New Heterocyclic Azo Dyes: Design, Synthesis, and Application on Leather

Heterocyclic azo dyes are an important class of azo dyes well known due to their widespread applications as colorants and functional materials as well. In the present investigation, synthesis of a new series of heterocyclic azo dyes (6a-i) based on pyrazole core is portrayed. The synthetic strategy involves the diazotization of 4-aminoacetanilide (1) followed by coupling with different active methylene compounds in alkaline medium to afford intermediates (4a-d). The latter, on condensation, with separately synthesized substituted hydrazines (5a-d) afforded the target dyes (6a-i). The structures of newly synthesized dyes were established by ¹H and ¹³C nuclear magnetic resonance spectroscopy, infrared spectroscopy, and elemental analysis. UV-Visible absorption study of synthesized dyes was conducted and λ_max was found in the range of 388–401 nm. Furthermore, these dyes were applied on leather as a topcoat and found to exhibit moderate to high values of the application parameters such as light fastness, wash fastness, and rubbing fastness.