A general synthetic route to benzo[d]imidazoles has been developed using 1,4-diazabicyclo [2.2.2] octanium diacetate as a new bis ionic liquid under thermal and solvent free condition. The union of two fragments including one equivalent of various aldehydes and one equivalent of 1,2-phenylenediamine was accomplished by an efficient and convenient protocol enabling the synthesis of benzo[d]imidazoles in excellent yields. The major advantages of the present method are: less reaction times, high yields, and easy purification of the products, solvent-free conditions, environmental friendliness, and convenient operation.