5-Amino-2,4,6-triiodo-N-methylisophthalamic acid (228.0 g, 4 mole) was
added to stirred, heated dimethylacetamide (400 ml). When the temperature
reached 95°C, adipoyl chloride (27.5 g, 0.15 mole) was added all at once,
followed by an equal amount added slowly over a period of 15 min (a total of
55.0 g). After addition of the adipoyl chloride the solution was stirred at about
95°C for another 15 min, then poured into 2 L of hot water. As the above
mixture cooled to room temperature a gum separated. The mother liquor was
discarded and the gum was dissolved in water (2 L) with sufficient sodium
hydroxide to complete solution. The solution was acidified with hydrochloric
and acetic acids, treated with decolorizing charcoal and filtered. The filtrate
was then strongly acidified with hydrochloric acid, which caused the separation
of an apparently amorphous granular solid. This was filtered off, digested 0.5
h with hot ethanol (500 ml) collected, washed with ethanol and dried at
110°C. Yield of crude 5,5-(adipoyldiimino)-bis[2,4,6-triiodo-Nmethylisophthalamic acid].
The 5,5-(adipoyldiimino)-bis[2,4,6-triiodo-N-methylisophthalamic acid] was
precipitated a second and third time from its sodium salt solution. The third
precipitate was then dissolved in hot dimethylformamide (400 ml), and water
(1.5 L) was slowly added. The mixture was digested and the hot mixture
filtered, yielding a crystalline product which, after drying at 110°C, weighed
126.0 g (neutral equivalent, 724). This product was dissolved in dilute sodium
hydroxide solution (1 L) and the solution was acidified (pH 5) and filtered into
a hot stirred solution of hydrochloric acid (25 ml of concentrated acid in 75 ml
water). The mixture was chilled and the solid collected, washed with water
and dried at 110°C. Yield of 5,5-(adipoyldiimino)-bis[2,4,6-triiodo-Nmethylisophthalamic acid] 114.0 g (45%). Melting point, 302°C (corrected),
with decomposition.
