Color control & stability in acetaminophen

In a method of preparing N-acetyl-para-aminophenol (APAP) which comprises the steps of reacting acetic anhydride with a mixture of p-aminophenol and water, cooling the reaction mixture to precipitate crude APAP, filtering to remove excess acetic acid, neutralizing the wet APAP with a basic material, and agitating the resulting solution with carbon black, the improvement which comprises adding substoichiometric quantities of an acetylating agent to the crude APAP at any point after the formation of said crude APAP whereby the color bodies or their precursors in said crude APAP will be substantially converted to stable, colorless substances and substantially none of the APAP is converted to other compounds.

In a process of preparing an N-acyl-hydroxy aromatic amine which comprises the steps of contacting a hydroxy aromatic ketone with a hydroxylamine salt and a base to form the ketoxime of said ketone, and contacting said ketoxime with a Beckmann rearrangement catalyst to form a crude N-acyl-hydroxy aromatic amine containing color bodies or their precursors, the improvement which comprises the purification of said crude aromatic amine with substoichiometric quantities of an acetylating agent for a sufficient period of time to convert said color bodies or their precursors to substantially stable, colorless substances and substantially none of the N-acyl-hydroxy aromatic amine is converted to other chemical compounds.

In a method of preparing N-acetyl-para-aminophenol (APAP) which comprises the steps of reacting 4-hydroxyacetophenone with a hydroxylamine salt and a base to obtain 4-hydroxyacetophenone oxime and then subjecting the 4-hydroxyacetophenone oxime to a Beckmann rearrangement in the presence of a catalyst to form crude APAP containing color bodies or their precursors, the improvement which comprises the purification of said crude APAP by treating said crude APAP with substoichiometric quantities of an acetylating agent for a sufficient period of time to convert said color bodies or their precursors to substantially stable, colorless substances and substantially none of the APAP is converted to other chemical compounds.