164 OXIDATION PRODUCTS OF DIANISIDINE. 



NH.,~v^ V N„ -; V NH. 



and a higher polymer CigH^s^c- i consider, therefore, that no 

 true quinonediimine of the diphenyl-series has yet been prepared, 

 although several quinhydronic substances (so-called " benzidine 

 chromate," and the green oxidation products of dimethyl and 

 tetramethylbenzidine, etc.) are known, and the present paper 

 deals with a new and comparatively stable member of the 

 quinhydrone class. 



A. Salts af Dianisimino-quinhydrone. — The chloride is very 

 easily obtained by dissolving dianisidine in excess of dilute 

 hydrochloric acid at not over 25°, and suddenly adding a slight 

 excess (over the theory) of strong ferric chloride solution. The 

 mixture becomes immediately deep blood-red, and the quin- 

 hydronic chloride almost immediately crystallises out in deep- 

 indigo microscopic needles, quite black in the liquid, and com- 

 pletely opaque under the microscope. Great excess of ferric 

 chloride, or too high a temperature, lead to an impure product: 

 otherwise the reaction is nearly quantitative. The presence of 

 strong acid prevents the separation of the indigo compound 

 (which is the wo/zo-hydrochloride*, and is soluble in strong acids 

 to a deep blood-red colour, still visible in a dilution of i part in 

 a million, presumably due to a diacid salt). 



The preparation is washed on a Buchner funnel until iron is 

 removed and the substance begins to dissolve with a greenish- 

 blue colour: further washing leads to partial hydrolysis: an 

 olive-green coloration of the washings is seen when the free acid 

 is almost gone, this being a mixture of the blood-red and i>lue- 

 green colorations of the diacid and monacid salts respectively. 

 For analysis, the substance was dried over sulphuric acid in vacuo. 

 0.2390 gram reduced by standard stannous chloride in presence 

 of hydrochloric acid, and back-titrated by iodine used 0.0477 >'^''' 

 in the reduction — 19.95^^'. 



0.1810 treated with silver nitrate excess and boiled to de- 

 struction with concentrated nitric acid gave silver chloride, which 

 was weighed as Ag after reduction : Ag := 0.0S05 : hence HG in 

 substance = 15.0%. Iron impurity in filtrate found 1% 

 = 1.9% HCl as FeCla, therefore corrected HCl in substance 

 := 13. 1 %. "By removing tin from the reduction-liquor by sul- 

 phuretted hydrogen and adding ammonia the reduction product 

 was obtained, and was pure dianisidine (;»./'. 137°). 



Dianisiminoquuihy drove mojwhydrochloridc. — 



NH 



CH3O OCH3 



r= CosHooOjN^Clo on the official formulation 

 requires HCl =: 13.1%, Sn for reduction to dianisidine == 21.3%. 



'*' This is on the C, . formula. 



