pnitrophenol

p-nitrophenol, also known as 4-nitrophenol, is an aromatic organic compound consisting of a benzene ring bearing a nitro group at the para position relative to a hydroxyl group. Its molecular formula is C6H5NO3 and its molar mass is 139.11 g/mol. It typically appears as colorless to pale yellow crystals and is sparingly soluble in water, with greater solubility in organic solvents.

Production and occurrence: p-nitrophenol is mainly produced by the nitration of phenol using mixed acid systems, which yields a mixture of ortho- and para-nitrophenol that is subsequently separated and purified. It can also be derived in steps from other nitroaromatic precursors. In commercial contexts, the para isomer is isolated for use in various industrial applications.

Uses and applications: The compound serves as an intermediate in the synthesis of dyes, agrochemicals, and pharmaceuticals. In laboratory settings, p-nitrophenol and its esters are widely used as substrates in enzyme assays, providing a colorimetric readout when hydrolyzed or deprotected. It also acts as a pH indicator in some analytical procedures, shifting from colorless to yellow as the solution becomes more basic, with a transition near neutral pH.

Safety and environmental impact: p-nitrophenol is irritating to skin and eyes and can be toxic if inhaled or ingested. It should be handled with appropriate protective equipment and disposed of according to local regulations. Environmentally, it can be harmful to aquatic life and may persist under certain conditions, though it may degrade through photolysis and microbial action in the environment.