OXIDATIVE COUPLING OF PHENOLS AND ANILINES BY PEROXIDASE - STRUCTURE-ACTIVITY-RELATIONSHIPS

The relationship between molecular structure and reactivity for the peroxidase mediated coupling of substituted anilines and phenols was studied 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. Good correlation was found between electron donor rate constants and their respective Hammett substituent .sigma.+ constants, which indicated the formation of a positively charged transition state as the rate controlling step. The .rho. 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. The reaction rates probably depended on electron density at the reaction center (-NH2 or -OH) in a predictable manner.