Tosic acid-on-silica gel: A cheap and eco-friendly catalyst for a convenient one-pot synthesis of substituted benzimidazoles

2-Substituted and 1,2-disubstited benzimidazoles were prepared efficiently from o-phenylenediamines and aryl aldehydes using p-toluenesulphonic acid (5mol%)-on-silica gel as a cheap and environmentally benign catalyst.