Mallinckrodt, Inc.

Edward L Derrenbacker

Thomas J Dunn

William R Clingan

An improved process for the recovery and extractive purification of p-aminophenol is disclosed. The process involves contacting an aqueous feed solution prepared by catalytic reduction of nitrobenzene in acid medium and containing 4,4-diaminodiphenyl ether, aniline and other minor amine by-products with a base to adjust the pH of the solution to 4.0-5.0, and then extracting the resulting aqueous feed solution with a mixture of aniline and toluene to selectively dissolve 4,4'-diaminodiphenyl ether in the aniline-toluene mixture and to produce an aqueous phase containing principally p-aminophenol and an organic aniline-toluene phase cotaining p-aminophenol, 4,4'-diaminodiphenyl ether and other amine by-products. The ratio of aniline to toluene is within the range between approximately 4 parts by volume aniline to 1 part by volume toluene and approximately 1 part by volume aniline to 4 parts by volume toluene, preferably a ratio of 1:1. After separation of the aqueous phase from the organic phase, the p-aminophenol of improved purity is recovered from the aqueous phase. Further efficiency in the overall yield of p-aminophenol is achieved by back-extracting the organic phase with a basic solution of potassium or sodium hydroxide to produce an aqueous layer containing the basic solution and substantially all of the p-aminophenol formerly contained in the organic phase and then recycling the aqueous layer for use as a portion of the base used to adjust the pH of the original aqueous feed solution to the range of 4.0 to 5.0. Another feature disclosed is the fractional countercurrent extraction of the original aqueous feed solution having a pH of 4.0 to 5.0 with an aniline-toluene mixture and an ammonium sulfate solution, aniline sulfate or sulfuric acid to selectively dissolve 4,4'-di-aminodiphenyl ether in the aniline-toluene mixture and to produce an aqueous phase from which a greater yield of p-aminophenol of improved purity may be obtained.

Process for the purification of p-aminophenol

An improved process for preparing p-aminophenol by the catalytic hydrogenation of nitrobenzene in an aqueous acidic reaction medium containing a dimethylalkylamine oxide whereby the hydrogenation rate is increased and the selectivity of the reaction for p-aminophenol is improved.

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St. Louis, MO, United States of America

Edward L Derrenbacker