204 REPORT— 1902. 



The amount of coloured s^/w-compouncl present depends largely on 

 the nature of the acid radicle X. 



The diazonium chlorides, and nearly all the bromides, are colourless 

 and corapai'atively stable. The iodides are all coloured, and very explosive, 

 the thiocyanates are somewhat less coloured than the iodides, and are 

 intermediate in stability between these and the bromides. 



The influence of substituent radicles in the aromatic radicle R is 

 scarcely noticeable with the diazonium chlorides ; but with the other salts 

 it is found that the stability is increased by the introduction of methyl 

 and methoxy groups, and diminished by that of acidic radicles.^ At low 

 temperatures even the very explosive diazonium salts become stable, and it 

 is noticed that, on cooling, their colour is perceptibly diminished.^ 



The Residual Affinity of Diazonium Salts.'^ — The characteristic fission 

 of diazonium salts is very probably due to the preliminary addition of a 

 reagent HE,, and the subsequent elimination of the hydride of the acid 

 radicle with the formation of an unstable s^/^i-diazo-compound, 



' N : N + HCl -> ^=-^, 



This hypothesis affords a general explanation of the Sandmeyer re- 

 action, and also of the interaction between diazonium salts and water 

 or alcohol.' 



R OCHs R OC2H, 



N : N+ I " -> N : N -^ R.OC2H5 + N2 + HCI 



CI ^ CI H 



R H R H 



N ; N+ I ->. N ; N ^ R.H+N2+HCI+C2H4O. 



CI OC2H5 ci oc^H^.H 



The cuprous salts of the Sandmeyer reaction combine with syn- 

 diazo-compounds to form coloured double salts of the azo-type, and, in this 

 way, induce the conversion of the diazonium salt into the pseudo-diazoniura 

 or syn-iorm. which subsequently decomposes in the characteristic manner. 



The diazonium perhalides are substances analogous with the periodides 

 of potassium, caesium, and the quaternary ammonium bases. The halogen 

 atoms are certainly not attached to both nitrogen atoms, since the com- 

 pound CrtH-,]Sr2ClBrI is produced either from C6H5N.,C1 and IBr or 

 from CeH.N.^Br + ICl.-' 



Hyclrolytic Dissociation of the Alkali Diazo-oxides. — It has already been 

 seen that the metallic syn- and mi<i-diazo-oxides are much alike in their 

 general chemical behaviour, providing that their reactions are studied in 

 fairly alkaline solutions. The s^»-isomerides, however, exhibit anomalous 

 properties in dilute neutral solution, and this phenomenon has been found, 

 by determinations of the electrical conductivity,'' to be due to the 



» Jier., 1900, 33, 2179. = Ber., 1901, .34, 4166. 



= £er., 1897, 30, 2548; 1898, 31, 2053. * Ber., 1900, 33, 2517. 



* Ber., 189D, 28, 2754. . « Ber., 1898, 31, 1612. 



