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Introduction
Azo dyes are the most popular dye materials that cover more than 50% dye market. The azo group is the main feature of all organic dyes; it joins the aromatic rings that result in an extended conjugated multiple bonds system. The unique characteristic of organic dyes is that they possess the colour. The reasons behind this uniqueness are the light absorbance in the visible spectrum (400–700 nm) and presence of at least one chromophore (colour-bearing group). Their conjugated system and resonance of electrons also produce color effect (Banks, Smart & Tatlow, 1994). Azo composites are created by the reaction of a primary aromatic amine with nitrous acid, HNO2. The result is a diazonium ion.
Scheme of synthesis of Fast red A dye
This ion can pair with a nucleophilic aromatic compound, like phenol or an aryl amine and produce the azo compound. In this azo coupling process, a cation from terminal nitrogen performs an electrophilic attack on activated aromatic compound. It happens at para position to produce dye material.
Dye molecules attach to the fiber molecules in cloth by various means as via van der Waals forces, electrostatic attraction, hydrogen bonding or covalent bonds (Wang, Shen & Xu, 2000). The higher the number of polar groups in the fiber molecule, the more chances of easier die for fabric. The method of making dyes through diazonium salt came into limelight in middle of 19th century. Apart from fabric azo dyes are used in paint, food, cosmetics. However, some countries have banned their use in food due to its toxicity and their adverse effect on children.
Though the dye-substrate appeal is significant, but synthetic dyes are linked little health risk under several conditions. Therefore, environmental safety is a vital consideration kept in mind during molecular designing. Thus, the basic materials engaged in the manufacturing of c dyes should not contain such compounds known to cause a health hazard. A large group of aromatic amines are found cancer-suspect agents and have acted as mutagens in the standard Salmonella mutagenicity assay (Reife & Freeman, 1996). For azo dyes, it is assumed that the intact aromatic amines dye could be safe but its metabolites can generate mutagens. For instance, Direct Red 28 could lead to the formation of the benzidine if it is taken up inside the body that is a bladder carcinogen.
Aim
This experiment aims to synthesize an azo dye, Fast red A (Acid red 88) and analyze its appearance and yield. Also target to dye some material like wool, cotton and nylon and observe the appeared color and its stability and similarity on different fabrics.
Materials and Method
8 drops of 85% phosphoric acid were added to 5 ml distilled water in a conical flask. Now 0.65 gm naphthionic acid was added to it and stirred in a magnetic stirrer. Afterwards, the solution was fixed in the ice bath and stirred for more 10-15 minutes. Meanwhile, another solution of 2-naphthol was prepared by dissolving 0.40 gm 2-naphthol in 2.5 ml, 2M NaOH in a beaker of 50 ml. After complete dissolution, it was placed in an ice bath.
After 15 minutes on the ice bath, 0.20 gm sodium nitrite was added to the amine solution. The color change was obvious. To spin the contents flask was removed from the ice for a while and again re-clamped and left on ice for more 5 minutes. Now the solution of 2-naphthol was added to this solution and stirred with a metal spatula in the ice bath for further 5 minutes. After 5 minutes, it was removed from the ice and let it adjusted at room temperature, sometimes stirring. Liquid was boiled on a Bunsen burner, before collecting via vacuum filtration. The appearance and yield of the product were noted down. Dye was kept in a vial.
After the successful yield of the dye, it went through fastening test. 100 ml distilled water was taken in a beaker and a small amount of dye was added to it with 5 drops of acetic acid. Solution was heated until started boiling and then a piece of cotton wool was dipped for a minute. This cotton wool was removed and washed under hot running water before drying it. This procedure was repeated with woolen string and nylon material.
Results and discussion
The produced dye product was reddish brown in color, and total amount of the product was 1.02 gm (21.6 gm with vial, where 20.58 gm weight for vial). When amine solution was mixed with sodium nitrite, it showed the color changed to yellow. In fastening test on dipping, cotton wool yielded dark reddish color, woolen string showed dark pink color while nylon material showed light pink color. During the method, ice bath was used to maintain the instability of diazonium ion so that it can pair with a nucleophilic aromatic compound to deliver a stable dye compound.
The produced Fast Red A acid dye obtain its acidity from the presence of sulphonic acid group (–SO3) in the molecule. It is water-soluble anionic dye, applied to nitrogenous fibers like wool and nylon that contain basic groups. The fastening test result of dye indicates the stable color even after washing because of the fibers attachment on its cationic sites (Musa et al., n.d.).
This result advice that dye has high exhaustion for both nylon and wool fabrics but nylon showed higher exhaustion due to its open structure. All three fabrics showed good color fastness properties to nearly similar, with a little variance in color.
References
Banks, R. E., Smart, B. E., & Tatlow, J. C. (Eds.). (1994). Organofluorine chemistry:
principles and commercial applications. Springer.
Musa, H., Abdulmumini, A., Folashade, M. O., Usman, B., & Abba, H. (n.d.) Studies on the
Dyeing Of Wool and Nylon Fabrics with Some Acid Dyes.
Reife, A., & Freeman, H. S. (Eds.). (1996). Environmental chemistry of dyes and pigments. John
Wiley & Sons.
Wang, S., Shen, S., & Xu, H. (2000). Synthesis, spectroscopic and thermal properties of a series
of azo metal chelate dyes. Dyes and pigments, 44(3), 195-198.
