At [H+] = 0.04 mol dm-3, μ = 0.25 mol dm-3 (NaClO4), T = 31.0 ± 1.0oC and λ = 670 nm, the bridging superoxide in [(NH3)5Co(O2)Co(NH3)5]Cl5.H2O, herein refer to as Co(O2)Co5+, quantitatively oxidizes 1-methyl-2-thiourea (MTU) to the corresponding urea derivative, itself being reduced to molecular oxygen and Co(II) in aqueous perchloric acid. The reaction obeys the empirical rate law:

-d[Co(O2)Co5+]/dt = k2[Co(O2)Co5+][MTU]

with k2 = (2.65 ± 0.15) x 10-2 dm3 mol-1 s-1. The rate of the reaction increased with increase in ionic strength of reaction medium. There is no evidence for the formation of an intermediate complex of significant stability and free radicals are not detected in the reaction. Added anions catalyzed the reaction. Based on the experimental data obtained, the outer-sphere mechanism is proposed.