l68 OXIDATION PRODITCTS OF DIANISIDINE. 



dianisidine. was reduced by SnCia, and the tin removed from the 

 diluted solution by HgS. On concentrating somewhat, adding 

 ammonia, and cooling, the reduction product came out in hair-like 

 needles and glistening scales melting at 133° and 137'' respec- 

 tively : both varieties were dianisidine, which thus appears to be 

 dimorphous. No other reduction-product could be obtained. 



All attempts to regenerate the blood-red quinhydronic salts 

 from the "■ quinone " have failed. The basic salts of the above 

 " quinone '" are olive, both solid and in solution, and the acid salts 

 intense purple. With concentrated sulphuric acid the base and 

 the salts give an intense bluish purple even in the minutest traces, 

 as in the case of coerulignone. It is thus probable that the 

 " quinone " does not possess the simple quinone-diimine structure, 

 but instead the isomeric polymerised form : 



CH3O OCH3 



vis., the teframethoxyl-devivative of the asa-xenylaminc (4-4' 

 diamino-arjohisdiphenyl) obtained by the author from "benzidine 

 chromate."" Both the alternative formulas agree with the formation 



of dianisidine by reduction. On the one hand the properties of the 

 substance are stictly analogous to Willstaetter's ''diphenoquinone- 

 diimine," and, on the other hand, the substance is quite stable, 

 does not lose ammonia, and has all the properties of an azo-dye, 

 so that the arguments apply to Willstaetter's compound as well 

 as to the i)resent one : and my opinion is that both have the 

 dimolecular formula, and are aminoazo-dyes. The only difficulty 

 is that the supposed isomeric change of the qiunone-diimine is 

 apparently instantaneous. Even in the most dilute solution the 

 quinhydronic salts give with ammonia a red precipitate of the 

 above base (the dianisidine simultaneously formed remaining in 

 solution), and no sign of an intermediate true quinone-diimine 

 can be detected. 



I'he colour changes of an acid solution of tliis base, 

 CgyHo^O^N^, on evaporation are interesting. The brownisli-green 

 solution in very dilute hydrochloric acid changes to pink, bright 

 reddish purple and dull blue, forming rings on the edge of the 

 vessel which change colour as the steam passes and repasses, with 

 quite remarkable effect. 



The l)ichromate of this base is an insoluble brown precipitate, 

 quite different from the blue quinhydronic bichromate. 



On drying the hydrochloride of the base C.^^Ho^O^N,^ (ob- 

 tained by evaporation) at 105°. it undergoes a further partial 

 change, for on extraction with water, a brown insoluble is left 

 which gives a royal-hluc coloration with sulphuric or strong 

 hydrochloric acid. This is also formed if the hydrochloride is 



* Loc. cit. 



