Reaction LXI.—Reduction of Diazonium Compounds to the corresponding Hydrocarbon

) When a diazonium compound is boiled with an alcohol, oxidation of the latter to the corresponding aldehyde and simultaneous replacement of the diazonium group by hydrogen occurs. 

The method is much used to remove the amino group from an aromatic nucleus, and has had some important theoretical applications. 

50 gms. (1 mol.) of finely powdered s-tribromoaniline (0. S., XIII., 96) are treated with 300 e.es. of absolute alcohol and 75 e.es. of benzene added to insure complete solution. 20 e.es. (excess) of cone, sulphuric acid are run in should a precipitate form, it is redissolved by the addition of more benzene. 20 gms. (excess) of pure finely powdered sodium nitrite are added to the hot liquid as rapidly as possible without the reaction becoming too violent, and the whole heated until effervescence ceases. After standing over-night the precipitate is filtered, washed at the pump with hot water until the washings give no precipitate with barium chloride, dried on a porous plate and recrystallised from absolute alcohol. 

30 gms. (1 mol.) of benzidine are added to 60 e.es. cone, hydrochloric acid and 400 e.es. water. The whole is heated until the benzidine is dissolved. After cooling it is diazotised with 23 gms. (2 mols.) of sodium nitrite (see p. 380). To the ice-cold tetrazonium solution are added 350 e.es. of commercial hypophosphorous acid (D. 1 15). After standing for several days in an ice chest, until no more solid separates, the diphenyl is 

Hypophosphorous acid may be prepared by digesting 150 gms. finely powdered calcium hypophosphite with 45 c.cs. of cone, sulphuric acid, and 500 c.cs. water for 1 hour at 80°, and removing the calcium sulphate by filtration. 

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