1‐(4‐Bromobutyl)‐3‐methyl‐imidazolium Bromide: A Novel Green Ionic Liquid Catalyst for Intermolecular Dehydration of Alcohols

Abstract A series of novel halogen‐functionalized imidazolium halides were successfully designed and synthesized by grafting halogenated hydrocarbons on the side chain of imidazolium and were applied to catalyze the intermolecular dehydration of alcohols. Under metal‐free, acid‐free, solvent‐free, mild conditions and in an air atmosphere, 1‐(4‐bromobutyl)‐3‐methylimidazolium bromide was found to efficiently catalyze the etherification of monohydric alcohols and diols, as well as the synthesis of certain unsymmetrical ethers. Interestingly, the immiscibility between ethers and ionic liquids resulted in the spontaneous separation of the catalyst from the product, which made this strategy highly applicable in the etherification. Furthermore, detailed mechanistic studies revealed that [BBrmim]Br formed a unique intermediate with a series of alcohol molecules, in which internal hydrogen atoms successfully underwent hydrogen transfer via hydrogen bonding, thereby ensuring a smooth catalytic process.