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Oxazines as acid-base indicators. X. Some Meldola's blue derivatives

V. Stužka, V. Šimánek, and E. Ružička

Department of Organic, Analytical and Physical Chemistry, Faculty of Natural Sciences, Palacký University, Olomouc


Abstract: Certain 5-arylaminosulfo- and 5-1-naphtylaminosulfoderivatives of Meldol blue were synthetized the latter being allowed to react with alkali metal salt of arylaminosulfonic acid. All substances thus obtained were analyzed, checked by thin layer chromatography using a loose layer of silica gel in the solvent system benzene — ethanol 13 : 7. Their infra-red spectra were taken in KBr pellets and ultra-violet spectra in ethanol. The absorption of the dye salt in the visible region lies at longer wavelength, while bases absorb at shorter wavelength. Ionization constants of the studied compounds were examined in 50 % ethanol at μ = 0.05. Higher values of the ionization constants, when compared with substituents of close a values, are due to the suppression of the electronegative effect of the involved sulfo group as a result of compensation of the internal ion formation. The authors assume the a value of this type of substance as being not reproducible even for the reason that the electron density distribution in the nucleus is another in the internal ion and another one in the case, where the substituent reveals only its inductive and mesomeric effects.

Full paper in Portable Document Format: 226a431.pdf (in Czech)


Chemical Papers 22 (6) 431–438 (1968)

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