Abstract
Attempts at direct bromination of 1,3-di-methyl-imidazolium salts were futile. The title compounds, 2-bromo-1,3-di-methyl-imidazolium iodide chloro-form 0.33-solvate, C5H8BrN2+·I-·0.33CHCl3, 2-bromo-1,3-di-methyl-imidazolium iodide di-chloro-methane hemisolvate, C5H8BrN2+·I-·0.5CH2Cl2, and 2-bromo-1,3-di-methyl-imidazolium iodide hemi(diiodide), C5H8BrN2+·I-·0.5I2, were obtained by methyl-ation of 2-bromo-1-methyl-imidazole. They crystallized as CHCl3, CH2Cl2 or I2 solvates/adducts. The Br atom acts as a σ-hole to accept short C-Br⋯I inter-actions. C-H⋯I hydrogen bonds are observed in each structure.
Highlights
Attempts at direct bromination of 1,3-dimethylimidazolium salts were futile
C—HÁ Á ÁI hydrogen bonds are observed in each structure
Though direct bromination of the quaternary salt did not yield the desired product, it was discovered that an altered sequence of reaction was successful
Summary
Salts containing 2-bromo-1,3-dimethylimidazolium (C5H8N2Br+) cations are the objective of this work. They are presumed to be valuable precursors for substitution reactions. Since brominations in the 1,3-dimethoxyimidazolium series (Laus et al, 2007) and bromination of 1-hydroxyimidazole-3-oxide (Laus et al, 2012) gave the respective 2bromo derivatives, we hoped that in the present case bromination would yield the desired 2-bromoimidazolium salts. Though direct bromination of the quaternary salt did not yield the desired product, it was discovered that an altered sequence of reaction was successful. The reaction between the 2-lithio derivative of 1-methylimidazole and an equimolar amount of CBr4 (Boga et al, 2000) or Br2 (El Borai et al, 1981) gave 2-bromo-1methylimidazole in good yield, followed by methylation using MeI to afford the desired quaternary salt as an iodide. That the elusive title cation has been secured, further modifications are envisioned, giving access to a plethora of new 2-substituted imidazolium derivatives
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