COMPOUNDS CAUSING RED COLORATION OF ANILINE: I. 



13 



2,5-dianilinoquinonediaml (azophenine) was identifid by its very 

 characteristic crystalline form, and the coloration produced with con- 

 centrated sulphuric acid. The crystals employed for the purpose of 

 comparison were made by oxidizing aniline with iodic acid 14 in the pres- 

 ence of the required concentration of acetic acid. The compound was 

 recrystallized from aniline. 



0. Lehmann" describes the crystals as monoclinic needles from aniline which 

 unite extraordinarily often to twins which cross, with pronounced tendency to 

 bending, and which are very dichroi'c. Beilstein lG gives the description, garnet- 

 red leaflets. 



I am indebted to Dr. W. D. Smith for the following description of 

 the crystals. The accompanying figures show the characteristic forms. 



Fig. 4. 



Orthodomes 

 (.00 



-Orthopirwcod 

 (100) 



V 



Fig. 



The compound crystallizes in the monoclinic system and by reflected light 

 appears garnet-red in color. The crystals, which appear almost invariably as 

 shown in fig. 4, measure much under a millimeter in length, one of the longest 

 in a group measuring 0.18 millimeter. They are very pleochroic, varying from 

 colorless through yellow to garnet-red. The crystals usually occur in halves, 

 the normal crystallization being as shown in fig. 7. In fig. 6, a twin is shown, 

 the twinning angle being 31°, the same as the extinction angle. The index of 

 refraction is medium. The double refraction is strong, the interference colors 

 are reds and blues of the second order. 



All of the compounds which have been isolated are soluble in aniline 

 with the production of colored solutions. The following is a brief 

 study of the solubilities : 



Azophenine is somewhat soluble in alcohol and aniline and is readily crys- 

 tallized from either solvent. The solutions are brilliant red. 



2, 5-dianilinoquinoneanil is soluble in alcohol and aniline, the solutions being 

 brilliant red. 



2, 5-dianilinoquinone is practically insoluble in alcohol and soluble in aniline, 

 forming a brilliant red solution. 



Azobenzene is very soluble in aniline forming a reddish-yellow solution. 



The power of the first three compounds of coloring colorless aniline is intense 

 and exceeds by many fold the coloring power of the latter compound. 



14 Ostrogovich and Silbermann: Chem. Abs. (1908), 2, 1433. 

 "Jahresb. d. Chem. (1882), 369. 

 "Handbuch, Org. Chem. (1897), 3, 341. 



