Structure dependence of the rate coefficients of hydroxyl radical+aromatic molecule reaction

Abstract

The rate coefficients of hydroxyl radical addition to the rings of simple aromatic molecules (kOH) were evaluated based on the literature data. By analyzing the methods of kOH determination and the data obtained the most probable values were selected for the kOH's of individual compounds and thereby the most reliable dataset was created for monosubstituted aromatics and p-substituted phenols. For these compounds the rate coefficients fall in a narrow range between 2×109mol−1dm3s−1 and 1×1010mol−1dm3s−1. Although the values show some regular trend with the electron donating/withdrawing nature of the substituent, the log kOH−σp Hammett substituent constant plots do not give straight lines because these high kOH's are controlled by both, the chemical reactivity and the diffusion. However, the logarithms of the rate coefficients of the chemical reactivity controlled reactions (kchem), are calculated by the equation 1/kOH=1/kchem+1/kdiff, and accepting for the diffusion controlled rate coefficient kdiff=1.1×1010mol−1dm3s−1, show good linear correlation with σp.