THE COMPOUNDS WHICH CAUSE THE RED COLORATION 

 OF ANILINE: I. THE EFFECT OF OXYGEN AND OZONE 

 AND THE INFLUENCE OF LIGHT IN THE PRES- 

 ENCE OF OXYGEN. 



By H. D. Gibbs. 



(From the Laboratory for the Investigation of Foods and Drugs, Bureau of 



Science, Manila, P. I.) 



The cause of the formation of the red color in aniline has been attrib- 

 uted to impurities and to oxidation. The literature does not contain 

 as great a mass of confused and inacurate statements upon this subject 

 as upon the question of the coloration of phenol. 1 



A. Rosenstiehl 2 remarks that, as is well known, aniline is turned brown in 

 the air. On neutralizing with acid the color turns to rose due to the formation 

 of pseudorosaniline by oxidation. 



He exposed aniline in a balloon flask to the action of air in the sunlight for 

 three months and distilled the contents of the flask in vacuo. The distillate was 

 pure aniline and the residue in the flask on acidification was colored rose, due to 

 rosaniline. 



A. Bidet 3 states that pure aniline and its homologues are colorless when 

 freshly distilled, become yellow after some days, but never acquire the dark tint 

 of the impure compounds. He ascribes the color to thiophene and thiophene 

 derivates and believes that the coloration of benzene compounds is a much more 

 delicate test for thiophene than the isatin reaction. 



P. Werner * also recalls the well-known fact that when aniline is exposed to 

 air and light it becomes colored, first yellow, then red and finally brown. He 

 placed samples of pure, colorless aniline in vacuo, in oxygen and in air in the 

 diffused daylight for three and one-half months and corresponding samples in 

 the dark. Those in vacuo remained colorless. The samples in oxygen and air 

 in the daylight were colored and absorbed considerable quantities of oxygen, 

 while in the dark the coloration was slight and the oxygen absorption in the 

 tube containing oxygen was "very slight," and in the tube containing air 

 "inappreciable." 



From these data he concludes that the coloration is proved to be due to 

 oxidation caused by the combined action of light and oxygen (air). 



'Gibbs: This Journal, Sec. A (1908), 3, 361. 

 -Compt. rend. Acad. sci. (1876), 82, 380. 

 *Compt. rend. Acad. sci. (1889), 108, 520. 

 '.Tourn. Soc. Chem. Ind. (1890), 9, 278. 



