Demonstration of aniline black dye

Chemicals needed

aniline T N R 20/21/22-40-48/23/24/25-50 S (1/2)-28-36/37-45-61

distilled water

sulphuric acid potassium dichromate solution T+ C N R 21-25-26-35-37/38-41-43-46-49-50/53 S (1/2)-26-45-53-60-61

Equipment needed

test tube

Test procedure

Safety goggles! Avoid touching the reagents or the reaction mixture, aniline can cause cancer!
One adds about 0.5 ml water and then adds 3 drops aniline.
Now one adds about 0.3 ml of the dichromate solution and sways the tube carefully back and forth. Within a few seconds a blue-black color arises which then rapidly becomes darker.

Disposal

The residues can be disposed of as halogen-free organic waste. The dye residues can be largely removed with acetone or the like and a brush (caution!).

Elucidation

Through oxidative coupling aniline combines with itself, thereby forming chains of different lengths. Inasmuch as it is a matter of conjugated Pi-electron systems with various absorption maxima, the coloration covers the entire color spectrum. The structure of aniline black dye can be approximately described as:

Photos

Aniline black dye

Literature

to be added