Diazonium perbromides

For the preparation of chlorides or bromides, the diazonium salt is decomposed with a solution of cuprous chloride or bromide in the corresponding halogen acid (Sandmeyer reaction). It is possible to prepare the aryl bromide from the diazonium chloride or sulfate. A variation Involves the use of copper powder and a mineral acid for the decomposition step (Gattermann reaction). Both procedures are illustrated by the syntheses of the isomeric bromotoluenes and chlorotoluenes. The usual conditions of the Sandmeyer reaction fail in the preparation of the chloro- and bromo-phenanthrenes. However, these compounds can be successfully obtained by the interaction of the diazonium compound with mercuric and potassium halides (Schwechten procedure). Another procedure for formation of aryl bromides involves treatment of the amine hydrobromide with nitrogen trioxide in the presence of excess 40% hydro-bromic acid. The Intermediate diazonium perbromide is then decomposed by heat. ... 

Diazonium bromides and bromine in hydrobromic acid give diazonium perbromides that are sparingly soluble in water. In the presence of water or when... 

Phenyl azide from benzenediazonium perbromide and ammonia 262 A 21 % solution (15 ml) of ammonia is covered with a layer of ether (10 ml) and to it is added, with ice-cooling and good stirring, the diazonium perbromide (4.05 g) in small portions a surface reaction between the perbromide and the ammonia leads to immediate and quantitative production of phenyl azide which is taken up by the ether phase. Then the ether is evaporated and the two-phase residue is subjected to steam-distillation. The distillate, which contains ammonia, is acidified with dilute sulfuric acid, and the phenyl azide is extracted in ether and then distilled in a high vacuum into a receiver cooled in solid carbon dioxide. The yield is 55 % (0.775 g). 

The diazonium perbromide is prepared as described in Gattermann and Wieland s book.lf... 

The diazonium salts precursors can be aniline, o- and p-toluidine, o-and p-anisidine, o- and p-phenetidine. or 3-naphthy]amine. The resulting formazans are crystalline and inlensel> colored. They are soluble in organic solvents, giving a red-violet coloration that darkens to blue. Dehydrogeneration gives the corresponding tetrazolium salts, which are isolated as perbromides (Scheme 51. Table X-13). 

The diazonium salt on the filter is dissolved in ice-water and is used for the preparation of phenyldiazonium perbromide and phenyl azide (see below). 

Phenyldiazonium Perbromide.—To a fresh ice-cold solution of one of the solid diazonium salts, prepared as described above, or to the diazo-solution from 2 g. of aniline, there is added the solution of 1-5 c.c. of bromine in 15 c.c. of potassium bromide solution (25 per cent), with ice cooling, until precipitation of dark-coloured oil ceases. The aqueous solution is then decanted when the residual perbromide is washed a few times with ice-water it crystallises. 

The mechanism of the reaction with ammonia is as follows. The perbromide bromine is converted into hypobromite and at the same time the diazonium salt undergoes rearrangement to syre-diazohydroxide, which immediately couples with NHS to give phenyltriazene ( diazo-benzeneamide ). The latter is then dehydrogenated by the hypobromite yielding phenyl azide (Dimroth) ... 

Azido-3,5-dinitro-l,4-dime thylbenzene, pitlts (from dii aic), mp 71—73° mod soi in benz acet ac si sol in ale v si sol in henzine prepd from 3,5 dinitro p-xylol-diazonium-2-perbromide thru reaction with aq NH3 on heating to 105—30°, it forms 5,6-Dinitroso-2-nitro-I,4-dimethylbenzene(qv). 

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