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 Preparation of Tetraiodophthalic anhydride
  • Preparation of Tetraiodophthalic anhydride
  • Tetraiodo (CAS NO.: ), with other names as Phthalic anhydride, tetraiodo-, could be produced through the following synthetic routes.

    Preparation of Tetraiodophthalic anhydride

    In a 3-l. three-necked flask with ground-glass joints are placed 148 g. (1.0 mole) of phthalic anhydride, 324 g. (60% of the total of 2.12 moles to be added) of iodine, and 600 ml. of 60% fuming sulfuric acid. The flask, fitted with an air condenser 90–100 cm. in length, is arranged for ing by a water bath. A tube leads from the condenser to a gas trap.

    The temperature of the water bath is raised cautiously to 45–50°, at which point the reaction begins. Heating is continued until visible reaction has almost completely stopped. During this time, the temperature has been raised gradually to 65°. The flask is then cooled by flooding the bath with ice water, and a second portion, 162 g. (30% of the total), of iodine is added. The flask is heated again at 65° until the reaction ceases. After cooling as before, the last portion, 54 g. (10% of the total), of iodine is added.

    When reaction at 65° has ceased and the flask has been cooled, the condenser is removed, and the flask is arranged for heating on an oil bath in a well-ventilated area. The temperature of the bath is raised to 175° and maintained at 170–180° until the evolution of sulfur trioxide and iodine fumes has slowed considerably (about 2 hours at 170°). The flask is allowed to cool to about 60° before the contents are poured into a beaker, which is allowed to stand overnight at room temperature.

    The solid is filtered by suction on a glass filter cloth and is washed with two 100-ml. portions of concentrated sulfuric acid and then with three 200-ml. portions of water. The light-yellow crystalline material is then transferred to a 3-l. beaker where it is stirred for 30 minutes with a solution of 20 g. of sodium bisulfite in 1.5 l. of water to remove the last traces of iodine. The heavy solid is allowed to settle to the bottom of the beaker, and the bisulfite solution is poured off. The crystals are washed with three 1-l. portions of water, each portion being decanted as before, and then are transferred to a funnel. The product is washed with an additional 1-l. portion of water and two 200-ml. portions of acetone and dried in an oven at 60°. The product amounts to 520–535 g. (80–82% based on the phthalic anhydride) and melts at 327–328°.


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