n indane, tetralin or phenyl alcohol is made by a heterogeneous, fast, exothermic Friedel Craft reaction and the reaction mixture is cooled to a temperature at which substantial by-product formation is avoided by continuously utilising the heat of reaction to boil solvent from the reaction mixture. The reaction mixture is generally maintained below atmospheric pressure, typically 20 to 100 mm Hg. The process is of particular value for the production of aryl alcohols by reacting an indane or tetralin with ethylene oxide or propylene oxide.