Correlation of reactivity indices with thermodynamic and kinetic parameters of the benzoyl peroxide decomposition

The indices of reactivity (electronic chemical potential, chemical hardness, electrophilicity index, charge change in the system "benzoyl peroxide — monomer (solvent)") of such monomers as N-vinylpyrrolidone, methyl methacrylate, maleic anhydride, acrylonitrile, styrene, and solvents — N-methylpyrrolidone, acetonitrile, toluene. The indices have been compared with the calculated (B3LYP/6-31+G(d)) activation and thermodynamic parameters of the scrambling reaction of benzoyl peroxide and its interaction with some monomers (solvents). It has been found that the introduction of molecules of the considered monomers or solvents in the scrambling reaction increases the barrier ∆G^≠ (decreased the rate) of benzoate radical recombination in the cell, which should increase the proportion of free radicals in the initiation stage. It has been found that the scrambling activation enthalpy value decreases linearly with an increase in the chemical hardness of the compound medium, whereas the activation enthalpy and the reaction of the addition of a benzoate radical to a monomer (solvent) molecule correlate with all indices, except for chemical hardness. There is no correspondence between the rate constant of peroxide decomposition in the medium of monomers (solvents) (ln kd) and the calculated parameters ∆G^≠ (or ∆G), as well as the chemical hardness of these compounds, while the other indices have shown a correlation with ln k_d. The difference in correlation dependences for compounds containing the lactam cycle (N-vinylpyrrolidone, N-methylpyrrolidone) and other monomers and solvents is shown. An assumption about different mechanisms of the decomposition of benzoyl peroxide in the considered media has been made.

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