The industrial synthesis of tetrachlorophthalic anhydride mainly involves two methods:
Direct Chlorination of Phthalic Anhydride
Solvent Method: Using phthalic anhydride as a raw material, iodine or iodine chloride catalyst is added to fuming sulfuric acid or chlorosulfonic acid, and chlorine gas is passed through to carry out an electrophilic substitution reaction.
Melting Method: After phthalic anhydride is melted, it is directly chlorinated with chlorine gas under the catalysis of metals such as Fe and Sb.
Gas-Phase Method: Phthalic anhydride vapor is passed through a catalyst bed such as V₂O₅-TiO₂-WO₃ at 200–400℃ and reacts with chlorine gas.
Tetrachloro-o-xylene Oxidation Method
Using 3,4,5,6-tetrachloro-o-xylene as a raw material, chlorosulfonic acid is used as a solvent in a high-temperature reactor, and vanadium/titanium/tungsten oxide catalysts are used for gas-phase oxidation to obtain the product.
