Action of Metals other than Sodium on Halogen Compounds

The reaction is only applicable for the preparation of symmetrical compounds from mono-halogen derivatives. 

20 gms. (2 mols.) of iodobenzene are heated with 20 gms. (excess) of copper powder for 3 hours in a sealed tube (see p. 41) to 230°. The contents of the tube are extracted with ether, and the filtered extract fractionated, the ether being removed on a water bath and the fraction 245°—255° retained and recrystallised from alcohol. 

Reaction VIH. Action of certain finely divided Metals on Diazonium Compounds in Alcohol or Acetic Anhydride Solution.—This reaction is limited to the preparation of s-diaryl compounds. Copper, zinc, or iron powder may be used, but the former is, on the whole, the most satisfactory, especially when it has been freshly prepared according to Gattermann s 

The reaction proceeds smoothly in aqueous or absolute alcoholic, or in acetic anhydride solution. (B., 23, 1226 28, 2049.) Its exact course has not been worked out, but it may be formulated as follows — 

31 gms. (2 mols.) of aniline dissolved in 150 c.cs. of water and 40 gms. (slight excess) of concentrated sulphuric acid are diazotised in the usual way (see p. 372) with 23 gms. (2 mols.) of sodium nitrite in 10% solution. The diazonium solution is treated with 100 gms. of 98% alcohol and 50 gms. (excess) of copper powder (p. 508) are added while the whole is well stirred (see p. 39). A vigorous evolution of nitrogen occurs, and by the end of the reaction the temperature has risen to 30° or 40°. The stirring is continued for an hour, and then the mixture is steam distilled. The distillate at first consists chiefly of alcohol with small amounts of an oil insoluble in water. Small portions of it are tested from time to time by dilution with water. When a solid precipitate is thus obtained, the distillate is separately collected until no more solid comes over. The distillate is then heated to 71° to melt the solid diphenyl on cooling until solidification takes place, the still liquid portion is poured off. The product is almost pure, but may be recrystallised from alcohol. 

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