50 g. (75 mmol) of 5-methoxyacetylamino-2,4,6-triiodoisophthalic acid dichloride is dissolved in 200 ml. of dry DMF; 18 g. (97.3 mmol) of tributylamine is added thereto, the mixture is heated to 60° C., and, at this temperature, a solution of 7.5 g. (82.4 mmol) of 2,3-dihydroxypropylamine in 50 ml. of DMF is added dropwise thereto. The mixture is stirred for 2 hours at 60° C., then concentrated to 100 ml., and stirred into 1.2 l. of methylene chloride. The precipitate thus formed is vacuum-filtered, dried, refluxed twice with respectively 500 ml. of ethyl acetate, and filtered in the hot state. The evaporated filtrate yields 40.5 g. (56 mmol)=74.5% of theory of the desired product as a colorless solid.
