Study of the spectroscopic properties and deprotonation of 6-bromo-2-naphthoic acid.

Abstract

The present work studies the UV-Vis spectroscopic properties of 6-bromo-2-naphthoic acid (BNA) dissolved in methanol, tetrahydrofuran (THF) and ethyl acetate. It has been found that there are significant differences between the emission spectra for the samples with different concentrations of BNA in methanol. Also, the analogical changes have been observed in the case of the samples of BNA in THF and ethyl acetate which have been studied immediately after preparation and 24h after preparation. It could be explained by deprotonation processes that take place in BNA. Moreover, it has been found that the anion formation process in BNA is more intensive in the case of methanol solvent in comparison with the cases of THF and ethyl acetate. This fact could be explained by the different polarity of these solvents. As methanol is characterized by higher polarity, the deprotonation is more intensive in the case of this solvent. To verify our assumption the quantum-chemical calculations have been also performed. It has been found that the enthalpy of dissociation (the bond-dissociation energy) is equal to 183.2, 200.2 and 205.4kcal/mol for BNA dissolved in methanol, THF and ethyl acetate, respectively. It explains why the deprotonation process in methanol is more intensive than in THF and ethyl acetate. Thereby, the study shows that the obtained theoretical calculations are in good agreement with the experimental results.