Organic dyes- Indigo and Azo dyes Results and Discussion PDF

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lab report for organic dyes of indigo and azo dyes...

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Hudgins 1 Shannon Hudgins Sryashi Sinha CHEM 238 28 July 2021

Organic dyes- Indigo and Azo dyes: Results and Discussion

Introduction In this experiment indigo and azo dyes were used to analyze the effects of dyeing fibers. Dyes have a wide range of history in our world. Indigo originally came from plants, such as ones from India and Europe. Dyes are chemicals that can change the reflecting wavelength, so a different color will be projected. This happens through the alteration of pi and sigma bonds in a compound. Since indigo is soluble, it has to be reduced to be used as a dye. Indigo is synthesized by using 2-nitrobenzaldehyde, acetone, and NaOH to produce leucoindigo. The general mechanism for this reaction is shown in Figure 1. The fabric is dyed with the leucoindigo, but when dried the leucoindigo oxidizes back to indigo due to the oxygen in the air. On the other hand, azo dyes are easily synthesized and do not fade in the air. These molecules contain an azo group and are the 60-70% of dyes found in the food, textile, and leather industry. The color changes in azo dyes by changing the structures of the groups that bond to the azo dyes. The reaction of azo dye happens in two steps. The aromatic primary amine is first changed into a diazonium salt. After that, a reactive aromatic ring is added, which is normally a phenol. The reaction for azo dyes is an electrophilic aromatic substitution, which is shown in Figure 2.

Hudgins 2 Figure 1: Mechanism of Indigo

Figure 2: Mechanism of Azo

Summary of Results After analyzing each strip of fabric, it clearly shows the colors that were created. With the indigo strip, the fabrics with the deepest color were Filament Acetate, Nylon 66, and Worsted Wool. The weakest color fabric of indigo was Polyacrylic. The assigned dyes for azo were A1, B1, and C2 to compare. The given dye was C2. The C2 had the deepest color on Nylon 66, Worsted Wool, and silk and the weakest on Polyacrylic. The fabrics with the deepest color on B1 were Nylon 66, Worsted Wool, and silk. The weakest colored fabric for B1 was Polyacrylic. The fabric with the deepest color on A1 was Worsted Wool and the weakest was Polyacrylic. The

Hudgins 3 fabric stained the deepest was C2. The fabric stained the weakest was B1. After calculating the percent yield to be 136%, it shows there are impurities in this dye.

Possible sources of error and probable solution Some errors that could have occurred in this experiment, could have not been washing the fabric. If the fabric was not washed, it would be harder to compare the results of the experiment. One way to fix this, is to follow the directions as given and wash and dry the fabric properly. Another error could have been no vacuum filtrating the dye properly and causing impurities in the dye. This could lead to false results. A way to fix this is to purify the sample as best as possible.

Discussion of Results In conclusion, this experiment was a success. The dyes were successfully used to observe the fabrics. The azo dye tends to bind to the Worsted wool the best. Wool holds a great amount of polar groups because these bonds are meant for hydrogen bonding, so it makes it easier for the dye to hold onto the fabric. The fabrics containing less polar bonds hold dye poorly. Some examples of these fabrics were Polyacrylic and acetate. In comparison of the three azo dyed fabrics given, the C2 fabric had the deepest strongest color, while the B1 had the weakest color. When it comes to the activating or deactivating groups in these fabrics, the activating groups increase the rate of a reaction, where the deactivating groups decrease the rate of the reaction. This means the azo dyes with activating groups created a more intense deep color....