The first step in the oxidation of the para-phenylene-diamine is the formation of quinone di-imine, NH:C6H4:NH. This is a very unstable compound in the free state, and even in aqueous solution it decomposes within a comparatively short time, or combines with itself to form a more stable substance. Quinone di-imine has a very sharp, penetrating odor, and produces violent local irritations wherever it comes in contact with the mucous membrane. If a small quantity of para-phenylene-diamine is absorbed into the human body, by breathing the dust, or otherwise, the formation of quinone di-imine takes place internally with consequent irritation of the mucous lining throughout the body. The various pathological conditions mentioned before may be ascribed to irritation caused by quinone di-imine. In any dyeing process where there is a possibility of the formation of quinone di-imine, as is the case with most dyes containing para-phenylene-diamine, special precautions must be taken by the workers in handling the dye or coming in contact with its solutions, and no one who is particularly sensitive to irritation should be permitted to work in a place where such dyes are used.
The next step in the oxidation of the para-phenylene-diamine is the formation of what is called Bandrowski’s base. Three parts of the quinone di-imine combine with themselves, forming a substance of a brown-black color, which was formerly regarded as the final oxidation product. The formula of Bandrowski’s base is represented by the following chemical hieroglyphics:
| (NH2)2.C6H3.N:C6H4:N.C6H3(NH2)2 . |
Further investigation has shown that the oxidation proceeds beyond this stage with the formation of a compound of what is known as the azine type, which is depicted by the chemist as
| NH | NH | |||||||
| (NH2).C6H3 | < | > | C6H2 | < | > | C6H3.NH2. | ||
| NH | NH |
It is by no means certain that this substance is the true coloring matter obtained by the oxidation of para-phenylene-diamine, for the reactions may continue still farther, producing even more complicated oxidation products. Scientific research and study has not as yet gone beyond this stage.
The reactions of the other dyes of the Oxidation type are quite similar to those of para-phenylene-diamine, some being simpler, and others being even more complex. The presence of certain chemical groups in the intermediate, or the relative position of such groups are factors responsible for the variations in shade.
With the various mordants, the Oxidation Colors give different shades, and a great range of colors can be produced either by combining mordants, or combining dyes, or both. The following tables illustrate the shades formed with the customary mordants.
| Chrome | Copper | Iron | Direct | |
|---|---|---|---|---|
| Ursol D | brown black | coal black | coal black | dark brown to brown black |
| Ursol P | dull red brown | dull dark brown | grey brown | light brown |
| Ursol 2G | yellow brown | dull yellow brown | yellow brown | dull yellow |
| Ursol A | ... | ... | blue black | blue to blue-black |
| Ursol 4G | light brown | medium brown | yellow | pure yellow |
| Ursol 4R | orange brown | light yellow brown | red brown | orange red |
| Ursol Grey B | greenish grey | greenish grey | mouse grey | ... |
| Ursol Grey R | brownish grey | brownish grey | reddish grey | ... |
Fur dyes of American make being equal in every way to the German product, show the same color reactions with the various mordants. The following table shows the shades produced with the same mordants as above: