Cytochrome P-450 model reaction: effects of substitution on the rate of aromatic hydroxylation

The study of haemin-catalysed oxidation reactions was extended to substitut ed aromatic rings. Both electron-donating and electron-withdrawing substitu ents on aromatic rings act as para- and meta-directing agents in the presen ce of tetrakis(2,6-dichlorophenyl)porphyrin iron(LII) chloride as catalyst and m-chloroperbenzoic acid as oxidant. A new kinetic method for measuring relative rates of epoxidation of alkenes and related compounds has been dev eloped; while steric hindrance results in decreasing the rate of hydroxylat ion, electron-rich and electron-withdrawing substituents were found to incr ease the rate of hydroxylation, A linear relationship between the logarithm of the relative rate of hydroxylation and sigma Hammet is obtained, althou gh electron-donating and electron-withdrawing substituents fit separate lin es. Addition of pyridine to haemin was shown to increase the yield of epoxi dation but decrease the yield of aromatic hydroxylation. Copyright (C) 2000 John Wiley & Sons, Ltd.