COMPOUNDS CAUSING BED COLORATION OF ANILINE: I. 11 



EXPERIMENTAL. 

 ANALYSIS OF THE ANILINE COLORED BY THE PRESENCE OF OXYGEN AND SUNLIGHT. 



Samples of 100 cubic centimeters of aniline in 200 cubic centimeter bottles 

 were placed in the direct sunlight and constantly agitated for about one month. 

 The stoppers were removed from time to time and the air over the liquid changed. 

 The aniline quickly became light yellow and finally, after passing through the 

 intermediate stages, an intense deep red. 



Separation of the reaction products was affected in several different ways. 

 On pouring 20 cubic centimeters into a large volume of very dilute sulphuric 

 acid, the aniline all dissolves as aniline sulphate. A residue which does not 

 dissolve imparts to the mixture a reddish-brown color. After filtration the almost 

 colorless solution changes to yellow and finally assumes a red color on standing. 

 From the insoluble portion on the filter there was isolated 2, 5-dianilinoquinone. 



Other separations were made by extracting the dilute sulphuric acid solution 

 of the colored aniline, without removing the suspended precipitate, repeatedly 

 with small quantities of ether. The larger proportion of the precipitate went 

 into the ether, forming a red solution. The etherial solution was filtered and 

 evaporated in a vacuum dessieator. The residue separates in layers, one red 

 and another a dark purple, almost black. The red portion was soluble in alcohol 

 and was separated by this solvent. Dianilinoquinone was identified in the 

 insoluble portion. The red alcohol solution lost its color on treatment with 

 nascent hydrogen and other reducing agents. On slow evaporation yellow-brown 

 needles of dianilinoquinoneanil separated. Another portion of the alcohol solution 

 was warmed until the alcohol had evaporated. The red residue was distilled 

 with steam. A few drops of an orange- red oil. which solidified to orange-red 

 crystals, passed over with the steam. These crystals were readily reduced in 

 alcoholic solution to hydrazobenzene. Azobenzene must, therefore, be present. 



Other separations were made by slowly pouring 20 cubic centimeters of the 

 aniline into 100 cubic centimeters of 50 per cent acetic acid. On cooling the solu- 

 tion in ice, a large number of srnall crystals separated. When viewed with the 

 microscope they were recognized on sight as azophenine. The marked tendency to 

 twinning is quite characteristic. A very few crystals of dianilinoquinone were 

 also observed. 



Twenty cubic centimeters of the colored aniline were distilled in steam until 

 the volatile compounds had passed over. The red residue in the flask was 

 filtered and the precipitate dissolved in a small quantity of hot alcohol. On 

 standing, crystals of azophenine separated. 



2, 5-dianilinoquinone was identified by its ciwstalline form, high melt- 

 ing point and coloration produced with concentrated sulphuric acid. 

 Since the descriptions of this compound given in the literature are in some 

 points conflicting, a study of some of its properties has been made. 



The appearance of the crystals is described by A. W. Hofmann, 10 who first 

 prepared the compound, as "reddish-brown almost metal lustrous scales;" by 

 Knapp and Schultz "■ as "brown-red, metallic glistening, leaflets;" by Zincke 

 and Hebebrand 12 as "small, bluish-violet leaflets," and by Nietzki and Schmidt 13 

 as "steel-blue, glistening leaflets." 



10 Proc. Roy. Soc. (1863), 13, 4. 



11 Ann. d. Chem. (Liebig), (1881), 210, 179. 



12 Ber. d. deutschen chem. Ges. (1883), 16, 155G. 

 "Ibid. (1889), 22, 1655. 



