 90 minutes to remove the last traces of pink color. The reaction mixture is cooled, filtered, and stirred with a solution of 43 g of sodium sulfite in 530 ml of water for 2 hours. Dichloromethane (600 ml) is added, and the organic layer is separated, dried over magnesium sulfate, and concentrated to obtain a crude solid. Purification (Waters Prep. 500A HPLC, 25:1 heptane:ethyl acetate) affords 31.0 g (72% yield) of a white solid, m.p. 149°-51° C.
