Facile cyclization of 2-arylethynyl aniline to 4(1H)-cinnolones: a new chemodosimeter for nitrite ions

2-Arylethynyl anilines undergo very fast reaction (5 min) with nitrite ions in aqueous acidic media to produce 4(1H)-cinnolones which exhibit yellow color and UV absorbance at 391 nm. This reaction is irreversible and has been successfully tested for the detection of nitrite ions in water at ppm concentration. Thus, 2-phenylethynyl aniline serves as a chemodosimeter. An efficient and general method for the synthesis of 4(1H)-cinnolones has been developed based on this reaction.