Regioselective bromination of organic substrates by LDH-CO32−–Br− promoted by V2O5–H2O2
An efficient, fast, simple, mild, and selective monobromination of aromatic compounds, with high para-selectivity, is reported. The catalytic system is readily prepared from a Mg–Al-layered double hydroxide-CO32−–Br− (LDH-CO32−–Br−) as the source of bromide, V2O5 as a promoter and hydrogen peroxide as the oxidant. The use of hydrogen peroxide as a synthetically useful oxidizing agent is reported for generating electrophilic bromine in situ from easily available KBr as a bromine source, to brominate electron rich aromatic compounds, employing LDH-CO32−–Br3− as the phase-transfer catalyst. The phase-transfer catalyst leads to nearly complete bromination in 3 h at room temperature with high selectivity. The reaction rate of p-bromoanisole and p-bromotoluene formation by LDH-CO32−–Br3− in a triphasic system was studied. The heterogeneity of the reaction system facilitates the recovery and recycling of the catalyst, and the reagent components are environmentally acceptable. The catalyst, LDH-CO32−–Br3−, and its precursors, LDH-CO32−–Br− and LDH-CO32−, were characterized by powder XRD, FT-IR and UV–vis spectroscopy.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (90 K)Download as PowerPoint slideResearch highlights▶ Regioselective monobromination of aromatic compounds by hydrotalcites. ▶ New heterogeneous catalytic system for selective bromination of aromatic compounds. ▶ New method for substituting quaternary ammonium tribromides.
Journal: Applied Catalysis A: General - Volume 384, Issues 1–2, 20 August 2010, Pages 18–26