Silica gel-mediated microwave-assisted efficient synthesis of highly substituted imidazoles and exploration of naked eye/colorimetric sensor for anions

Ammonium formate and silica gel have been found to be efficient reagent combination for an improved and very rapid one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles in excellent yields. Multicomponent condensation in the presence of solid support with operational simplicity, inexpensive reagents, high yield of products, tolerance of sensitive functionalities, use of non-hazardous and non-toxic reagents combination under solventless condition makes this synthetic protocol, an attractive one. Moreover, trisubstituted imidazole, 2-(4,5-diphenyl-1H-imidazol-2-yl)-4-phenylazo-phenol or tetrasubstituted imidazole, 2-(4,5-diphenyl-1-thiazol-2-yl)-1H-imidazol-2-yl)-4-phenylazophenol have been found to be naked eye and colorimetric sensor for anions like F-, Cl-, CH3COO-, H2PO4- offering very high binding constant with F- ion (K = 1.39 x 10(4) M-1).