Oxidation of thiocyanate by iron(V) in alkaline medium

The oxidation of thiocyanate by iron(V) (Fe(V)) was studied as a function of pH in alkaline solutions by a premix pulse radiolysis technique. The rates decrease with an increase in pH. The rate law for the oxidation of SCN− by Fe(V) was obtained as −d[Fe(V)]/dt = k10{[H+]2/([H+]2 + K2[H+] + K2K3)}[Fe(V)][SCN−], where k10 = 5.72 ± 0.19 × 106 M−1 s−1, pK2 = 7.2, and pK3 = 10.1. The reaction precedes via a two-electron oxidation, which converts Fe(V) to Fe(III). Thiocyanate reacts approximately 103× faster with iron(V) than does with iron(VI).