Nitrophenol Explained

Nitrophenols are compounds of the formula HOC₆H_5-x(NO₂)_x. The conjugate bases are called nitrophenolates. Nitrophenols are more acidic than phenol itself.^[1]

Mono-nitrophenols

with the formula HOC₆H₄NO₂. Three isomeric nitrophenols exist:

• o-Nitrophenol (2-nitrophenol; OH and NO₂ groups are neighboring, a yellow solid.
• m-Nitrophenol (3-nitrophenol, CAS number: 554-84-7), a yellow solid (m.p. 97 °C) and precursor to the drug mesalazine (5-aminosalicylic acid). It can be prepared by nitration of aniline followed by replacement of the amino group via its diazonium derivative.^[2]
• p-Nitrophenol, yellow solid is a precursor to the rice herbicide fluorodifen, the pesticide parathion, and the human analgesic paracetamol (also known as acetaminophen).

The mononitrated phenols are often hydrogenated to the corresponding aminophenols that are also useful industrially.^[1]

Di- and trinitrophenols

• 2,4-Dinitrophenol (m.p. 83 °C) is a moderately strong acid (pK_a = 4.89).
• 2,4,6-Trinitrophenol is better known as picric acid, which has a well-developed chemistry.

Safety

Nitrophenols are poisonous. Occasionally, nitrophenols contaminate the soil near former explosives or fabric factories and military plants, and current research is aimed at remediation.^[3]

References

1. Encyclopedia: Gerald Booth. Nitro Compounds, Aromatic. Ullmann's Encyclopedia of Industrial Chemistry. 2007. Wiley-VCH. Weinheim. 10.1002/14356007.a17_411. 978-3527306732.
2. 10.15227/orgsyn.008.0080 . m-Nitrophenol . Organic Syntheses . 1928 . 8 . 80. R. H. F. Manske .
3. https://www.atsdr.cdc.gov/toxfaqs/tfacts50.pdf Fact sheet at atsdr.cdc.gov