Pulse radiolytic investigations of OHCH₂O₂ radicals

Methanol radicals CH₂OH react with oxygen and produce peroxy radicals O₂CH₂OH, k_H2OH+O2 = (4.2 ± 0.5) × 10⁹ M^-1 sec^-1. O₂CH₂OH ionizes to form O₂CH₂O^- which quickly decomposes to CH₂O and O₂^-. The ionization is catalyzed by OH^- and by HPO₄^2-. k_O2CH2OH+OH- = (1-8 ± 0.9) × 10¹⁰ M^-1 sec^-1 and k_{O2CH2OH+HPO42-} ≃ 2 × 10⁶ M^-1 sec^-1 were measured. The spontaneous ionization rate constant k_{O2CH2OH→O2CH2O-+H+} < 3 sec^-1 was estimated. The pK of O₂CH₂OH was estimated to be higher than 6, and probably >8.8. Previous reports of more accurate determinations of pK values of peroxy radicals should be reconsidered, in view of the possible instability of the basic form of the peroxy radicals. The absorption spectrum of O₂CH₂OH was determined, ε 1070 M^-1 cm^-1 was measured at 248 nm. At relatively high pulse intensities, formation of O₂^- from O₂CH₂OH is inhibited, and a second-order process which competes with the unimolecular formation of O₂^- from O₂CH₂O^- is proposed.