Abstract: The reduction of the O-alkyl isomer content of 5-[N-(2-acetoxyethyl)acetoxyacetamido]-N,N'-bis(2,3-diacetoxypropyl)-2,4,6 -triiodoisophthalamide to thereby reduce and/or eliminate the production of impurities comparatively more difficult to remove during the purification of crude ioversol.

Abstract: An improved process for the preparation of N-acetyl-p-aminophenol. p-Aminophenol is acetylated in an aqueous medium to produce a crude aqueous reaction mixture and N-acetyl-p-aminophenol product is recovered by crystallization from an aqueous system comprising the reaction mixture. Crystals are separated from the crude mother liquor which contains residual N-acetyl-p-aminophenol and unreacted acetic acid. According to the improvement, residual N-acetyl-p-aminophenol and acetic acid are recovered from the crude mother liquor by liquid-liquid extraction with a water-immiscible organic solvent to produce an extract containing N-acetyl-p-aminophenol and acetic acid. The extract is distilled to strip off the solvent and acetic acid.

Abstract: The preparation of p-aminophenol by the catalytic hydrogenation of nitrobenzene in an acid reaction medium containing an aqueous isopropyl alcohol solution of trimethyldodecylammonium chloride leads to the formation of chloro- and isopropoxyaniline impurities. These end up in the by-product aniline. The substitution of dimethyldodecylamine sulfate for the quaternary salt eliminates these impurities without significant adverse effect on the yield, production rate or purity of the p-aminophenol.