Pyridinium bromide dibromide

D-4 1814 TMB-4 1,1 -trimethylene- 56-97-3 bis(4-formyl-pyridinium) bromide (bromide) (or chloride) dioxime 3613-81-9 trimedoxime 1,3-bis (chloride) (4-formylpyridinium)propane dibromide (or dichloride) blsoxime 32... 

Bromination of an olefin and double dehydrobromination of the resulting 1,2-dibromide is a classical method for the generation of 1,3-dienes (Table 1). Bromination of a double bond can be done with molecular bromine or, more conveniently, with pyridinium bromide perbromide . A variety of bases has been employed for dehydrobromination. While potassium hydroxide and sodium methoxide have been used for a long time, lithium carbonate-lithium chloride in DMF or hexamethylphosphoric triamide (HMPA) works well in many cases . Double dehydrobromination with hindered bases such as potassium r-butoxide or diazabicyclononene (DBN) and diazabicycloundecene (DBU) give good results. 

Improvements in the preparation and dehydrohalogenation of w o-stilbene dibromide [Org. Syntheses, Coll. Vol. 3, 350 (1955)] are as follows. ra 5-Stilbene (20 g.) is heated with 400 ml. of acetic acid on the steam bath until dissolved, 40 g. of pyridinium bromide perbromide is added, and the mixture is heated on the steam bath and swirled for 5 minutes, meso-Stilbene dibromide separates at once in pearly white plates. The mixture is cooled to room temperature, and the product is collected and washed with methanol. The yield of dibromide, m.p. 

Dicationic IHbased surfactant l,10-(butane-l,4-diyl)-bis(3-(tetradecyloxycarbonyl)pyridinium) dibromide. Monocationic l-ethyl-3-(tetradecyloxycarbonyl)pyridinium bromide. 

Halogenation of indoles has been performed with a great variety of halogenating agents, which include, in addition to halogens, dioxan dibromide, pyridinium bromide perbromide, N-bromosuccinimide, N-iodosuccinimide, ICl, chloramine T-KI, hypochlorite and /-butyl hypochlorite 394). 

For example, 3-bromopyridine is formed when pyridine is reacted with bromine in the presence of oleum (sulfur trioxide in cone, sulfuric acid) at 130 °C (Scheme 2.4). Direct electrophilic substitution is not involved, however, aszwitterionic (dipolar) pyridinium-A-sulfonate is the substrate for an addition of bromide ion. Subsequently, the dihydropyridine that is formed reacts, possibly as a dienamine, with bromine to generate a dibromide, which then eliminates bromide ion from C-2. It is notable that no bromination occurs under similar conditions when oleum is replaced by cone, sulfuric acid alone instead, pyridinium hydrogensul-fate is produced. 

In a 125-mL Erlenmeyer flask dissolve 2 g of -stilbene in 40 mL of acetic acid, by heating on the steam bath, and then add 4 g of pyridinium hydro-bromide perbromide. Mix by swirling if necessary, rinse crystals of reagent down the walls of the flask with a little acetic acid and continue the heating for 1 -2 min longer. The dibromide separates almost at once in small plates. Cool the mixture under the tap, collect the product, and wash it with methanol yieldofcolorlesscrystals, mp236-237°C,about 3.2 g. UseO.5 g of this material for the preparation of diphenylacetylene and turn in the remainder. 

V. Braun reaction Cyanogen bromide. Phosphorus tribromide. Piperidine. Thionyl chloride. Bromination Aluminum bromide. Aluminum chloride. Boron tribromide. Bromine chloride. N-Bromocaprolactam. N-Bromosuccinimide. Bromotrichloromethane. Cupric bromide. Dibenzoyl peroxide. l,3-Dibromo-5,5-diraethylhydantoin. 1,2-Dibromotetrachloromethane. HBr-scavengers acetamide and potassium chlorate. Iodine. Iodine monobromide. Iron. Mercuric acetate. Phenyl trimethylammonium perbromide. Phosphorus trichloride. Pyridine. Pyridine perbromide. Pyridinium hydrobromide perbromide. Silver sulfate. Sodium acetate. Sodium hypobromite. Sulfur. Sulfur monochloride. Tetramethylaramonium tribromide. M-Tribromoacetophenone. Trichloromethane sulfonyl bromide. Trilluoroacetyl hypobromite. Triphenylphosphine dibromide. 

Treatment of pyridinium benzoate with carbonyl dibromide in toluene gives benzoyl bromide [1919] ... 

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