10 GIBBS. 



From his experiments lie seems hardly to be justified in stating that 

 the combined action of light and air are necessary, for, while the aniline 

 in vacuo remained colorless both in the dark and in the light, in the 

 presence of air or oxygen a coloration was noticeable in the dark as well 

 as in the light; so that the action of light, in the presence of oxygen, 

 would simply seem to accelerate the reaction. 



Hantzsch and Freese 5 believe that the color is caused by a thiophene derivative. 

 They state that aniline to which 0.5 per cent of thiophene has been added 

 distills with an intensely yellow color, while a sulphur-free aniline distills without 

 color and remains colorless for weeks. 



Since the literature offers only two explanations, impurities and 

 oxidation, for the cause of the coloration, the various text-books have 

 chosen either one or the other. The following are a few of the statements 

 found. 



Meyer and Jacobson ° state that the usual preparations of aniline are quickly 

 turned yellow to brown by light and air. The color appears in the presence of, 

 and depends upon, small amounts of a sulphur compound. 



Roseoe and Schorlemmer 7 state that aniline "on exposure to light and air 

 becomes brown and the more impure it is the more rapidly does this coloration 

 take place." 



Allen s states : "Aniline becomes yellow or brown on exposure to air and light, 

 especially at elevated temperatures, a resinous body being ultimately formed. 

 The change is due to oxidation and does not occur in vacuo or in the dark." 



Holleman- Walker " state: "Aniline is a colorless liquid, and, unless perfectly 

 purej turns brown in the air, the color change being probably due to the presence 

 of traces of sulphur compounds." 



I have found that the cause of the coloration of pure aniline in the 

 presence of oxygen is oxidation. Azobenzene, dianilinoquinone, dianil- 

 inoquinoneanil, and azophenine have been isolated from the red aniline, 

 but are hy no means the only substances produced by the oxidation. Since 

 the oxidation, because of the presence of the quinone derivatives, has been 

 shown to go as far as quinone, it is reasonable to expect that intermediate 

 products are formed at least as transition compounds, and that these exist 

 in the aniline solution if they escape further oxidation and do not readily 

 form condensation products. 



The fact that the three quinone condensation products, dianilinoqui- 

 none, dianilinoquinoneanil, and azophenine, have been isolated would 

 seem to indicate that they all exist in the aniline solution. This, how- 

 ever, is by no means proved for the reason that the methods employed for 

 their isolation may convert, at least in part, one derivative into another. 



°Ber. d. deutschen ohem. Ges. (1894), 27, 2529 and 2966. 



"Organische Chemie, Leipzig (1902), 2, 168. 



'Treatise on Chemistry, New York (1897), 3, pt. 3,199. 



8 Commercial Organic Analysis, Philadelphia (1892), 3, pt. 2, 43. 



; ' Text-book of Organic Chemistry, New York (1906), 370. 



