Abstract: Chlorodibenzo-p-dioxin impurities are removed from a polychlorophenol that contains at least one chlorodibenzo-p-dioxin as an impurity by preparing an aqueous solution of a water-soluble alkaline salt of the polychlorophenol, mixing the aqueous solution with cyclohexane to extract the dioxins therefrom, decanting the purified aqueous solution from the cyclohexane phase, neutralizing the purified aqueous solution to precipitate the purified polychlorophenol, and separating the precipitate.

Abstract: A technique is provided for employing an aqueous solution to treat a cellulosic or other substrate with a water-insoluble preservative such as a polychlorophenol and the like. The treatment solution is formed of water, a soluble polychlorophenate, and a suitable acid-former which, after a predetermined delay interval sufficient to allow adequate treatment with the polychlorophenate, progressively effects in in situ precipitation of the insoluble polychlorophenol on the substrate to be protected. The extent of the delay interval, as well as the extent of the precipitation time, may be regulated as a function of temperature, the excess alkalinity of the treatment solution, and the particular acid-former employed.