Abstract
Action of bromine in concentrated nitric acid allows carrying out mono- and polybromination of moderately deactivated aromatic compounds. 4-Chloronitrobenzene and isophthalic acid turnes into 3-bromo-4-chloronitrobenzene and 5-bromoisophthalic acid at reaction with bromine in concentrated nitric acid at 20°C whereas in absence of bromine in the same conditions 4-chloro-1, 3-dinitrobenzene and 5-nitroisophthalic acid are formed accordingly. Presence of bromine in concentrated nitric acid changes nitrating capacity to brominating one. Terephthalic acid and phthalic anhydride at heating with bromine in concentrated nitric acid can be transformed to appropriating tetrabromo substituted compounds.
Highlights
Aromatic compounds with bromine atom in the ring are of great value in organic chemistry
Earlier we have described bromination of strongly deactivated aromatic compounds by action of bromine in concentrated sulfuric acid in the presence of nitric acid [2] and have discussed competition of bromination and nitration in this media [3]
Content of nitronium cation in pure nitric acid observed by Raman and IR spectra is about several percents (~3% molar) owing to self-dehydration: 2HNO3 + NO2+ NO3− + H2O, and it strongly decreases with the addition of 5% water [8]
Summary
Aromatic compounds with bromine atom in the ring are of great value in organic chemistry. The principal method of bromine introduction into aromatic molecules is electrophilic bromination It proceeds when activating electron-donating substituents are present in the ring but when deactivating electron-withdrawing substituents are present special methods are required [1]. (2014) Aromatic Bromination in Concentrated Nitric Acid. Earlier we have described bromination of strongly deactivated aromatic compounds by action of bromine in concentrated sulfuric acid in the presence of nitric acid [2] and have discussed competition of bromination and nitration in this media [3]. It has appeared that moderately deactivated aromatic compounds which are nitrated with concentrated nitric acid are only brominated if concentrated nitric acid contains bromine. Possibility to use treatment with bromine in concentrated nitric acid for synthesis mono- and polybromo substituted aromatics is considered in the present work
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