Synthesis of New Benzocoumaryl Oxadiazolyls as Strong Blue-Green Fluorescent Brighteners

Abstract

The benzocoumarin-3-ethylcarboxylate 2 on treatment with hydrazine hydrate at room temperature afforded benzocoumarin-3-carbohydrazide 3. The compound 3 served as key intermediate in the synthesis of the title compounds. Thus, benzocoumarin-1,3,4-oxadiazolyls 6a–e were obtained in two ways, i.e. one by direct cyclization of benzocoumarin-3- carbohydrazide 3 with substituted benzoic acids in POCl₃ and the other by cyclization of Schiff bases of compounds 5a–e in the presence of bromine/ acetic acid. The structures of the novel benzocoumaryl oxadiazolyls 6a–e were confirmed by spectral analysis. The benzocoumarin-1,3,4-oxadiazolyls 6a–e exhibited strong blue and green fluorescent properties. The Stoke’s shifts range from 43 to 165 nm. The absorption and fluorescence maxima of the benzocoumaryl oxadiazolyls showed good bathochromic shifts.

Keywords: Benzocoumarin-3-ethylcarboxylate, benzocoumaryl oxadiazolyls, fluorescent brighteners