1,3-Disulfonic acid imidazolium hydrogen sulfate {[Dsim]HSO4} as a highly efficient, recyclable and green catalyst for the preparation of α,α´-bis(arylidene)cycloalkanones

A highly efficient and simple method for the preparation of α,α´-bis(arylidene)cycloalkanones under solvent-free conditions has been developed. The crossed-aldol condensation of cycloalkanones (1 eq.) with arylaldehydes (2 eq.) in the presence of 2.5 mol% of ionic liquid 1,3-disulfonic acid imidazolium hydrogen sulfate {[Dsim]HSO4} afforded the title compounds in high yields and short reaction times. The catalyst has dual-functions and it is so because of possessing three acidic functional groups with different Brønsted acidic and basic sites. High catalytic activity and low loading of the catalyst can be attributed to its dual-functions. The promising points for the presented protocol are simple and clean reaction profile, efficiency, generality, low catalyst loading, high yields, performing the reaction in solvent-free media without side reactions, non-toxicity as well as low cost of the catalyst, and good compliance with the green chemistry protocols, which makes it an attractive procedure for the synthesis of α,α´-bis(arylidene)cycloalkanones as an important class of organic compounds.