Sulfuric Acid → 3-Cyano-2,4,6-triiodobenzoic acid

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Reaction Conditions

Reaction Steps

20.6 g. of 3-amino-2,4,6-triiodobenzoic acid is suspended in 220 ml. of water. After the dropwise addition of 24 ml. of a 30% aqueous sodium nitrite solution at 0° C., the pH value is brought down to 2 by adding dilute sulfuric acid. The batch is then stirred for one hour in an ice bath. By the gradual, dropwise addition of dilute sodium hydroxide solution, the batch is raised to pH 4.5, and the solution is allowed to stand under ice cooling. In the meantime, a solution of 20 g. of copper(I) chloride and 34 g. of potassium cyanide in 160 ml. of water has been prepared, warmed to 30° C., and the diazotization solution is added thereto all at once, under the occurrence of strong frothing. The mixture is stirred for another 15 minutes at 30° C. and then the copper salts are separated by acidifying the reaction solution to pH 3 with concentrated hydrochloric acid. The filtrate is brought to pH 0.5- 1 by the further addition of concentrated hydrochloric acid, and the precipitate, after several hours of agitation in an ice bath, is vacuum-filtered and washed with water. The compound, moist from vacuum-filtering, is suspended in 50 ml. of water, dissolved by adding dilute sodium hydroxide solution, and the solution is treated by stirring with activated carbon and filtered to a clear state. By adding drops of concentrated hydrochloric acid, the solution is brought to pH 0.5-1 and then stirred for several hours in an ice bath; the precipitate is vacuum-filtered. After washing with acetone-containing water and drying at 50° C., 16 g. (76% of theory) of 3-cyano-2,4,6-triiodobenzoic acid is obtained as a white powder, m.p. 238°-240° C. (decomposition).

Provenance & Evidence