Defining pH-dependent equilibrium reactions as a solution to overcome the correlation between kinetic parameters

It is a well-known fact that in first-order reverse reactions (A■(k_1@⇄@k_2 )B), the rate constants cannot uniquely be determined from incomplete concentration data. This is due to the correlation between the rate constants. Several well-conducted studies have investigated the theoretical basis and visualization of the correlation for reversible first order reaction schemes [1]. Therefore, breaking this correlation is necessary to determine the rate constants. In this work, coupled equilibrium kinetic processes suggested as a new strategy to overcome this problem. Also, this fact opens the possibility to determine kinetic parameters in multi-step kinetic reactions (scheme.1). The complete analysis of the complex reaction mechanisms with the possibility of calculating and inserting the equilibrium and kinetic parameters into the fitting algorithm are possible by model-based global analysis. After the fitting process, the optimal equilibrium and kinetic parameters together with an estimate of their standard deviations have been obtained [2-4]. Therefore, in the following, datasets have been simulated for a range of different chemical cases and the pH-dependent keto–enol tautomerization chosen as the experimental case of equilibrium intertwined with kinetic chemical mechanisms (E+H□(↔┴Ka ) EH⇄KH). Herein, the keto–enol tautomerism kinetics of 1-phenyl-1,3-butadione (benzoylacetone, BZA) in aqueous solution has been simulated and investigated in buffered medium in the UV–Vis spectra of BZA at the range of 200-400 nm in 5°C. This system has been monitored for 5 min. Our proposed equilibrium-kinetic model provides rank deficient single data sets which can be broken by matrix augmentation through pH and temperature changes. Different pHs used as an appropriate and convenient augmentation strategy in this study to allow the extracting the equilibrium and kinetic constants.