A mild, efficient, and ecofriendly procedure for cyclotrimerization of aldehydes was realized by using a series of novel Brønsted acidic ionic liquids (BAILs) consisting of double–SO 3 H groups in cations as catalysts. Good conversion of aldehydes and selectivity of trialkyl-1,3,5-trioxanes were achieved by using 1 mol% of BAILs. In addition, the catalyst system could be recycled and reused at least eight times without apparent loss of activity. ... A mild, efficient, and ...
