Using a stopped flow, the photodiode array spectrometer was employed to study the reduction kinetics of Iron(III)-Benzohydroxamic acid(BHA) complex with pH having 4.5 to 3 and temperature ranging from 298 K to 278 K. KCl was used to set the ionic strength of the system to 0.2 M. Pseudo first-order kinetics were studied to understand the reduction process. The rate constant was also calculated for 2nd order as well. It has been reported that in around 10 to 11 seconds more than half of Iron-BHA complex had been reduced while after around 120 seconds, the concentration of the complex was negligible as was completely reduced. For phase 1, the rate constant with pH 3 for temperature 278 K, 283 K, 288 K, 293 K and 298 K was 0.2120, 0.4310, 0.2900, 0.2770 and 0.5550 M-1 s-1 respectively. For pH 3.5 it is 0.1980, 0.2450, 0.3710, 0.5440 and 0.7150 M-1 s-1. It was 6.5740, 6.5740, 9.8980, 13.1500 and 18.4800 M-1 s-1 for pH 4 and for pH 4.5 it was reported to be 6.5740, 9.8980, 21.0700, 20.3400 and 35.1600 M-1 s-1 respectively. For phase 2, at pH 3 it was reported to be 0.0990, 0.1290, 0.1690, 0.2120 and 0.2750 M-1 s-1 respectively. At pH 3.5 the rate constant was 0.0850, 0.1060, 0.1320, 0.1410 and 0.1790 M-1 s-1. For pH 4, the rate was 6.5740, 6.5740, 17.1300, 25.1600 and 29.5100 M-1 s-1, while it was 6.5740, 6.5740, 10.5500, 42.8000 and 39.3700 M-1 s-1 at pH 4.5 respectively. Thermodynamic parameters were then calculated such as Change in Enthalpy, entropy and activation energy. This study elucidates the thermodynamic and kinetic parameters governing the reduction of the Iron Benzohydroxamic Acid complex. The derived thermodynamic values and proposed kinetic mechanism contribute to a deeper understanding of iron coordination chemistry and redox processes relevant to various chemical and biological systems. These findings provide a foundation for future research exploring similar metal-ligand interactions.
Muhammad Perviaz, Shazia Nisar, Shazia Ishfaq, Kanwal Zahid, Muhammad Atif, Fazal Rahim,
Ajmal Khan and Zulkifle Ikram