5982
Intermediates Produced from the One-Electron Oxidation and Reduction of Hydroxylamines. Acid-Base Properties of the Amino, Hydroxyamino, and Methoxyamino Radicals M. Simic' and E. Hayon*
Contribution from the Pioneering Research Laboratory, U.S.Army Natick Laboratories, Natick, Massachusetts 01760. Received March 8, 1971 Abstract: The optical absorption spectra of the intermediates produced from the one-electron oxidation and reduction of hydroxylamines were observed using the technique of pulse radiolysis. The hydroxyl radicals produced from the radiolysis of water were found to react much faster with the unprotonated hydroxylamines as compared to the protonatedform: k(OH NfH30H) 5.0 X los M-' sec-l, k(OH NH20H) = 9.5 X lo9M - l ~ e c - ~ .The intermediate produced has an absorption maximum at 217 nm, €217 2.5 x IO3M-1 cm-1, and decays by second-order kinetics, 2k = 4.5 =k 2.0 X lo8M-l sec-I. This spectrum is assigned to the hydroxylamino radical 'NHOH. From an examination of its acid-base properties, a pK(.N+H20H$ .NHOH H+) = 4.2 i 0.1 was obtained. A similar examination of the one-electron oxidation of 0-methylhydroxylamine shows A,, 218 nm, tZl81.4 X IO3 M-1 cm-l, 2k = 1.4 X IO9M-lcm-1 , and pK(, N+H20CH32 NHOCH3 H+) = 2.9 i 0.2. One-electron reduction of hydroxylamine by hydrated electrons showed a dependence on the state of protonation of the molecule: k(easN+H30H) = 1.2 X 1Olo M-l sec-' and &e,,NH20H) = 9.2 X lo8 M-1 sec-'. The intermediate produced is the ammonium radical cation, eaq- N+H30H -., .NHaf OH-, and its adduct to benzene to give the N H ~ C ~ radical HC has A,, 310 nm and 6310 7400 M-I cm-l. A similar reaction takes place with O-methylhydroxylamine. From its pH dependence on reaction with thiocyanate ions, the dissociation constant of the ammoniumradicalcation wasobtained, pK(.NH$+e .NH2 H+) = 6.7 i. 0.2. The properties of this radical are discussed.
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