Nitration of Phenol and Substituted Phenols with Dilute Nitric Acid Using Phase-Transfer Catalysts

Highly selective nitration of phenol and substituted phenols to the corresponding nitro compounds is accomplished under mild conditions in a liquid−liquid two-phase system with dilute nitric acid (6 wt %) and in the presence of a phase-transfer catalyst. The consequence of various phase-transfer catalysts on the reaction rate is contemplated. Tetrabutylammonium bromide (TBAB) was found to be the most effective phase-transfer catalyst in terms of conversion and selectivity. The experimental results are accounted for by a binary role of the phase-transfer catalyst in this system. It is anticipated to extract nitric acid into the organic phase via the hydrogen-bonded complex and to supply HBr, formed in situ in the reaction scheme by anion exchange, which is believed to be the key for generation of the active nitration species, nitronium ion in the organic phase.