160 



Isomeric Change in Benzene Derivatives. 



[Dec. 1, 



to obtain the crystals free from the powder by frequently shaking up 

 the solid with water and decanting the supernatant liquor before the 

 light powder had had time to settle. 



X, 



3 : b-Dibromo-o-diazophenol (3 : b-dibromo-o-diazoqiiinone), 



Br 



The crystals, just mentioned, are the 3 : 5-dibromo-o-diazophenol in a 

 state of purity. They are long slender transparent prisms of a fine 

 orange colour, which explode when heated at 140'. 



0T894 gramme gave 0*2564 gramme AgBr. Br = 57*6. 



Two cryoscopic determinations of the molecular weight in benzene 

 solution gave the values 278*9 and 281*6. 



CjHoONoBro requires Br = 57*53 per cent., and a molecular weight 

 of 278~ 



The compound is very soluble in chloroform, benzene, ether and 

 glacial acetic acid, and in boiling alcohol. It is moderately soluble in 

 boiling water, and very slightly so in cold water or petroleum. Treat- 

 ment with hot water or alcohol decomposes it. It dissolves in con 

 cent-rated acids, forming a colourless solution, and is reprecipitated by 

 addition of water. The solution in acids couples with alkaline solutions 

 of /3-naphthol. The hydrochloride is obtained in nearly colourless 

 needles by passing dry hydrogen chloride into a dry ethereal solution. 

 This substance is without doubt the ortho-diazophenol, and not the 

 3 : 5-dibromo-^-diazophenol, which has been prepared by Silberstein 

 (loc. cit.), and which can be cn^stallised from hot water. 



In the account given by Hantzsch, of the experiments above re- 

 ferred to, it is stated that on adding sodium acetate to the solution of 

 a .y-tribromobenzenediazonium salt, the whole of the latter is gradually 

 converted into .s-tribromophenylnitrosamine, C ( ;HoBr 3 .xsH.NO, of 

 which analyses are given : it forms an amorphous yellow powder, 

 decomposing at 85°. By passing hydrogen chloride into the ethereal 

 solution, he obtained a hydrochloride of the nitrosamine, which is 

 immediately decomposed by water, a property possessed by the hydro- 

 chloride of the diazophenol. 



The amorphous yellow powder, obtained by the author, both by the 

 action of sodium hydrogen carbonate on the .s-tribromobenzenedia- 

 zonium salts, and mixed with crystals of the diazophenol when sodium 

 acetate is used, decomposes at 85 — 90° (compare Hantzsch, 85°). The 

 yellow substance appears to be similar to those obtained from s-tri- 

 chlorobenzenediazonium salts ; but determinations of the molecular 

 weight, indicate that only Wo benzeneazo-groups have condensed. In 

 this case, however, the yellow powder certainly contained some of the 

 diazophenol, as on passing hydrogen chloride into an ethereal solution 



