Phenols and aromatic alcohols: preparation and properties
Compounds in which the hydroxyl group is attached directly to a carbon of the benzene ring are phenols (C₆H₅OH — phenol, cresols, pyrocatechol); those with –OH on a carbon of a side chain are aromatic alcohols (C₆H₅–CH₂–OH, benzyl alcohol). Industrially phenol was made by hydrolyzing chlorobenzene with NaOH at high temperature and pressure (C₆H₅Cl + 2NaOH → C₆H₅ONa + NaCl + H₂O, then acid frees C₆H₅OH), and today mainly by the cumene process from benzene and propene (giving phenol and acetone). Phenol is a colourless crystalline solid with a characteristic smell, poorly soluble in cold water, it burns the skin and is toxic. The ring and –OH influence each other: phenol is a weak acid, so it reacts with alkali (C₆H₅OH + NaOH → C₆H₅ONa + H₂O) whereas an alcohol does not; with sodium it releases H₂. The ring is more reactive than benzene: bromine water gives a white precipitate of 2,4,6-tribromophenol (C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr), and nitric acid gives 2,4,6-trinitrophenol (picric acid). The qualitative test for phenol is a violet colour with FeCl₃. Uses: phenol–formaldehyde resins, medicines, dyes, antiseptics.
Table: phenol vs benzyl alcohol — formula, position of –OH, reaction with NaOH, reaction with FeCl₃. No experiments with phenol are done (the teacher only, with protective equipment).