Action of Dehydrating Agents on certain Ketones

Reaction IV. (6) Action of Dehydrating Agents on certain Ketones. 

Besides its dehydrating action, the purely condensing capabilities of sulphuric acid should not be overlooked. Thus methyl acetylene condenses in the presence of sulphuric acid to mesitylene. (B., 29, 958, 2884.) 

This reaction is similar to the polymerisation of acetylene to benzene by the action of heat. 

400 gms. of clean dry sand are placed in a 2-litre retort connected with a condenser. 250 gms. (3 mols.) of acetone are added, and then a cooled mixture of 560 gms. of concentrated sulphuric acid and 150 gms. of water is run in, in a slow continuous stream, the retort being meantime cooled in cold water. After 24 hours standing, the mixture is slowly distilled, directly or in steam. When oily drops appear in the neck of the retort, the receiver is changed, and the distillate collected until only very small quantities of the oil appear. The colour of the liquid (if directly distilled) changes to deep brown, and finally to black, sulphur dioxide is evolved, and the mass froths up considerably. The upper yellowish layer of the distillate is separated from the lower aqueous layer, washed with caustic soda and water, and dehydrated over calcium chloride. It is then fractionated, the fraction 100°—200° being redistilled four times over thin slices of metallic sodium, when about two-thirds of it is obtained as pure mesitylene coming over at 161°—166°. 

Acetophenone condenses in a similar manner if it is heated with phosphorus pentoxide, or better if saturated with dry hydrogen chloride at ordinary temperatures. s-Triphenylbenzene is deposited after standing 

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