4-Aminophenol is a building block used in organic chemistry. Prominently, it is the final intermediate in the industrial synthesis of paracetamol. Treating 4-aminophenol with acetic anhydride gives paracetamol:

• Ellis, Frank (2002). Paracetamol: a curriculum resource. Cambridge: Royal Society of Chemistry. ISBN 0-85404-375-6.
• Anthony S. Travis (2007). “Manufacture and uses of the anilines: A vast array of processes and products”. In Zvi Rappoport (ed.). The chemistry of Anilines Part 1. Wiley. p. 764. ISBN 978-0-470-87171-3.
• Elmar Friderichs; Thomas Christoph; Helmut Buschmann. “Analgesics and Antipyretics”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a02_269.pub2.

4-Aminophenol (or para-aminophenol or p-aminophenol) is an organic compound with the formula H₂NC₆H₄OH. Typically available as a white powder, it is commonly used as a developer for black-and-white film, marketed under the name Rodinal (the trade name of a black and white developing agent produced originally by the German company Agfa based on the chemical 4-aminophenol. Rodinal is a popular high acutance black and white developer and is used at different dilutions for development in rotary machines, by agitation, as well as for stand development. It was patented on 27 January 1891, making it the oldest film developer which is still commercially available. Novel at the time of its invention was that it is delivered as a liquid concentrate and not as a powder. During the division of Germany the original manufacturer Agfa was split, becoming the ORWO company in East Germany, where Rodinal was sold under the name ORWO R09. After the insolvency of Agfa in 2004, production was taken over by the re-formed ADOX, which also purchased the trademark rights in the name in Europe (excluding France) and continues to sell the product under this name.)

• CRC Handbook of Chemistry and Physics 65th Ed.
• “Rodinal” (PDF). Afga. Retrieved 17 March 2013.

Reflecting its slightly hydrophilic character, the white powder is moderately soluble in alcohols and can be recrystallized from hot water. In the presence of a base, it oxidizes readily. The methylated derivatives N-methylaminophenol and N,N-dimethylaminophenol are of commercial value.

The compound is one of three isomeric aminophenols, the other two being 2-aminophenol and 3-aminophenol.

Preparation of 4-Aminophenol

From phenol

It is produced from phenol by nitration followed by reduction with iron. Alternatively, the partial hydrogenation of nitrobenzene affords phenylhydroxylamine, which rearranges primarily to 4-aminophenol (Bamberger rearrangement).

C₆H₅NO₂ + 2 H₂ → C₆H₅NHOH + H₂OC₆H₅NHOH → HOC₆H₄NH₂

• Mitchell, S.C. & Waring, R.H. “Aminophenols.” In Ullmann’s Encyclopedia of Industrial Chemistry; 2002 Wiley-VCH, doi:10.1002/14356007.a02_099

From nitrobenzene

It can be produced from nitrobenzene by electrolytic conversion to phenylhydroxylamine, which spontaneously rearranges to 4-aminophenol.

• Polat, K.; Aksu, M.L.; Pekel, A.T. (2002), “Electroreduction of nitrobenzene to p-aminophenol using voltammetric and semipilot scale preparative electrolysis techniques”, Journal of Applied Electrochemistry, Kluwer Academic Publishers, 32 (2): 217–223, doi:10.1023/A:1014725116051, S2CID 54499902

From 4-nitrophenol

4-nitrophenol can be reduced through a variety of methods, to yield 4-aminophenol. One method involves hydrogenation over a Raney Nickel catalyst. A second method involves selective reduction of the nitro group by Tin(II) Chloride in anhydrous ethanol or ethyl ethanoate. 

• US2998450A, Godfrey, Wilbert & De, Angelis John, “Process of preparing nu-acetyl-p-amino phenol”, issued 1961-08-29
• Bellamy, F. D.; Ou, K. (1984-01-01). “Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous medium”. Tetrahedron Letters. 25 (8): 839–842. doi:10.1016/S0040-4039(01)80041-1. ISSN 0040-4039.

It is a precursor to:

amodiaquine, mesalazine, AM404, parapropamol, B-86810 & B-87836 (c.f. WO 2001042204).

4-Aminophenol converts readily to the diazonium salt.

• F. B. Dains, Floyd Eberly (1935). “p-Iodophenol”. Organic Syntheses. 15: 39. doi:10.15227/orgsyn.015.0039