N([O-])=O.[Na+].S(=O)(=O)(O)O.N[C:11]1[C:12]([I:27])=[C:13]([CH2:22][NH:23][C:24](=[O:26])[CH3:25])[C:14]([I:21])=[C:15]([C:19]=1[I:20])[C:16]([OH:18])=[O:17].[Cu][C:29]#[N:30].[C-]#N.[K+].N>O.C(O)(=O)C>[C:29]([C:11]1[C:12]([I:27])=[C:13]([CH2:22][NH:23][C:24](=[O:26])[CH3:25])[C:14]([I:21])=[C:15]([C:19]=1[I:20])[C:16]([OH:18])=[O:17])#[N:30]14 g of sodium nitrite is introduced under stirring into 170 ml of a concentrated sulfuric acid held at +5° C. The mixture is then maintained at +70° C. until solution has occurred, and then cooled to +5° C. After adding dropwise 84 ml of glacial acetic acid under cooling, 93.6 g of 5-amino-3-acetylaminomethyl-2,4,6-triiodobenzoic acid is added in incremental portions, maintaining the reaction temperature between 0° C. and +5° C. The reaction mixture is stirred for another 2 hours, poured on 800 g of ice, and, under cooling, introduced into a solution of 71 g of copper(I) cyanide and 133 g of potassium cyanide in a mixture of 1 1 of concentrated ammonia and 640 ml of water. After several hours of stirring in an ice bath, the precipitated ammonium salt is vacuum-filtered and dissolved in 4 l of water. After filtration over active carbon, the filtrate is adjusted to pH 6 with acetic acid, again extracted with active carbon, filtered, and the filtrate combined with excess concentrated hydrochloric acid. The thus-separated precipitate is dried at 50° C., thus obtaining 80.5 g (=85% theory) of 5-cyano-3-acetylaminomethyl-2,4,6-triiodobenzoic acid as a white powder, mp 271° C. (decomposition).
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