Stability of Imidazoline Nitroxides in Acid Media

Most of the nitroxides containing functional groups undergo disproportionation to oxoammonium and hydroxyammonium cations in 

The disproportionation reaction proceeds both in aqueous and nonaqueous solvents and is catalyzed by hydroxonium ions (specific acid catalysis) and by molecules of nondissociated acids (general acid 

Nitroxides of the imidazoline series, however, proved to be stable in acid media. Thus, 3-imidazoline-3-oxide-l-oxyl 7c and 3-imidazoline-l-oxyl 13c are soluble in concentrated aqueous acids and give paramagnetic, orange-colored solutions (Golubev et al., 1974). Dilution of the freshly prepared solutions with water results in quantitative regeneration of the 

Nitroxides of this type are also stable to triethyloxonium salts. Thus, the interaction of nitroxide 7c with triethyloxonium tetrafluoroborate 

Compounds 21-23 are cation-radical salts in which the unpaired electron and positive charge are localized on different functional groups. These salts are yellow or orange crystalline substances that decompose at their melting points. Colored solutions of these salts become gradually decolorized, and diamagnetic decomposition products are formed. When salts 21 and 22 are treated with water, they become hydrolyzed to the 

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