This study reports that the combination of Cu(II) with hydroxylamine (HA) (referred to herein as Cu(II)/HA system) in situ generates H₂O₂ by reducing dissolved oxygen, subsequently producing reactive oxidants through the reaction of Cu(I) with H₂O₂. The external supply of H₂O₂ to the Cu(II)/HA system (i.e., the Cu(II)/H₂O₂/HA system) was found to further enhance the production of reactive oxidants. Both the Cu(II)/HA and Cu(II)/H₂O₂/HA systems effectively oxidized benzoate (BA) at pH between 4 and 8, yielding a hydroxylated product, p-hydroxybenzoate (pHBA). The addition of a radical scavenger, tert-butyl alcohol, inhibited the BA oxidation in both systems. However, electron paramagnetic resonance (EPR) spectroscopy analysis indicated that •OH was not produced under either acidic or neutral pH conditions, suggesting that the alternative oxidant, cupryl ion (Cu(III)), is likely a dominant oxidant