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Updated: Oct 17, 2026

Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores
Published on: August 19, 2013
[Color reactions for identification of nalidixic acid]
K Görlitzer1, G Badia, P G Jones
1Institut für Pharmazeutische Chemie, Technischen Universität Braunschweig, Germany. k.goerlitzer@tu-bs.de
Abstract:
Nalidixic acid (1) gives with 2-naphthol a yellow charge-transfer complex. The 7-methyl group of 1 condenses with vanillin (2) and Ehrlich's reagent (4) to the coloured (E)-benzylidene compounds 3 and 5. Treating 1 with thionyl chloride and subsequent reaction with aminopyrazolone (6) and sodium acetate leads to a mixture of trichloronalidixic acid (7) and its 3-carboxamide 8. The trichloromethyl group of 7 is converted with 6 in pyridine to form the amide 9. Nalidixic acid reacts with 1,3-dimethylbarbituric acid (10) in acetanhydride/acetic acid to yield the polymethine dyes 11-13, whose structures are confirmed by X-ray crystal structure analysis. The dyes 3 and 12 inhibit the growth of staphylococcus aureus and Escherichia coli, respectively.
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