The tripotassium salt of tris(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl)methyl radical (3 K⁺ TSPTM³⁻) reacts in water with hydroxyl radical very fast with a rate constant (k = 2.4 × 10¹¹ M⁻¹ s⁻¹) much higher than that of the reaction of hydroxyl radical with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (k = 3.4 × 10⁹ M⁻¹ s⁻¹). The reaction affects the radical character of the molecule and is monitored by electron paramagnetic resonance (EPR). The hydroxyl radical scavenging is established by the characterization of the resulting water-soluble product as the dipotassium salt of 4-[bis(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl)methylene]-2,3,5,6-tetrachlorocyclohexa-2,5-dien-1-one (2).