4Nitrophenol

4-Nitrophenol, commonly called p-nitrophenol, is an aromatic organic compound with the formula C6H5NO3. It is one of the two principal nitrophenol isomers, the other being 2-nitrophenol. The molecule consists of a phenol ring with a nitro group para to the hydroxyl group.

4-Nitrophenol appears as a colorless to pale yellow crystalline solid. It melts at about 114–116°C and decomposes at higher temperatures. It is moderately soluble in water and more soluble in many organic solvents such as ethanol and acetone. In basic solution, it forms the yellow p-nitrophenolate ion, which has strong absorption near 405 nm and is used in colorimetric applications.

Preparation typically involves the nitration of phenol with nitric acid; under standard nitration conditions the para isomer is favored, though some ortho isomer forms and must be separated.

Reactions: It can be reduced to 4-aminophenol, a key intermediate for the synthesis of paracetamol (acetaminophen). It can also undergo further substitution and be used as a starting material for dyes and pharmaceutical intermediates. Its chromogenic properties also support use as a substrate in enzyme assays and analytical chemistry.

Safety and environment: 4-Nitrophenol is toxic and irritating to skin, eyes, and the respiratory tract. It should be handled with appropriate PPE and disposed of as hazardous waste. It can be harmful to aquatic life and should be released to the environment only under proper controls.