3-Hydroxy imidazole 1-oxides alkylation

One of the common properties of imidazole N-oxides is their strong association even in dilute solution, and in the solid state such association can mask distinction in the IR between NH and OH bands. Thus IR studies of such compounds in the solid state may give rise to confusing results. Careful UV studies of 1-hydroxybenzimidazoles show that with a variety of substituents (e.g. 6-nitro, 2-alkyl or 2-aryl) the hydroxy form (73) is favoured in organic solvents, and the more polar oxide form (74) in water (there is a mixture of both in aqueous ethanol). With 1-hydroxybenzimidazole the N-methyl model (75) is not sterically hindered, and the value of Kt (74173) = 12 deduced from the pK values of the models (75/76) in water should be much more reliable than that for the hydroxyimidazoles (Scheme 24). In other solvents (benzene, chloroform, acetonitrile, dioxane), UV results show that the OH form (73) predominates in 75% aqueous ethanol Kt=1. 

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