Silica-supported quinolinium tribromide: a recoverable solid brominating reagent for regioselective monobromination of aromatic amines

Zheng Li,Xiunan Sun,Lue Wang,Yuanhong Ma,Yanbo Li

doi:10.1590/s0103-50532010000300015

Abstract

Silica-supported quinolinium tribromide was synthesized and found to be an efficient, stable, and recoverable solid brominating reagent for the regioselective monobromination of aromatic amines. This protocol has advantages of high yield, mild condition and simple work-up procedure.

Highlights

Bromination of aromatic substrates has received significant interest in recent years due to the increasing commercial importance of bromo-organics in the synthesis of a large number of natural products as well as in the manufacture of pharmaceuticals, agrochemicals and other specialty chemicals
In continuation of our study on the chemical transformation using silica-supported reagent, in this paper, we report a new bromination method which uses silica-supported quinolinium tribromide (SQTB) instead of liquid bromine as an alternative electrophilic bromine source to deliver a stoichiometric amount of bromine to aromatic amines and regioselectively synthesize monobromination products under mild condition
The resulting mixture was filtered to recover the spent silica-supported quinolinium tribromide, which was washed by CH2Cl2 (3×10 mL) and regenerated by further reaction with hydrobromic acid and sodium bromated

Summary

Introduction

Bromination of aromatic substrates has received significant interest in recent years due to the increasing commercial importance of bromo-organics in the synthesis of a large number of natural products as well as in the manufacture of pharmaceuticals, agrochemicals and other specialty chemicals. A variety of new methods for the bromination of aromatic compounds have been reported in the literature ranging from NBS,[4] KBr/mineral acid,[5]. In continuation of our study on the chemical transformation using silica-supported reagent, in this paper, we report a new bromination method which uses silica-supported quinolinium tribromide (SQTB) instead of liquid bromine as an alternative electrophilic bromine source to deliver a stoichiometric amount of bromine to aromatic amines and regioselectively synthesize monobromination products under mild condition. The course of reaction and purity of products were checked by TLC

Preparation of silica chloride

Results and Discussion

Reaction condition