Bromine source

Tetrabromocyclohexa-2,5-dienone is also a useful bromine source. 

In 2003, Kulkarni and coworkers presented a method for the -selective oxybromi-nation of a variety of substituted phenols employing a novel heterogeneous catalytic system, the CrZSM-5 as catalyst, H2O2 as oxidant and KBr as bromine source ". Next to CrZSM-5 also other zeolites have been tested as catalysts, but although MoZSM-5 showed the highest conversion after 5 hours (89%), para-selectivity was lower (para 36% ortho 31% dibromination 22%) than observed with the CrZSM-5 material (83%... 

The initial study on the MeO-TEMPO / Mg(N03)2 / NBS triple catalyst system in the oxidation of 1 indicated the necessity of all three components the TEMPO based catalyst, the nitrate source (MNT) and the bromine source (NBS). A large number of metal nitrates and nitrites were screened initially and the highest activity and aldehyde selectivity under comparable reaction conditions were recorded using Mg(N03)2 as the nitrate component. A number of organic and inorganic bromides soluble in HOAc were also screened and high reaction rates were found when NBS was used as the bromide source. The effect of the concentration of the individual components of the new triple catalyst system on the reaction rate, on the conversion of 1 and on the selectivity to 2 over 60 min reaction time is shown in Figure 1. 

Goodwin KD, North WJ, Lidstrom ME (1997) Production of Bromoform and Dibromo-methane by Giant Kelp Factors Affecting Release and Comparison to Anthropogenic Bromine Sources. Limnol Oceanogr 42 1725... 

To generate the title bromo allene 1 the -enyne was treated with a bromine cation. According to a procedure described by Murai the reagent 2,4,4,6-tetrabromocyclohexadienone (TBCO) 67 is used as the bromine source.20... 

There is a need for kinetic data on reactions and on emission strengths of the different bromine source compounds in order to be able to better estimate the BrO concentrations. Such information is needed before further conclusions can be made concerning the influence of the BrO + DMS reaction on chemical processes in the marine atmosphere. 

In ocean water, where the concentration of bromine is relatively dilute, air has proved to be the most economical blowing-out agent. However, in the treatment of relatively rich bromine sources such as brines, steaming out the bromine vapor is more satisfactory. 

For efficient allylic bromination, a large concentration of bromine must be avoided because bromine can also add to the double bond (Chapter 8). A-Bromosuccimnude (NBS) is often used as the bromine source in free-radical brominations because it combines with the HBr side product to regenerate a constant low concentration of bromine. No additional bromine is needed because most samples of NBS contain traces of Br2 to initiate the reaction. 

Simply adding bromine might raise the concentration too high, resulting in ionic addition of bromine across the double bond. A convenient bromine source for allylic bromination is A-bromosuccinimide (NBS), a brominated derivative of succinimide. Succinimide is a cyclic imide (diamide) of the four-carbon diacid succinic acid. 

Reaction of the radical intermediates with a bromine source leads to a mixture of products ... 

The importance of CHBrs as source for bromine in the free troposphere is difficult to estimate because of the scarce field data and uncertainties regarding the fate of the breakdown products. Assuming an average mixing ratio of 0.5 pmol mol" a lifetime of four weeks and that two bromine atoms are released, the bromine source would be —30% of that of CH3Br. 

Goodwin K. D., North W. J., and Lidstrom M. E. (1997) Production of bromoform and dibromomethane by Giant Kelp factors affecting release and comparison to anthropogenic bromine sources. Limnol. Oceanogr. 42, 1725-1734. 

An original modification of the Sharpless AA reaction using excess of N-bromoacetamide as nitrogen/bromine source appeared particularly useful method for the transformation of 2-aryl-vinylphosphonates (338) into syn-2-aryl-2-amino-l-bromoethyl phosphonates (339) (Scheme 91). ... 

Bromoethyl esters The cleavage of ethylene acetals using bromoform as bromine source is achieved by refluxing in benzene, also in the presence of AIBN and TsOH. 

Bromine source. Some ester enolates form a-bromoesters instead of the bro-moethylated products on reaction with 1,2-dibromoethane. 

Bromination. Bromination of aienes bromine source in the presence of H.O. and Oxidation of ethers. Ethers give ac... 

Bromination of allenes. Lithium bromide is the bromine source for addition to... 

Fundamentally, Br s role in Co - Br and Co - Mn - Br catalysis is that it catalyzes the oxidation of alkylaromatics by Co(III) and Mn(III). Since the discovery of Co-Br catalysis, it has been postulated that Br is formed from Br" added initially as a salt (CoBr2, NaBr) or HBr [35, 36, 38]. Organic bromides could also serve as bromine sources, but in order to be active, the organic bromide must be converted into inorganic bromide [8, 38]. Thus, there are two questions related to the nature of the bromine species in Co-Mn-Br catalysis what is the major catalytically active form of bromide and what is the active bromine radical species ... 

The Hu method exhibits similar substrate scope to that reported by Minisci primary and secondary benzylic, primary allylic, and primary and secondary aliphatic alcohols were shown to be viable substrates. The presence of HBr/Br2 can lead to undesirable bromination side reactions, depending on the alcohol substrate. However, the authors show that in some cases, with proper choice the bromine source, these side reactions can be avoided. For example, with... 

Transition metal-catalyzed regio- and sto-eoselective amino-bromination of olefins with TsNH2 and NBS as nitrogen and bromine sources. 4 Studies have appeared on the use of NBS in additions to alkenes and in the isomerization of alkenes. " ... 

A convenient procedure for the aminobromination of electron-deficient olefins 90 using Bromamine-T (TsNBrNa) as nitrogen and bromine source promoted by (diacetoxyiodo)benzene has been developed [96]. This heavy-metal-free protocol is highly efficient and affords the vicinal bromamines 91 with excellent regio-and stereoselectivities (Scheme 3.35). 

A series of unsaturated compounds 49, including a,p-unsaturated ketones, cinnamates, cinnamides and styrenes, have been aminobrominated to give products 50 with good yields and excellent diastereoselectivities under mechanical milling conditions, using TSNH2 and A-bromosuccinimide (NBS) as the nitrogen and bromine sources, promoted by (diacetoxyiodo)benzene (Scheme 6.19) [64],... 

Reproduced from Wu X-L, Xia J-J, Wang G-W. Amlnobromination of olefins with TsNH2 and NBS as the nitrogen and bromine sources mediated by hypervalent Iodine In a ball mill. Org Biomol Chem 2008 6 548-53, with permission from the Royal Society of Chemistry. 

Yadav first reported a one-pot oxidative u tz-Markovnikov bromohydroxy-lation and bromoalkoxylation of MBH adducts, accomplished at room temperature using LiBr as the bromine source and 2-iodoxybenzoic acid (IBX) as the oxidant. The process involves oxidation of MBH adducts with IBX to give p-ketomethylene compounds in situ, which undergo highly regioselective vicinal... 

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