5690-27-7Relevant academic research and scientific papers
Thermodynamics of semiquinone disproportionation in aqueous buffer
Alegria, Antonio E.,Lopez, Marcos,Guevara, Norberto
, p. 4965 - 4968 (2007/10/03)
The thermodynamic parameters, Kdisp, ΔH° and ΔS°, controlling the disproportionation of semiquinones derived from 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 2-methylbenzoquinone (MBQ), menadione (MNQ), naphthazarin (NZQ) and quinizarin (QNZ), have been determined. Smaller disproportionation constants, Kdisp, are observed upon addition of a fused benzene ring to the semiquinone structure. Negative enthalpies and positive entropies of disproportionation govern the disproportionation equilibria. Addition of OH groups to the 5 and 8 positions in NQ?- displaces the disproportionation equilibrium to the semiquinone probably due to intramolecular hydrogen bonding.
Reduction of the Naphthazarin Molecule as Studied by Pulse Radiolysis Part 2. - Second One-electron Step
Land, Edward J.,Mukherjee, Tulsi,Swallow, A. John,Bruce, J. Malcolm
, p. 405 - 416 (2007/10/02)
The disproportionation of the radicals formed by one-electron reduction of naphthtazarin has been observed as a function of pH in the range 1-14.The radicals are least prone to disproportionate at pH 8-9, the stability constant at pH ca. 8.5 being 0.4.The data have been combined with the one-electron reduction potentials of naphthazarin to obtain the one-electron reduction potentials of the radicals (i.e. the second one electron reduction potential of the parent) as a function of pH.E17 of the radicals is equal to E27 of the parent and is -15 mV.The two-electron reduction potential of naphthazarin is -62 mV at pH7 and -351 mV at pH 0.The optical absorption spectra of 1,4,5,8-tetrahydroxynaphthalene prepared in different ionised forms by radiolysis and by chemical reduction have been determined.The redox data and the absorption spectra show that this compound has pKa values of 7.6 and 8.7 and has no further pKa values below ca. 14.
