Synthesis, structure and acid-base behaviour of some 4-hydroxycoumarin derivatives

Abstract

The compound 3,3′-[(4-hydroxy-3-methoxy-5-nitrophenyl)methylene]- bis(4-hydroxy-2H-1-benzopyran-2-one) (1) crystallizes in the monoclinic system, space group P21/n, with cell constants a = 16.859(4), b = 6.1624(15), c = 25.164(4) Å, β = 98.019(19)°. The two 4-hydroxycoumarin fragments are intramolecularly hydrogen-bonded between hydroxyl and carbonyl groups. The pH-dependent color changes of 4-hydroxycoumarin derivatives were studied by means of potentiometric and spectrophotometric titration. On the basis of the results obtained, the use of 3,3′-[(4-hydroxy-3-methoxy-5- nitrophenyl)methylene]-bis(4-hydroxy-2H-1-benzopyran-2-one) as an indicator in alkalimetry and acidimetry is proposed. © 2007 Verlag der Zeitschrift für Naturforschung.