Identification tests of nalidixic acid by colour reactions

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 thion yl chloride and subsequent reaction with aminopyrazolone (6) and sodium ace tate leads to a mixture of trichloronalidixic acid (7) and its 3-carboxamid e 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) i n acetanhydride/acetic acid to yield the polymethine dyes 11-13, whose stru ctures are confirmed by X-ray crystal structure analyses. The dyes 3 and 12 inhibit the growth of staphylococcus aureus and Escherichia coli, respecti vely.