MECHANISTIC STUDIES BY ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY ON THE FORMATION OF 2-(N-CHLOROIMINO)-5,5-DIMETHYLPYRROLIDIN RADICAL FROM 5,5-DIMETHYL-1-PYRROLINE 1-OXIDE AND HYPOCHLORITE-TREATED AMMONIA

Mixtures of ammonium ion (NH4+) or ammonia (NH3), hypochlorous acid (H OCl), and 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) gave the radical 2-( N-chloroimino)-5,5-dimethylpyrrolidin-1-oxyl (1). The first step in th e formation of 1 was the reaction of HOCl and NH4+ to provide ammonia chloramines: monochloramine (NH2Cl), dichloramine (NHC2), and trichlor amine (NCl3). Chloramine composition and the formation of 1 were depen dent on pH, the ratio of NH4+ to HOCl, and, at acidic pH, on the conce ntration of chloride in the medium. Conditions were chosen to isolate the individual chloramines in solution for further study. NCl3 and DMP O gave 1; however, NHCl2 and NH2Cl required additional oxidants such a s HOCl or PbO2 to produce 1. Studies with N-15-labeled chloramines con firmed that NHCl2 and NH2Cl reacted with DMPO to form N-chloro interme diates that yielded 1 upon subsequent oxidation. Light had no effect o n the formation of 1, and UV irradiation did not enhance the EPR signa l intensity but caused rapid decay, indicating that radical intermedia tes of ammonia chloramines were not involved. The mechanism of formati on of 1 appeared to involve temporary attachment of chloramine Cl to t he nitroxide oxygen of DMPO which activated its beta-carbon for nucleo philic addition of the chloramine N. SubsequentN-chlorination and/or d ehydrochlorination, depending on the reactive chloramine, would then p rovide 1. However, nucleophilic addition of H2O to the activated beta- carbon of DMPO was competitive because 5,5-dimethyl-2-hydroxypyrrolidi ne-1-oxyl (DMPO-OH) or 5,5-dimethyl-2-pyrrolidone-1-oxyl(DMPOX) radica ls were sometimes observed as minor products along with 1. Analogous c hloroimine radicals were not obtained from the reaction of ammonia chl oramines with 3,3,4,4-tetramethyl-1-pyrroline 1-oxide (M(4)PO) and N-t ert-butyl-alpha-phenylnitrone (PBN), although their 2-oxo nitroxyl der ivatives and hydroxyl adducts were formed as radical products suggesti ng that nucleophilic addition of H2O was dominant with these nitroxide s.