Synthesis of substituted trisphenols by use of a double acidic ionic liquid under solvent-free conditions

3-methyl-1-(4-sulfobutyl)-1-H-imidazol-3ium hydrogen sulfate, as a dual acidic ionic liquid (DAIL), was found to be an efficient catalyst for the simple, rapid and green synthesis of substituted trisphenols from the condensation of different substituted phenols and 2,6-bis (methylol) phenols (BMP). DAIL catalyst efficiently promoted the reaction between phenols and BMPs with a variety of functionalities. Use of a non-corrosive and reusable catalyst, high yields of the products, short reaction times and solvent-free conditions are as worthwhile advantages of the present method.