Synthesis and Characterization of Novel Nitroaniline-Based Azo Compounds as Acid-Base Indicators

Abstract

Nine new azo compounds (Y1-Y9) were synthesized in this work by diazotizing ortho-, meta-, and para-nitroaniline derivatives and then coupling them with either 2,7-dihydroxynaphthalene, 8-hydroxyquinoline, or α-naphthol. The reactions were carried out in an ice-bath at 0-5 °C under strictly regulated basic conditions. Using DMSO-d₆ as the solvent, Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy (¹H and ¹³C) were used to characterize the structures of all produced compounds definitively. UV-Vis spectral shifts in DMSO solutions across a wide pH range (1-14) were examined to measure their effectiveness as acid-base indicators. Both protonation and deprotonation caused noticeable bathochromic shifts in the compounds. The cationic form (pH 1-7) exhibited absorption maxima (λmax) at 391-483 nm, whereas the anionic form (pH 8-14) absorbed at 448-587 nm. These sharp and reversible color changes, which correspond to pH ranges of 7-10, demonstrate the effectiveness of the synthesized azo compounds as effective acid-base indicators in analytical chemistry, offering potential alternatives to conventional standards.