Design, characterization, and use of N,N-diethyl-N-sulfoethanaminium hydrogen sulfate {[Et3N-SO3H]HSO4} as a novel and highly efficient catalyst for preparation of α,α′-bis(arylidene)cycloalkanones

The aim of this work is to introduce a novel and attractive protic acidic ionic liquid as catalyst for organic synthesis. To achieve this aim, N,N-diethyl-N-sulfoethanaminium hydrogen sulfate {[Et3N-SO3H]HSO4} was prepared by reaction of NEt3 with ClSO3H and then with H2SO4. The novel acidic ionic liquid was identified by Fourier-transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), 13C NMR, and mass spectroscopies. Its catalytic activity was then examined in the cross-aldol condensation reaction of arylaldehydes with cycloalkanones under solvent-free conditions, obtaining α,α′-bis(arylidene)cycloalkanones in high yield after short reaction time.