Process for purifying tetrachlorophthalic anhydride and high-purity tetrachlorophthalic anhydride

摘要

In the purification of crude tetrachlorophthalic anhydride containing hexachlorobenzene as impurities, this invention relates to purification by decomposition in which crude tetrachlorophthalic anhydride is contacted with chlorine gas in fuming sulfuric acid or sulfuric anhydride in the presence of iodine or iodine trichloride to decompose the impurities and remove them or purification by washing in which hexachlorobenzene is separated by washing with a chlorinated solvent. This invention also relates to a process for purifying crude tetrachlorophthalic anhydride containing iodotrichlorophthalic anhydrides as impurities by applying a radical reaction treatment in a chlorinated solvent to convert iodotrichlorophthalic anhydrides to tetrachlorophthalic anhydride. Moreover, it relates to high-purity tetrachlorophthalic anhydride containing 10 ppm or less of hexachlorobenzene. With the process of this invention, it is possible to recover high-purity tetrachlorophthalic anhydride with extremely low contents of impurities readily in high yield.