Selective nitration of phenol and substituted phenols with dilute nitric acid: The role of tetrabutylammonium bromide

IEC 173

Ashutosh V. Joshi1, Mubeen Baidoosi1, Sudip Mukhopadhyay2, and Yoel Sasson1. (1) Applied Chemistry, Hebrew University, Givat Ram Campus, Jerusalem, 91904, Israel, (2) Department of Chemical Engineering, University of California at Berkeley, CA 94720, Berkeley, CA 94720
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 effect of various phase-transfer catalysts on the rate of reaction is examined. Tetrabutylammonium bromide (TBAB) has shown high catalytic activity in terms of conversion and selectivity. Tetrabutylammonium chloride (TBAC) is less active and Tetrabutylammonium iodide (TBAI) is not active. The experimental results support a binary role of TBAB in this system. Presumably it extracts nitric acid into the organic phase via hydrogen bonded complex and also generates HBr, formed in situ in the reaction mixture by anion exchange.