PURPOSE: To produce readily handleable high-purity chloranil having a high specific gravity by chlorinating hydroquinone under mild conditions according to a simple method for operation.

CONSTITUTION: Hydroquinone is dissolved in a nonuniform mixed solvent of hydrochloric acid with an organic solvent incompatible therewith, e.g. a halogenated aromatic hydrocarbon such as dichlorobenzene and chlorine gas in a molar amount of 2.5 to 5 times based on 1mol hydroquinone is then fed to the nonuniform mixed solvent containing the hydroquinone. The feed of the chlorine gas is subsequently stopped and the chlorine gas is then refed to complete the reaction.