COMBINED EXPERIMENTAL AND COMPUTATIONAL APPROACHES FOR CHEMICAL-KINETICS INVESTIGATION OF BENZOYL...

The DFT approach at M062x/6311G++(2d,2p) level of theory and UV-vis spectrophotometry methodology were used to explore the kinetics and mechanism of the reaction between substituted benzoyl chlorides (1) and ammonium thiocyanate (2), both theoretically and experimentally. According to the effect of concentration on the reaction rate, the reaction followed secondorder kinetics. The solvent effect shows that mediums with a lower dielectric constant are better for reaction rates. The activation parameters were calculated using the Eyring plot in a lower dielectric constant solvent, such as 1,4 dioxane, where the low value of G (58.7 kJ mol-1) in comparison to polar solvents aids in increasing the reaction rate. In reality, the negative S value (-188.18 J mol-1 K-1) can be offset by the positive H value (lower, 4.01 kJ mol-1). The reaction is entropy regulated in this case, however in the polar solvent (acetonitrile), the unfavourable H value (higher, 45.6 kJ mol-1) can be offset by the favourable S value (-80.9 J mol-1 K-1), resulting in an enthalpy controlled reaction. In both procedures, the effect of various substituents on reaction rate was investigated. On benzoyl chloride, the rate constant favoured strong para electron-withdrawing substituent (EWS) groups (i.e. NO2). In both methodologies, a comparison of theoretical and experimental rate constant values revealed disparities in data. This is to be expected, given the real liquid phase (for experimental purposes) differs significantly from the unlike liquid phase (for theoretical data). According to the Hammet study, the big value of =1.94 indicates that the TS structure is built with negative charges; thus, EWS plays an important role in stabilising the TS character and enhancing the reaction rate. The findings of this research indicated that reactions in the presence of several para-substituted benzoyl chlorides follow the same kinetics. In addition, the theoretical influence of leaving group on the reaction between (1) and (2) was investigated. When compared to benzoyl chloride, the reaction rate in the presence of benzoyl bromide increased by around 25 times in the gas phase and 170 times in the liquid phase. Based on the isokinetic and Exner equations, a linear dependence of H vs S was approved, indicating that the reaction had the same kinetics role in all solvents.

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