Cumene hydroperoxide (CAS NO. ) is purified by adding 100mL of 70% material slowly and with agitation to 300mL of 25% NaOH in water, keeping the temperature below 30 °C. The resulting crystals of the sodium salt were filtered off, washed twice with 25 mL portions of benzene, then stirred with 100mL of benzene for 20min. After filtering off the crystals and repeating the washing, they were suspended in 100mL of distilled water and the pH was adjusted to 7.5 by addn of 4M HCl. The free hydroperoxide was extracted into two 20mL portions of n-hexane, and the solvent was evaporated under vacuum at room temperature, the last traces being removed at 40-50 °C and 1mm. ether, but not diethyl ether, can be used instead of benzene, and powdered solid CO₂ can replace the 4M HCl.