5-Amino-2,4,6-triiodo-isophtalic acid (30 g, 0.054 mol), thionyl chloride (8.2 ml, 0.113 mol) and pyridine (0.2 ml) in 1 ,2 dichloroethane (20 ml) were heated to 70 ℃. A portion of thionyl chloride (15.2 ml, 0.21 mol) was added dropwise during 2 h, and the mixture was heated to 85 ℃ for 6 h. After cooling the reaction mixture to room temperature, it was poured into 300 g of ice-water. The yellow precipitate was filtered off, sucked dry and then washed with water until pH=5. The filter cake was then dried in a vacuum oven for 3 hrs. A light yellow powder was obtained as 5-Amino-2,4,6-triiodisophthaloyl acid dichloride.
