Extraction of Bromide From Seawater and Bromination of Phenol with Seawater by Bio-Mimicking Catalysis

It is now well established that the naturally occurring bromoorganic compounds in marine aquatics are the result of Vanadium BromoPeroxidase(VBrPO) activity. The VBrPO enzyme catalyzes the oxidation of bromide by hydrogen peroxide followed by bromination of the organic compounds [1]. Although the reaction mechanism of VBrPO is not fully understood, it has been proposed that an active ?bromination species' is formed in situ, which could be ?Br+', ?OBr -' or ? Br3- '. The later has been isolated serendipitously in our laboratory which has led us to develop an eco-friendly and general route to the synthesis of quaternary ammonium tribromides (QATBs) [2].Taking cues from the bromoperoxidase activity and having successful synthetic procedure of QATBs in hand, we have been able to isolate quantitatively the solid tribromide by oxidizing the MgBr2 from seawater in presence of variety of catalysts. Herein, we are reporting a novel compound, viz. DmpzH[VO(O2)2dmpz] as one of the best catalysts and the experimental procedure for the extraction of bromide from seawater has been demonstrated [3]. A Variety of tribromides like TBATB, BTMATB, CTMATB, TEATB and TMATB has been synthesized from seawater quantitatively. Further, in view of wider use of bromo-organic compounds in the synthesis of a large number of natural products as well as in the manufacture of pharmaceuticals, agrochemicals and numerous industrially valuable products, bromination of organic compounds has received significant interest in recent years. For over a century, molecular bromine has been found most commonly and widely used brominating reagent as it is inexpensive and easily available. However, this classical bromination method suffers from an inherent disadvantage of 50% atom economy along with the production of one equivalent of hazardous HBr [4].Having encouraging result with the extraction from bromide from seawater and being known that tribromide might as well be an alternative for the bromination reaction, we have achieved direct bromination of phenol with sea water without adding external bromide, where tribromide has been generated in situ. Generally, bromination of phenol leads to mixture of bromophenol products (o-, p-, di-, tri- bromophenol). However, we have been able to achieve p-bromophenol selectively with seawater after conducting several reactions in presence of the aforesaid catalyst. 1. D.C. Crans, J. J. Smee, E. Gaidamauskas, L. Yang, Chem. Rev., 2004, 849. 2. M.K.Chaudhuri, U.Bora, S.K.Dehury, M.L.Kantam, B.M.Chaudhuri, US Patent 7005548, Feb. 28, 2006. 3. S.K.Bharadwaj, M.K.Chaudhuri, Indian patent( applied for). 4. P. B. De laMare, in Electrophilic Halogenation, Cambridge University Press, Cambridge, 1976, Chapter 5.

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