Oxidation of Methylene Groups to Carbonyl Groups
Oxidation of Methylene Groups to Carbonyl Groups: Industrial Application
Of technical interest is the synthesis of acetophenone from ethylbenzene by oxidation with atmosperic oxygen. In 1949, this method replaced the Friedel-Crafts reaction which was used up to that date to prepare acetophenone.
Pressurized air is fed at 5 and 130 into a reaction vessel containing ethylbenzene and manganese or cobalt salts of oil-soluble fatty or naphthalene acids as catalysts. The reaction mixture is transferred to a second vessel at which time pressurized air is introduced again. The oxidation is finished after 1.5 . During this time, 16% of ethylbenzene is converted to acetophenone in the first vessel and 10% in the second. Since at low conversion rates 1-phenylethanol and at higher rates benzoic acid are formed as the main side products, the reaction is stopped at this point. After extracting benzoic acid with a 10% solution of sodium hydroxide, the reaction mixture is distilled. Ethylbenzene and catalyst are re-used for oxidation. The mixture of acetophenone (68%) and 1-phenylethanol (32%) is catalytically dehydrogenated at 200. After conversion of the alcohol is completed, acetophenone is distilled in a yield of 85%, based on converted ethylbenzene.
Today, work-up of the side products from the Hock phenol synthesis provides sufficient acetophenone to cover the demand and eliminate the need for a specific synthesis of the ketone.