In the presence of chloramine T, the reaction between 2, 4-dinitrophenylhydrazine, and α-, β-naphthol in acidic solution afforded the corresponding products. α-Naphthol gave red needles, m. p. 277.5°(decomp.), which showed yellowish orange coloration (λ
max 460mμ) in acidic solution and blue coloration (λ
max 640mμ) in alkaline medium, which is reversible of having isosbestic point at 508 mμ. The elemental analysis, UV and IR spectra of the crystals are quite identical with 4-(2, 4-dinitrophenylazo)-1-naphthol which was synthesized from the reactions of α-naphthoquinone and 2, 4-dinitrophenylhydrazine or of α-naphthol and 2, 4-dinitrophenyldiazoniumsulfate. On the other hand, β-naphthol gave reddish orange needles, m. p. 305.5°(decomp.), showing orange-yellow coloration (λ
max 480mμ) in acidic solution and blue (λ
max 600mμ) in alkaline medium. This coloration is reversible of having isosbestic point at 522mμ. The elemental analysis, UV and IR spectra are identical with 1-(2, 4-dinitrophenylazo)-2-naphthol which was synthesized from β-naphthol and 2, 4-dinitrophenyldiazoniumsulfate but was not identical with 2-(2, 4-dinitrophenylazo)-1-naphthol which was synthesized from β-naphthoquinone and 2, 4-dinitrophenylhydrazine. Therefore, the products in this reaction were found to be 4-(2, 4-dinitrophenylazo)-1-naphthol in the case of α-naphthol and 1-(2, 4-dinitrophenylazo)-2-naphthol from β-naphthol.
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