3-Methylimidazolium bromohydrogenates(i): a room-temperature ionic liquid for ether cleavage

Abstract

¹ H- and ¹³C{¹H}-NMR indicate that the liquid formed at room temperature from 1 mole of 1-methylimidazole and 2 moles of anhydrous HBr contains the 3-methylimidazolium cation (Hmim⁺) and an equilibrium anionic mixture of Br⁻, HBr₂⁻, and H₂Br₃⁻. This liquid cleaves ethers efficiently, producing the corresponding bromides and alcohols from cyclic and straight-chain dialkyl ethers and phenols and alkyl bromides from aryl alkyl ethers. During the course of the reaction, the single anion proton signal moves several ppm downfield as the [HBr₂]/[H₂Br₃⁻] ratio increases. The nitrogenic proton of Hmim⁺ is unaffected, confirming that it is not labile and nor is it involved in the reaction, in accord with the large proton affinity of 1-methylimidazole.