Halides bromide

Reaction with Other Halides. Bromide ion is oxidi2ed by chlorine to bromine. This is the basic reaction in the production of bromine from seawater, brines, or bitterns. 

An important series of reactions, which illustrates the diversity of behaviour to be expected, is the comproportionation of halates and halides. Bromides are oxidized quantitatively to bromine and iodides to iodine, this latter reaction being much used in volumetric analysis ... 

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

Treatment of the acylated glycosyl halide (bromide or chloride) of the opposite anomeric configuration with silver fluoride in acetonitrile was the method initially developed40 for the synthesis of the less stable anomers, as exemplified by the synthesis of peracylated /S-D-glucopyranosyl fluoride40 from the corresponding a-bromide. It has... 

Also in the case of intennediate 374, a lithium-copper transmetallation with a copper(I) halide (bromide or chloride) allowed one to carry out the conjugate addition [to electrophilic olefins R CH = CH2Z (Z = COR, CO2R) giving compounds 381 in 31-76% yield], the acylation (with acyl chlorides yielding ketones 382 in 35-65% yield) and dimerization [using copper(II) chloride as the additive, to give compound 383 in 59% yield] processes ... 

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93 4] or other similar halide compounds were added to the gasoline along with TEL to form volatile lead halide compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead halides (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead halide renders the catalytic site inactive. 

Potassium bromide, usually referred to as bromide, is the primary restrainer found in most developers. Bromide has the effect of holding back the overall action of the developer, reducing the effective sensitivity of the film, and diminishing the amount of useful density created in the shadow areas. By inhibiting the reduction of silver halide, bromide also acts to increase contrast. This action varies with different developers. 

Aryl halides (bromides and iodides) reacting via ate complexes... 

Interestingly, many electron-deficient heterocyclic and aryl bromides or iodides are sufficiently activated to react with commercially available zinc powder.22,2211 In the case of benzylic halides, bromides and even chlorides can be used.44 The benzylic chloride requires a longer reaction time compared to its corresponding bromide derivative (Equations (12) and (13)). 

Acid chlorides are suitable electrophiles. As aromatic and 1-alkenyl halides, bromides and iodides are generally good substrates. Until quite recently, the use of the corresponding chlorides, which are cheaper and often more readily accessible, had been limited to that bearing a strongly electron-withdrawing substituent at a proper position. The use of nickel catalyst [47], bulky phosphine [119], and heterocyclic carbene ligand (Scheme 23, Table 1) [116] enabled aryl chlorides to take part in the reaction. 

Lithium halides (bromide or Iodide) may well modify the Lewis character of the zinc atom, probably via a zincate species [53], and prevent the efficient coordination of the zinc atom to the double bond, coordination which is required for the carbocyclization. Thus, in the Rieke method, it is essential to wash the active zinc thoroughly since the lithium naphthalenide reduction of zinc bromide also generates lithium bromide, which is detrimental to the success of the reaction. Indeed, the insertion of Rieke s zinc in the presence of LiBr leads to the linear organozinc iodide but not to the cyclic product [52]. 

Treatment of lithium acetylide with a primary alkyl halide (bromide or iodide) or with aldehydes or ketones produces the corresponding monosubstituted acetylenes or propargylic alcohols. Mercuric ion-catalyzed hydration of these furnishes methyl ketones and methyl a-hydroxy ketones, respectively. 

Nature of the halide. Bromides generally are best iodides have a tendency to undergo the Wurtz reaction. With chlorides, use Li containing 1-2% Na. 

The best results are obtained with the use of alkali metal hydrides (NaH, KH) in THF, DME, or DMF. The reaction works well in THF or DME with activated halides such as ethyl bromoac-etate, ten-butyl bromoacetate, - ethyl 2-bromobutyratc, ethyl T-broniobulyrale.- (iodom-ethyl)trimethylstannane, " (iodomethyl)trimethylsilane, benzoyl bromide,- benzyl bro-mide, - farnesyl bromide,- " alkyl 4-bromocrotonates, l-(bromomethyl)naphtalene,- andN-bromomethylphthalimide but gives poor results with primary alkyl halides.- Primary and secondary alkyl halides, bromides and iodides (Scheme 8.16), react satisfactorily in dMF or DMSO, although bulky electrophiles give poor results. In DMSO the expected product is frequently contaminated by the dialkylation product. ... 

In an extension of this method, Koenigs and Knorr subsequently reported that reaction between acylated glycosyl halides (bromides, chlorides, or iodides) with alcohols, in the presence of silver promoters (oxide or carbonate) furnished 1,2-trans alkyl glycosides. 

Sulfonyl chlorides are totally defunctionalized (with loss of SO2 also) during coupling with Grignard reagents. Alkenylmagnesium bromides and alkyl halides (bromides and iodides) are coupled in the presence of FeCls and TMEDA, whereas for the formation of ArMgBr and RX a complex derived from FeCls and 1 has been identified. ... 

Allylation. Amalgamated Sm promotes reaction of allyl halides (bromide, iodide) with carbonyl compounds. Diallylation of esters occurs. ... 

Sulfides. Symmetrical sulfides can be prepared in high yield from the reaction of alkyl halides and sodium sulfide in water with this phase-transfer catalyst. Unsymmetrical sulfides are prepared from alkyl halides and sodium mercap-tides. Secondary alkyl halides react more slowly than primary halides bromides are more reactive than chlorides. ... 

The authors performed careful measurements of the heats of solutions of well characterised Zr and Hf halides (bromides and chlorides) in aqueous solutions of an initial pH of 3, 6 or 9 (pH adjusted by high purity NaOH or HCIO4) or in deionized water. Due to the dissolution of Zr and Hf halides, the final solution pH fell to a much narrower range between pH 2.5 and 3.5. Total Zr concentrations were varied between 10 and 10 m. The results were interpreted by the reaction... 

Cul was later found to catalyse the phosphonation of aryl halides (bromides or iodides) by dialkyl hydrogenphosphonates in hmpa ... 

Like heat and light stabilizers, flame retardants containing bromine or chlorine act as free-radical scavengers. They interrupt combustion essentially by replacing free hydrogen and hydroxyl radicals with halide (bromide or chloride) radicals that prevent the combustion reaction from continuing, according to a cyclic process (simplified here) ... 

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