Sulfuric Acid → 5-(Carbamoyl)-2,4,6-triiodoisophthalic acid

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Reaction Steps

100 g of 5-cyano-2,4,6-triiodoisophthalic acid is suspended in 400 ml of concentrated sulfuric acid and heated first under agitation for 30 minutes to 60° C., then for 2 hours to 95° C. The thus-produced, clear solution is then poured on 1.2 kg of ice and stirred for one hour in an ice bath. The thus-precipitated crude product is vacuum-filtered, dissolved under heating in 400 ml of ethanol, and the solution is combined with 70 ml of concentrated sodium hydroxide solution. After several hours of agitation in an ice bath, the thus-separated sodium salt is vacuum-filtered, washed with ethanol, and then dissolved in 200 ml of hot water. After treating the solution with active carbon, the filtrate is precipitated into 150 ml of semiconcentrated sulfuric acid. After several hours of stirring in an ice bath, the precipitate is vacuum-filtered, washed with a small amount of ice-cold water, and dried at 50° C., thus obtaining 84 g (=82% of theory) of 5-carbamoyl- 2,4,6-triiodoisophthalic acid, which conforms in its properties with the product of the alkaline saponification.

Provenance & Evidence