Cumene process (industrial): Cumene (isopropylbenzene) oxidised by air to cumene hydroperoxide, then acid-catalysed decomposition gives phenol + acetone. Most economical — both products are valuable. From diazonium salt: ArNH2 + NaNO2/HCl (273 K) -> ArN2+Cl-; ArN2+ + H2O (warm) -> ArOH + N2 + HCl. Reliable lab method. Dow's process: C6H5Cl + 2NaOH (623 K, 300 atm) -> C6H5ONa -> C6H5OH (acidify). Harsh conditions needed because aryl C-Cl bond is strong. From sodium benzenesulphonate: C6H5SO3Na + NaOH (fuse, 573 K) -> C6H5ONa -> C6H5OH. Classical method, less used now.