Reaction II.—Reduction under certain Conditions of Aromatic Ketones

Reaction II. Reduction under certain Conditions of Aromatic Ketones. 

If hydrochloric acid is added the reduction goes to the corresponding hydrocarbon e.g., from benzophenone s-tetraphenylethane is obtained. 

Reaction HI. Oxidation under certain Conditions of Lower Hydrocarbons. (B., 32, 432.)—In this reaction two molecules of a hydrocarbon are condensed, hydrogen being eliminated by the action of an oxidising agent. Two neutral oxidising agents, potassium persulphate and lead oxide, are especially useful in this type of reaction. The former is used in dilute aqueous solution, at a temperature of about 100° to obtain results with the latter much higher temperatures are necessary. The substance is mixed with the lead oxide and heated to over 250°, or it is distilled over heated lead oxide. The results obtained vary with the temperature and the amount of lead oxide used, e.g., fluorene can be oxidised to either 

It is to be noted that to obtain practicable yields this reaction must be confined to aromatic hydrocarbons. In the aliphatic series it only takes place, in a few cases, and then gives but a yield of the order of 1%. 

90 gms. potassium persulphate (1 mol.) are dissolved in a litre of water, and to this is added 60 gms. (2 mols.) of toluene. The mixture is heated on a water bath for 4 hours in a flask fitted with good agitation and a reflux condenser (see Eig. 38). The oily layer is then separated, dried over calcium chloride and fractionally distilled, the fraction 270°—280° consisting of dibenzyl and benzoic acid being separately collected. The earlier fractions consist of toluene and benzaldehyde. The dibenzyl fraction is dissolved in ether and the benzoic acid removed by shaking with dilute caustic soda solution. The ether is then removed on the water bath, and the residue recrystallised from dilute alcohol. 

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