Structure of Simpler Organic Compounds. 149 



by means of which one group attached to the carbon of 

 a benzene nucleus may be replaced by another group. 

 Thus, for example, nitrobenzene, C 6 H 5 (NO 2 ), may be reduced 

 to aniline, C 6 H 5 (NH 2 ), the latter can be " diazotized " and 

 then treated with cuprous cyanide according to the Sand- 

 meyer reaction, and the cyanide or benzonitrile, C 6 H 5 (CN), 

 thus produced will yield on hydrolysis C 6 H 5 -COOH or 

 benzoic acid. As the diazo compounds are unstable, they are 

 not generally isolated when required for further operations ; 

 the amine salt in presence of excess of acid is treated with 

 the theoretical amount of amyl or sodium nitrite in cold 

 solution, and the solution of the diazonium salt is then 

 treated with the necessary reagent. Operations of the 

 above description are of importance in determining the 

 structure of many aromatic substances, as by such means 

 it is often possible to pass from a substance of unknown 

 to one of known composition. 



(d) Diazonium compounds can condense with a large 

 number of aromatic derivatives, and many of the substances 

 thus produced are valuable representatives of classes of 

 aniline dyes. Thus, for example, phenyldiazonium chloride 

 will condense with aniline 



C 6 H 5 .N 2 -C1 + C 6 H 6 .NH 2 = C 6 H 5 N,NH-C 6 H 5 + HC1 



to form diazoamino benzene; on warming this substance with 

 a small amount of aniline hydrochloride to 40, it under- 

 goes intramolecular change to form aminoazo benzene 

 C 6 H 6 -N 2 .NH C 6 H 5 = C 8 H,-N a .C 6 H 4 .NH 2 



The hydrochloride of this substance was formerly used as 

 a dye for silk under the name of " aniline yellow." 



The diazo compounds will also condense with amines 

 in which both the hydrogen groups are replaced by alkyl 

 radicles for example, with dimethyl aniline 



= C 6 H 5 -N 2 .C 6 H 4 -N(CH 3 ) 2 -HC1 



