Kinetics and mechanism of oxidation of L-methionine by iron(III)-1,10-phenanthroline complex have been studied in perchloric acid medium. The reaction is first order each in iron(III) and methionine. Increase in [phenanthroline] increases the rate while increase in [HClO4] decreases it. While the reactive species of the substrate is the zwitterionic form, that of the oxidant is [Fe(phen)2(H2O)2]3+. The proposed mechanism leads to the rate law $$\frac{{d[Fe(phen)_3^{2 + } ]}}{{dt}} = \frac{{k_2 K_4 K_3 K_2^2 [Fe^{III} ][phen]^2 [Met]}}{{(1 + K_1 [H^ + ])([H^ + ]^{2 } + K_4 K_3 K_2^2 [phen]^2 )}} \cdot $$
