Brominations Conducted With Pyridinium Bromide Perbromide

Abstract

Previously reported work has indicated that pyridinium bromide perbromide (pyridine hydrobromide perbromide) can be considered a general brominating agent which may be used in brominations ordinarily performed with molecular bromine, such as substitution on aromatic rings and additions to double bonds (1). It is not a specific brominating reagent such as N-bromosuccinimide (2) which is recommended for brominating the allyl position of an olefin. However, the use of peroxide type catalysts (3,4) and aluminum or zinc chloride (5) have extended the scope of the brominations possible with N-bromosuccinimide. An excellent review of the reactions performed with brominating agents other than pyridinium bromide perbromide has been recently written by Carl Djerassi (6).Pyridinium bromide perbromide (7, 8) CsHeNBr • Brz is a red crystalline stable salt having the melting point 135-136°( dec.) with previous softening. The reagent has many advantages over dangerous liquid bromine. It is easily handled and stored and may be conveniently weighed. From its structural formula one would suspect that this perbromide can release free bromine, thus when substituted for bromine in any standard bromination the reaction should be expected to proceed in a normal manner. The experiments reported in this paper seem to verify the efficacy of pyridinium bromide perbromide as a substitute for bromine. The quantities of this reagent used were based on the presence of 45% available bromine, although the supplier has indicated 45-50% bromine available. EXPERIMENTAL Materials: The pyridinium bromide perbromide (PBPB) used in this study was supplied by Jasons Drug Company of Brooklyn, New York.6-Bromo-2-naphthol (9). /S-Naphthol (36 g., 0.25 mole) and 100 ml. of glacial acetic acid were placed in a 500-ml. round-bottom three-neck flask with a condenser, stirrer, and dropping-funnel. Pyridinium bromide perbromide (178 g.) was dissolved in 100 ml. of hot glacial acetic acid, and this solution -was added to the /3-naphthol through the droppingfunnel over a period of twenty minutes. The reaction was cooled slightly so as to effect a gentle reflux. The 0-naphthoI dissolved entirely as the addition took place. Then 25 ml. of water was added to the flask and the entire mixture heated to boiling. After Organic Syntheses (9), 39 g. of mossy tin was added and the mixture was refluxed for two hours. At the end of this period the mixture was cooled to 50°and filtered with suction.To the filtrate was added 1.5 liters of water. A copious white precipitate formed which was washed three times with divided portions of 250 ml. of water. Upon air-drying the solid, 25 g. of a slightly pinkish powder, m.p. 122-124°, was obtained; yield 45.5%. For the classical

From Conventional Lewis Acids to Heterogeneous Montmorillonite K10: Eco‐Friendly Plant‐Based Catalysts Used as Green Lewis Acids

“…Bromination reactions are defined as electrophilic aromatic substitution (EA r S) in which a bromine cation is also produced from a Lewis acid, such as FeBr 3 , pyridinium bromide, and pyridinium bromide perbromide . This aromatic bromination is often incomplete and leads, in most cases, to a mixture of mono‐ and polybromoaromatic products .…”

An alternative method for the regio- and stereoselective bromination of alkenes, alkynes, toluene derivatives and ketones using a bromide/bromate couple

“…2 The use of liquid bromine for bromination is still very common in industry as well as in academia, in spite of its hazardous effects, probably due to lack of a suitable alternative. Although, besides liquid bromine, several other safer and user-friendly brominating agents, such as pyridiniumbromide-perbromide, 3 quaternary ammonium tribromide, 4 Amberlyst-A-26 tribromide, 5 pentylpyridinium tribromide, 6 1,2-dipyridiniumbis(tribromide)-ethane (DPTBE), 7 and N-bromosuccinimide (NBS) 8 have been developed, preparation of all these reagents involves liquid bromine at some stage. As a part of our broad program to explore the desired bromination reaction with minimum byproducts or waste generation, as well as elimination of the use of hazardous liquid bromine, we have developed a solid green reagent utilizing the liquid bromine precursor of bromine manufacture.…”

Review for metal and organocatalysis of heterocyclic C-H functionalization

“…The reaction of pyrrole derivatives 56 and nitro derivatives 57 in the presence of various chiral bifunctional organocatalysts 58 in dichloromethane to synthesized chiral pyrrole derivatives 59 [180][181][182]. (Scheme 18) Direct β-indolylation of enals, the investigation of an efficient metal-free organocatalysed C-H α-arylation reaction of enals remains highly challenging [183][184][185][186][187]. There is very few reports about the metal free approach for the direct C(sp2)-C(sp2) cross-coupling α-indolylation of enals from unfunctionalized indoles and enals.…”