192 REPORT— 1902. 



but the test is not very decisive since the metallic zso-diazo-oxides them- 

 selves couple with y8-naphthol dissolved in alkali hydroxide, providing 

 that the solution is not too alkaline. 



It was next found that potassium benzenediazo-oxide exists in two 

 modifications, the iso form pi'eviously mentioned, and the normal form 

 which coupled with the phenols much more readily than its isomeride. 

 This type of isomerism obtains generally amongst the metallic diazo- 

 oxides, but the presence of negative substituents in the aromaticynucleus 

 greatly diminishes the stability of the normal modification. On this 

 account it is usually very difficult to obtain both isoraerides in a state of 

 purity. 



Isomeric salts have, however, been prepared from diazobenzene- 

 sulphonic acid ; the normal basic sodium salt, NaOISr2C5H4S03]S'a, 4H2O, 

 is obtained by working with cooled solutions, whilst the wo-salt, which 

 separates in anhydrous crystals, is produced by heating a solution of its 

 isomeride ; they are both strongly alkaline and are distinguished by their 

 behaviour towards y8-naphthol, the former salt readily coupling whilst the 

 latter exhibits this property to a very slight extent. The corresponding 

 potassium compounds have been isolated, and similar pairs of isomeric 

 alkali salts have also been prepared from p-bromodiazobenzene-o-sul- 

 phonic acid.^ 



Diazo- and Isodiazo-oxides. — When the isomeric diazo-oxides were 

 first investigated there existed a tendency to exaggerate the differences 

 between the isomerides, and they were originally supposed to dififer 

 essentially in the following respects : — 



(i) Capacity for coupling with phenols or ethyl aceto-acetate and 

 similarly constituted compounds. 



(ii) Behaviour towards alkylating, reducing, and oxidising agents, 

 (iii) Interaction with benzoyl chloride and alkali hydroxides. 



Production of Azo-derivatives. — The normal diazo-oxides exhibit the 

 greater tendency to combine with the phenols, but in the case of both 

 isomerides the rate of formation of hydroxyazo-compounds is largely 

 dependent on the nature of the aromatic radicle attached to the diazo- 

 group, and the free isomeric diazo-hydroxides couple with phenols even 

 more readily than their potassium derivatives.'^ 



It was at first supposed that the metallic isodiazo-oxides did not condense 

 with ethyl aceto-acetate,^ difiering essentially in this respect from the normal 

 derivatives which had long been known to furnish condensation products 

 with the ester,-* but Billow subsequently sliowed that the isodiazo- compounds 

 yield mixed aliphatic-aromatic hydrazones or azo-derivatives.'^ This cor- 

 rection, although suggesting the structural identity of the normal and 

 ^sodiazo-oxides, does not assist in deciding between the two formulas 

 B.N : NOH and R.NH.NO, owing to the uncertainty which still exists 

 with regard to the constitution of the aromatic and mixed condensation 

 products, these substances being regarded by some authorities as azo- 

 derivatives, and by others as hydrazones. 



' Hantzsch, Bfir., 1895, 28, 2002 ; 1900, 33, 2158 ; and Gerilowski, ibid., 2317. 

 - Bamberger, Ber., 1898, 28, 4i4. ' Schraube and Schmidt, loc. cit. 



* Japp and Klingemann, ^er., 1887, 20, 3398; Annalen, 247,190; and Claisen 

 and Beyer, JBer., 1888, 21, 1697. 



£er., 1898, 31, 3122; 1899, 32, 197 



