Ten novel azo acid dyes were synthesized from benzimidazole derivatives using H-acid, Gamma acid, J-acid and Tobias acid as the coupling components and both the synthesized intermediates and the dyes were characterised and their properties and structures confirmed using UV–Visible, FT-IR and 1H NMR spectroscopic techniques. The dyeing efficiency of the dyes was investigated on nylon 6, 6 fabrics, and the fastness to perspiration, light and washing were assessed. They showed very good percentage exhaustion (64–89)% on nylon 6, 6 with bright and dark intense hues of red, blue and purple. The novel azo acid dyes showed very good to excellent (4–5) fastness to perspiration, fair to very good fastness to light (3–6) and also fair to very good fastness to washing (2–4). The dyes showed moderate fastness results when compared with a commercial acid dye, Serilene Dark Red FL (4–5; 7 and 5 for fastness to perspiration, light and washing).
The novel dyes outperformed similar acid dyes produced in 2023 by two different researchers in terms of wash fastness and light fastness on nylon 6, 6 fabrics.