Layered double hydroxides exchanged with tungstate as biomimetic catalystsfor mild oxidative bromination

The manufacture of a range of bulk and fine chemicals, including flame reta rdants, disinfectants and antibacterial and antiviral drugs, involves bromi nation(1), Conventional bromination methods typically use elemental bromine , a pollutant and a safety and health hazard, Attempts to develop alternati ve and more benign strategies have been inspired by haloperoxidase enzymes, which achieve selective halogenation at room temperature and nearly neutra l pH by oxidizing inorganic halides with hydrogen peroxide(2,3), The enzyme vanadium bromoperoxidase has attracted particular interest(4,5) in this re gard, and several homogeneous inorganic catalysts mimicking its activity ar e available(6-11) although they are limited by the requirement for strongly acidic reaction media. A heterogenous mimic operating at neutral pH has al so been reported(12), but shows only modest catalytic activity. Here we des cribe a tungstate-exchanged layered double hydroxide that catalyses oxidati ve bromination and bromide-assisted epoxidation reactions in a selective ma nner, We find that the catalyst is over 100 times more active than its homo geneous analogue. The low cost and heterogeneous character of this system, together with its ability to operate efficiently under mild conditions usin g bromides rather than elemental bromine, raise the prospect of being able to develop a clean and efficient industrial route to brominated chemicals a nd drugs and epoxide intermediates.