# 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 which was used up to that date to prepare acetophenone.

Pressurized air is fed at 5 $bar$ and 130$°C$ 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 $h$. 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$°C$. 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.

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