Process for the preparation of halogen-substituted phthalic anhydrides

A process for the preparation of halogen substituted phthalic anhydrides of the formula: wherein X is a halogen, by the reaction of a halogen substituted tetrahydrophthalic phthalic anhydride of the formula: or a geminal dihalogen substituted hexahydrophthalic anhydride of the formula: in a vapor or melt phase while mixed with a halogen gas and in the presence of an activated carbon catalyst at an elevated temperature.