Imidazole 1-oxides proton exchange

Protons at C2 of imidazole 1-oxides 228 are acidic and are exchanged with deuterium even in weakly acidic solution. The exchange rate increases with increasing pH (2004S2678). Although the mechanism is not fully understood, the palladium-catalyzed direct arylation of imidazole 1-oxides most likely involves deprotonation so that the observed regi-oselective arylation reflects the propensity to proton abstraction found to decrease in the order C2 > C5 > C4 (2009JA3291). 

Although protons at C2 of imidazole 1-oxides 228 are fairly acidic as shown by their facile exchange with deuterium in deuterium oxide solution (2004S2678), subsequent trapping of the anion with electrophiles has not been exploited. 

In 2002, Goward et al. carried out the first study of proton conductivity using the high-resolution solid-state MAS NMR [25], They characterized the ethylene oxide tethered imidazole heterocycles by variable temperature experiments, as well as 2D homonuclear DQ NMR and 2D exchange spectroscopy (EXSY). The MAS NMR identified three types of hydrogen-bonded N—resonances, and DQ NMR identified hydrogen-bonded protons which are mobile on the time scale of the experiment and participate in proton transport. The local mobifity of protons was characterized by spin—spin relaxation times as a function of temperature,... 

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