1911] oji New Organic Compounds of Nitrogen. 157 



of artificial colouring matters known as aniline dyes depend largely, 

 though h\ no means exclusively, upon the process known to chemists 

 as " coupling." If an aromatic base which has been treated with 

 nitrous acid is added to one which has not been so diazotized, com- 

 bination usually takes place in such a manner that a derivative of 

 azobenzene is produced, and in the factory or laboratory coupling is 

 effected with aqueous solutions iuaintained at zero to avoid decom- 

 position of the diazo-group. A class of substances recently described 

 l)y Morgan and Micklethwait, however, make it possible to administer 

 the (liazo-complex in a solid form, thereby greatly facilitating a 

 demonstration of the coupling process ; on mixing a few decigrams 

 of toluene-j»-sulphonyl-^-phenylenediazoimide with the same quantity 

 of a-naphthylamine, adding a few c.c. of pyridine, and diluting the 

 solution with absolute alcohol, concentrated hydrochloric acid 

 develops an intense permanganate coloration. 



"We now arrive at the stage immediately preceding the organic 

 triazo-compounds. Just as hydrazme itself, when treated with 

 nitrous acid gives hydrazoic acid or azoimide, so phenylhydrazine 

 with nitrous acid gives phenylazoimide, 



CeHs-NH'NH^ + HNO2 = CeHs'Na +2H2O. 



Its production in this way gives the first indication of its properties, 

 for unlike auiline and phenylhydrazine, which are bases, phenyl- 

 azoimide is a neutral substance, resembling its haloid analogues, 

 chlorobenzene, bromobenzene, and iodobenzene. 



Although phenylazoimide was first brought to light by Griess 

 in 1866, the subject of triazo-chemistry lay dormant until the dis- 

 covery of hydrazoic acid by Curtius in 1890. Since that time the 

 province has been a flourishing one, and the number of triazo- 

 compounds which have been prepared and studied by Curtius and his 

 pupils constitute an imposing section of nitrogen chemistry. It is 

 principally with the acid azides, substances in which the triazo-group 

 plays the same part as chlorine in benzoyl chloride, that the in- 

 vestigations of Curtius have been concerned, and it is noteworthy 

 that some of the earliest syntheses of polypeptides were effected by 

 him simultaneously with Emil Fischer through the agency of these 

 compounds ; in the subsequent development of this Held, however, 

 the azide process gave way to the linking up by chlorides, as adopted 

 and elaborated by Fischer. The method by which Curtius prepared 

 his acid azides is really an adaptation of the change by which 

 hydrazoic acid itself is obtainable from hydrazine, namely, by the 

 action of nitrous acid upon the hydrazides of the respective acids, 

 and it may be stated in general terms that any derivative of azoimide 

 may be produced in this way provided the corresponding derivative 

 of hydrazine is available ; but this is the case only in certain classes 

 of compounds, and the preparation of aromatic azoimides is best 



