3-methylimidazolium bromohydrogenates(I): a room-temperature ionic liquid for ether cleavage

H-1- and C-13{H-1}-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.