Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide

摘要

The thermodynamic properties of aqueous nitroxyl (HNO) and its anion (NO~-) have been revised to show that the ground state of NO~- is triplet and that HNO in its singlet ground state has much lower acidity, pKa(~1HNO/~3NO~-) ≈ 11.4, than previously believed. These conclusions are in accord with the observed large differences between ~1HNO and ~3NO~- in their reactivities toward O_2 and NO. Laser flash photolysis was used to generate ~1HNO and ~3NO~- by photochemical cleavage of trioxodinitrate (Angeli's anion). The spin-allowed addition of ~3O_2 to ~3NO~- produced peroxynitrite with nearly diffusion-controlled rate (k = 2.7 * 10~9 M~-1 . s~-1).