We investigated the relationship between molecular structure and reactivity for the peroxidase mediated coupling of substituted anilines and phenols. We undertook this study to gain a better understanding of the oxidative coupling processes operative in soil involving peroxidase enzymes. The relative reaction rates of the various substituted aniline and phenol compounds (electron donors) were determined by measuring electron donor disappearance using high pressure liquid chromatography. The effects of structure on reactivity were treated quantitatively by use of the Hammett equation. We found a good correlation between electron donor rate constants and their respective Hammett substituent σ + constants which indicated the formation of a positively charged transition state as the rate controlling step. The ρ values obtained from these correlations were negative, demonstrating that reactivity was increased by the presence of electron‐donating substituents on the aromatic ring which act to stabilize the positively charged transition state. These results suggested that the reaction rates depended on electron density at the reaction center (−NH 2 or ‐OH) in a predictable manner.
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Berry et al. (1984) studied this question.