In the process of the experiment, the dark red color was produced through the coupling 4-aminobenzenesulfonic acid and 1-naphthol while the reaction of 3-aminobenzenesulfonic acid and 2-naphthol resulted in the dark orange color generation. In the first case, adding hydrochloric acid to the produced azo dye led to the change of the color from dark red to orange, and the reaction with sodium hydroxide resulted in the change from dark red to red wine color; in the second case, the reaction with hydrochloric acid caused the change from dark orange to light orange, and adding sodium hydroxide led to dark orange to orange.
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Since two different dyes that were used in this experiment are characterized by different structures and wavelength of light absorption, they are different colors. Within a dye, there is a color-bearing group, chromophore, that becomes the reason for a certain color. Besides, there may be so-called auxochromes, or “color helpers,” that intensify the effect or change it a little, such as carboxylic acid, sulfonic acid, amino, and hydroxyl groups.
In case of 4-aminobenzenesulfonic acid + 1-naphthol, it is the presence of 1-naphthol that produces red. The delocalization of electrons is more; consequently, the waves are longer. In the second case, the chromophore is 2-naphthol that is placed in a different way within the molecule. Consequently, this phenomenon produces orange. The structure also influences the reaction with HCl and NaOH. In the first case, if HCl is added, the level of the pH becomes higher, and the color is lighter.
NaOH makes the level of the pH lower, and the color becomes darker. In the second case, however, dark orange changes in both cases because this dye is less pH sensitive owing to the presence of 2-naphthol.
As the experiment demonstrated, the colors of the dyed multi-fiber strips were diverse. Natural fabrics, especially wool, were affected most: the colors turned out to be the richest. The same is relevant to cotton: the colors are only slightly brighter. It can be explained by the structure of fabrics. Wool has numerous charged groups in its structure while other fabrics do not demonstrate such attributes in their usual repeating units. In addition, nylon, as well as wool, has amide-linking groups in its repeating units; one may state that the polar amide groups react upon each other to a great extent through the hydrogen bonding. In comparison with wool, cotton, and nylon, acrylic fabrics, polyester, and acetate were colored less intensively since they are not hydrophilic and absorbent.
|Dye||The degree of absorption|
|4-aminobenzenesulfonic acid + 1-naphthol (dark red)||High (the most consistent color)||Low||Low||Middle||Middle||Low|
|3-aminobenzenesulfonic acid + 2-naphthol||High (the most consistent color)||Low||Low||Middle||Middle||Low|
Carrying out the experiment, I did not encounter serious problems and followed the given instructions carefully. However, I had to use a little different proportions of the reagents in order to ascertain that there would be enough dyes. The fabric strips seemed to be large, and I doubted that I would be able to work with all types of fabrics. I calculated how much matter I needed, but I received fractional numbers and rounded them off. This fact probably influenced the accuracy of the experiment. Except for this change, the experiment was conducted according to the instructions.