Abstract

The kinetics of azo-chalcone dye formation from (E)-1-(4-nitrophenyl)-3-phenylprop-2-en-1-one and diazotized 4-aminobenzoic acid were investigated. Chalcones exhibit valuable biological and optical properties, yet the kinetic parameters governing their azo-coupled derivatives remain incompletely characterized. This study aimed to determine the reaction rate constants, activation energy, and half-life for azo-chalcone dye formation under varying temperatures, and to validate the experimental findings using density functional theory ( DFT ) calculations. UV-Vis spectroscopy monitored the dye formation at 346 nm over 130 min at four temperatures ( 275, 285, 295, and 305K ) under natural pH and optimized 1:10 stoichiometric ratio ( Chalcone reagent ). Pseudo-first-order kinetic analysis and the Arrhenius equation were applied. DFT calculations using the B3LYP/6-31G method were performed with Gaussian 09. The reaction followed pseudo-first-order kinetics (R² = 0.9627 – 0.9887). The rate constant increased from 0.0529 min⁻¹ at 275K to 0.0616 min⁻¹ at 305K, with corresponding half-life decreases from 13.1 to 11.3 min. Arrhenius analysis yielded an exceptional linear correlation (R² = 0.9999) and an activation energy of 3.54 kJ mol⁻¹. DFT calculations identified nitrogen and oxygen atoms as the primary donor-active sites. The temperature-dependent kinetic behavior aligns with literature on azo-imine dye formation, indicating a low energy barrier and minimal thermal sensitivity for the pseudo-first-order proces. DFT validation supports the spectroscopic observations and elucidates the electronic properties governing reactivity. The azo-chalcone dye formation follows pseudo-first-order kinetics under the optimized conditions. The rate constants increase with temperature, and DFT confirms the reaction mechanism. These findings contribute to understanding azo dye synthesis for potential biological and optical applications.