4-Aminophenol – what a molecule!
This is a humble organic compound with the formula H2NC6H4OH, but don’t let its unassuming structure fool you. This is not just any crystalline powder; this is a chemical that moonlights as a pharmaceutical ingredient, a hair dye precursor, and—wait for it—a black-and-white film developer. If molecules had résumés, 4-Aminophenol’s would read like someone who’s worked as a barista, a stunt double, and an astrophysicist.
The Overachiever of Chemistry
First off, let’s talk about its starring role in the production of paracetamol (acetaminophen). Yes, the stuff you pop for headaches and fevers owes its existence to 4-Aminophenol. But here’s the kicker: this molecule is toxic to aquatic life, can cause kidney damage with prolonged exposure, and smells like rotten eggs. Imagine being both the hero and the villain in your own story—Shakespeare would be proud.
Aesthetic Chaos
As if saving humanity from migraines wasn’t enough, 4-Aminophenol decided it wanted to dabble in beauty. It’s a precursor for oxidative hair dyes, which means it helps people go from “meh” to “wow” in one salon appointment. But don’t get too attached—it’s also sensitive to air and light, turning brown faster than your avocado toast. Basically, it’s the unreliable friend who shows up late to brunch but still insists on splitting the bill evenly.
The Film Noir Connection
Now let’s get cinematic: 4-Aminophenol was once marketed under the name Rodinal as a developer for black-and-white film. Picture this—photographers in darkrooms, bathed in red light, whispering sweet nothings to trays of chemicals. And there it is: 4-Aminophenol, transforming blank film into moody masterpieces. It’s like the brooding artist of molecules—always slightly hydrophilic but never fully dissolving in water.
Health Hazards? Sure!
Of course, no chemical worth its salt escapes without a dark side. Dermal sensitization? Check. Central nervous system depression? Double check. Kidney injury? Oh, absolutely. And let’s not forget its ability to cause methemoglobinemia—a condition where your blood decides it doesn’t want to carry oxygen anymore because it’s too cool for school.
Questions for another day
-Who first thought, “Let’s take this slightly toxic molecule and make medicine out of it”? Genius or lunatic?
-Why does it smell like rotten eggs? Is that just its way of saying “Don’t mess with me”?
-Can we please talk about how it turns violet when exposed to light? Is this molecule auditioning for a role in Willy Wonka?
4-Aminophenol is the chemical equivalent of that one friend who has five side hustles and somehow still finds time to ruin brunch plans with their drama. Whether it’s curing headaches or developing film noir masterpieces, this molecule is chaotic good—or maybe just chaotic neutral—with a flair for theatrics.
Other Notes (Wikipedia)
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
