Sodium Hydroxide → N,N'-Bis(1,3-dihydroxy-2-propyl)-5-[N-(2-hydroxy-3-methoxypropyl)acetamido]-2,4,6-triiodoisophthalamide

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5-Acetamido-N,N'-bis(1,3-dihydroxy-2-propyl)-2,4,6-triiodoisophthalamide (1036 g, 1.39 mol) was slurried in a mixture of propylene glycol (4170 ml) and methanol (4170 ml). After adding 18.25 M sodium hydroxide (114 ml, 2.08 mol), the mixture was heated at about 50°. When all or nearly all of the starting material was dissolved, the excess of methanol was evaporated in vacuo. Thereafter 2-hydroxy-3-methoxypropyl chloride (259 g, 2.08 mol) was added. The reaction mixture was heated at 50° for 44 hours and then stored at room temperature for 44 hours. Ater neutralization with concentrated hydrochloric acid, the reaction mixture was evaporated in vacuo. The residue was dissolved in methanol (3500 ml) and treated with a mixture of Dowex anion exchange resin 1×4 (2.87 kg) and Amberlite cation exchange resin (1.2 kg). The ion exchange resin was filtered off and washed with 80% aqueous methanol. The filtrate was evaporated in vacuo to dryness and the residue dissolved in isopropyl alcohol (5 1) at 80°. The product was precipitated by cooling to 13.5° and collected on a filter. Further purification was performed by recrystallization from isopropyl alcohol (4 1).

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