Ammonium tribromide

Quaternary ammonium tribromides in methanol-dichloromethane did not brominate the furan ring of 3-methyl-8//-cyclohepta[/>]furan-8-one. Instead, the 7-bromo derivative was formed (92BCJ295). 

BROMINATION AND OXIDATION WITH BENZYLTRIMETHYL-AMMONIUM TRIBROMIDE... 

As these solid agents, some quaternary ammonium tribromides such as pyridinium hydrobromide perbromide (ref. 1), phenyltrimethylammonium tribromide (ref. 2), tetramethylammonium tribromide (ref. 3), and tetrabutyl-ammonium tribromide (ref. 4) have already been reported as mild and selective brominating agents (Fig. 1). 

Similarly, we found that quaternary ammonium tribromides such as TBA Br3 and BTMA Br3 are useful agents for the a-bromination of acetyl derivatives (Fig. 16) (ref. 25). 

There are a number of methods for the oxidation of primary alcohols or ethers to dimeric esters, and secondary alcohols to ketones. We recently also found that quaternary ammonium tribromides, especially BTMA Br3, are useful oxidizing agents for the purpose described above (ref. 31). 

Sebacid acid dinitrile, 50, 20 SELECTIVE o-BROMINATION OF AN ARALKYL KETONE WITH PHENYL-TRIMETHYL AMMONIUM TRIBROMIDE 2-BRQM0ACETYL-6-METH-OXYNAPHTHALENE AND 2,2-DI-BROMOACETYL-6-METHOXYNAPH-THALENE, 53, 111 Shikimic acid, 50, 27 Silver benzoate, as catalyst in decomposition of diazoketones, 50, 78... 

Free halogens are generally inconvenient to use, owing to their toxic and corrosive nature, but can be replaced by quaternary ammonium polyhalides. Quaternary ammonium tribromides are well established [e.g. 1] as solid, readily handled and relatively non-toxic alternatives for electrophilic bromine. More recently, other quaternary ammonium polyhalides have been produced, which together with the tribromides, have wide application as catalysts or in stoichiometric quantities in electrophilic substitution and addition reactions, oxidations, etc. 

Quaternary ammonium tribromides can also be produced in situ from the quaternary ammonium bromide, sodium hypochlorite and sodium bromide and can be used, for example, in electrophilic addition reactions reaction with alkenes and alkynes. 

Alkenes are converted in high yield by the preformed ammonium tribromides into the corresponding dibromoalkanes [2,3]. 

As an alternative to the use of quaternary ammonium tribromide, A -bromosuccin-imide tetra-n-butylammonium bromide converts alkenes into the dibromoalkanes generally in high yield (>90%) [8]. It is probable that the ammonium tribromide is formed in situ. 

Polymer-supported ammonium tribromides convert methyl and methylene ketones into the corresponding a-bromo ketones in yields varying from 55 to 75% (see Section 2.3) [9]. 

The stoichiometric reaction of sulphides with ammonium tribromides under basic conditions leads to sulphoxides [10]. In a modified procedure, oxidation in I80-enriched water produces the 180-labelled sulphoxide [11]. 

In concentrated aqueous solution ammonium bromide is converted by electrolysis or the action of bromine into ammonium tribromide, NH4Br,Br2,.16 This substance is unstable, and forms large columnar crystals with a colour similar to that of potassium dichromate. Ammonium bromide combines with ammonia to form complex de-... 

Cyclic ketals of some steroid ketones have been brominated directly in the "a -position without destruction of the ketal [154,133]. The best reagent appears to be phenyltrimethyl-ammonium tribromide (PhMesN- - Brs ) in anhydrous tetrahydrofuran [ 133]. Dissociation of the tribromide ion probably... 

Scheme 18.32 and a wide range of cocatalysts including the commonly tested tetrabutylammonium halides (F-, Cl-, Br- and I-) and iV,iV -dimethyl-aminopyridine as well as the remarkable phenyltrimethylammonium tribromide (PTAT [PhMe3N] [Br3] ). The combination Al(TPP)Cl and phe-nyl-trimethyl ammonium tribromide produced cyclic carbonates in excellent yields, this combination displaying the best compromise between the Lewis acidity of the centre, the leaving ability of the axial halide and the nucleo-philicity of the anion in the cocatalyst. PTAT showed a better activity than the tetrabutylammonium halides, whereas the neutral DMAP delivered the worst conversion of this series. ... 

Correlation analysis of reactivity in the oxidation of benzyl alcohol by benzyltrimethyl-ammonium tribromide has revealed that the reaction involves an almost synchronous cleavage of the a-C—H and O-H bonds. An intermediate complex between the aldehyde hydrate and tribromide ion is decomposed in the rate-limiting step of the oxidation of aliphatic aldehydes to the corresponding carboxylic acids by benzyltrimethylammon-ium tribromide. ... 

Preparation by diazotization of 3-amino-4-hydroxyacetophenone and replacement of the diazonium group by bromine (Sandmeyer reaction) (51%) [1953]. Preparation by Fries rearrangement of 2-bromophenyl acetate with aluminium chloride without solvent at 100-120° [1817,1946,1947,1954], (68%) [1817]. Also obtained by reaction of ammonium tribromide on 4-hydroxyacetophenone in methylene chloride-methanol mixture [1955]. 

Preparation by reaction of ammonium tribromide on 4-hydroxyacetophenone in methylene chloride-methanol mixture [4403]. 

Jing, H. Chang, T Jin, L. Wu, M. Qiu, W. Ruthenium Salen/Phenyl Trimethyl Ammonium Tribromide Catalyzed Coupling Reaction of Carbon Dioxide and Epoxides. Catal. Comm. 2007, 8, 1630-1634. 

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