REACTION OF 5,5-DIMETHYL-1-PYRROLINE 1-OXIDE WITH HYPOCHLORITE-TREATED AMMONIA - THE STRUCTURE OF A NOVEL N-CHLOROIMINE NITROXYL RADICAL

A novel nitroxyl radical was observed by electron paramagnetic resonance spectroscopy (EPR) of reaction mixtures containing ammonium ion, hypochlorous acid (HOCl), and 5,5-dimethyl-1-pyrroline 1-oxide (DMPO). The structure of this radical was established as 2-(N-chloroimino)-5,5-dimethylpyrrolidine-1-oxyl on the basis of EPR studies of isotopically-labeled compounds, thin-layer chromatography (TLC), and chemical synthesis by an independent route. Incorporation of deuterium into DMPO and solvent stabilized the radical without affecting the multiplicity of the EPR signal. The use of [N-15]ammonium ion gave 2-(N-15-chloroimino)-5,5-dimethylpyrrolidine-1-oxyl radical. Detection of the radical upon TLC was based on its reaction with potassium iodide-starch to give a purple color, consistent with an N-chloroimine functionality. Synthesis of the new nitroxyl radical was accomplished by the Michael reaction of acrylonitrile and 2-nitropropane, catalytic hydrogenation of the Michael product, and reaction of the reduced compound with HOCl. The formation and EPR detection of 2-(N-chloroimino)-5,5-dimethylpyrrolidine-1-oxyl radical may be useful as a sensitive method for detecting hypochlorous acid and ammonium ion in biological systems.