Kreuzkonjugierte Cyanine und Merocyanine aus Salzen 1‐substituierter 2,3‐Dimethylchinoxaline. 3. Mitteilung. Über die Indikatoreigenschaften der Farbbasen und die Tautomerie der konjugaten Farbsäuren

Abstract

UV./VIS. and 'H-NMR. spectra of the indicator bases 1 in acidic solutions are presented. The solutions of the dye acids N and NN' (Scheme 2) are in general not stable due to tautomerism. The relative pKa-values are set in relation to data of equilibria and half-life periods. The latter ones depend on the substituents and on the acidity of the solutions. An inverse substituent effect observed in protic solvents is ascribed to solvolytic reactions.The dye base 1 S (X = S03Na, R = C6H5) was synthesized starting with chlorobenzene. The cyanines 2 were obtained on treatment of 1 with HC104 in CH3CN; solutions of 1 in H2S04, however, yielded on dilution tautomeric salts that were isolated as the uerchlorates 3.