Revisiting tetranitrophenolsulfonephthalein |
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| Authors: | Nikolay O. Mchedlov‐Petrossyan Kateryna V. Roshchyna Sergey V. Shekhovtsov Sergey V. Eltsov Oleksii S. Zozulia Irina V. Omelchenko Oleg V. Shishkin |
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| Affiliation: | 1. Department of Physical Chemistry, Kharkov V Karazin National University, Kharkov, Ukraine;2. Department of Chemistry and Pharmacy, Friedrich‐Alexander University, Erlangen–Nürnberg, Germany;3. Institute for Single Crystals (SSI), Division of Functional Materials Chemistry, National Academy of Sciences of Ukraine, Kharkov, Ukraine |
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| Abstract: | Among the vast series of phenolsulfonephthalein dyes, the nitro derivatives and especially 3,3′,5,5′‐tetranitrophenolsulfonephthalein (nitrophenol crimson) remain practically unexplored, whereas the halogen and alkyl derivatives have been studied comprehensively. This striking difference is probably due to the enormous influence of the four NO2 groups on the properties of the dye. As a result, the protolytic behaviour is unlike even that of tetrabromo phenolsulfonephthalein, and the recognised scheme of acid–base and tautomeric equilibrium of the sulfonephthaleins is unable to explain it. The molecular form H2R was isolated as a sultonic tautomer, and an X‐ray crystal structure analysis was carried out. Our studies of the UV‐vis absorption spectra in water, methanol, dimethyl sulfoxide, acetonitrile, acetone, and dichloromethane, as well as in aqueous micellar solutions of surfactants, allowed us to evaluate the true molar absorptivity of the dianion R2?, and to elucidate the enormous tendency to form yellow trianionic carbinol ROH3?, even in the presence of traces of H2O. Nuclear magnetic resonance and electrospray data confirm the proposed scheme of ionisation and tautomerism of nitrophenol crimson. |
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