Bromination product mixtures

I. Too great an excess of water in the reaction mixture appears to result in the formation of higher bromination products. 

With bromine trifluonde and 1% tin tetrachloride as a catalyst, 1,3-dichloro 2-fluoropropane gives 1,2,3 tnfluoropropane Without the catalyst, l-chloro-2,3 difluoropropane provides a four-component product mixture 1,2,3-trifluoro-propane, 3-chloro-l,l,2-tnfluoropropane, l-chloro-2,2,3-tnfluoropropane, and 1,1,2,3-tetrafluoropropane [9] (equations 7 and 8)... 

With Freon 112 or 113 as a solvent, fluonnation of pnmary butyl halides with bromine trifluonde can give mixtures of primary and secondary fluorides When 1,4 dibromobutane is the substrate, 93% l-bromo-4-fluorobutane and 1% 1-bro-mo-3-fluorobutane is obtained, with 1,4 dichlorobutane, the product contains 65% l-chloro-3-fluorobutane and 35% 1-chloro 4 fluorobutane When 4-bromo- or 4-chlorobutyl trifluoroacetate is used, the ratio of 4-fluorobutyl tnfluoroacetate to 3 fluorobutyl trifluoroacetate is 1 4 The effect of solvent is measured in another set of experiments When the reaction of bromine trifluonde and l,3-dichloro-2-fluoropropane in either Freon 113 or hydrogen fluoride is allowed to proceed to 40% conversion, the product mixture has the composition shown m Table 1 [/O] When 1 chloro 2,3-dibromopropane is combined with one-third of a mole of bromine trifluonde, both 1 bromo 3 chloro-2-fluoropropane and l-chloro-2,3-di-fluoropropane are formed [//] (equation 10)... 

Bromination of the homoconjugated 5-(difluoromethylene)-6 6-difluoro-2-norbornene yields different product mixtures under ionic and free-radical conditions 1771 (equation 6)... 

To a stirred solution of 5.7 g (0.02 m) of 4-benzyloxy-2-ureidoacetophenone in 100 ml of chloroform is added 3.2 g (0.02 m) of bromine. The mixture is stirred at room temperature for about 45 minutes and the solution is concentrated in vacuo at 25°-30°C. The amorphous residue (hydrobromide selt of 4-benzyloxy-a-bromo-3-ureidoacetophenone) is dissolved in 80 ml of acetonitrile and 98 g (0.06 m) of N-benzyl-N-t-butylamine is added. The mixture is stirred and refluxed for 1.5 hours, then it is cooled toOt in an ice bath. Crystalline N-benzyl-N-t-butylamine hydrobromide is filtered. The filtrate is acidified with ethereal hydrogen chloride. The semicrystalline product is filtered after diluting the mixture with a large excess of ether. Trituration of the product with 60 ml of cold ethanol gives 4-banzyloxy-Of-( N-benzyl-N-t-butylamino)-3-ureidoacetophenone hydrochloride, MP 200°-221°C (decomposition). 

A mixture of 24 g of 1,3-dimethyladamantane and BO ml of bromine was refluxed for 6 hours. The reaction product mixture was cooled, taken up in about 200 ml of chloroform, and poured onto ice. The excess bromine was removed by adding sodium hydrosulfite. The chloroform layer was separated from the aqueous layer, dried, concentrated in vacuo, and distilled at reduced pressure to yield 30.5 g of product having a boiling point of about 11B°C at 5-6 mm np = 1.5169-1.51B2. The product was identified by nuclear magnetic resonance (NMR) and elemental analyses as 1-bromo-3,5-dimethyladamantane. 

When the allylic cation reacts with Br to complete the electrophilic addition, reaction can occur either at Cl or at C3 because both carbons share the positive charge (Figure 14.4). Thus, a mixture of 1,2- and 1,4-addition products results. (Recall that a similar product mixture was seen for NBS bromination of alkenes in Section 10.4, a reaction that proceeds through an allylic radical.)... 

Next ask yourself, "What is an immediate precursor of p-bromotoluene " Perhaps toluene is an immediate precursor because the methyl group would direct bromination to the ortho and para positions. Alternatively, bromobenzene might be an immediate precursor because we could carry out a Friedel-Cralts methylation and obtain a mixture of ortho and para products. Both answers are satisfactory, although both would also lead unavoidably to a product mixture that would have to be separated. 

JHC961). When 2,7-naphthyridine (192) was brominated, a mixture of 4-bromo and 4,5-dibromo products was formed (70JHC419). In basic medium bromine converted benzo[6][l,8]naphthyridine-9-carboxaldehyde into the 3,7-dibromo-9-carboxylic acid (92JHC1197). 

Since thiophene derivatives, heterocyclic aromatic compounds, are sensitive toward electrophilic substitution reactions, the bromination of these compounds generally gives a mixture of mono-, di-, and other poly-substituted bromination products (ref. 19). However, we have recently found that BTMA Br3 is a useful... 

The bromination products, dibromide in methylene chloride and methoxybromide in methanol, are a mixture of erythro- and threo-diastereoisomers, obtained in a ratio, Erythro/Threo = 70 / 30, which does not depend on the substituents or on the solvent. As expected, the reaction in the protic solvent is fiilly regioselective, i.e. methanol only traps the intermediate... 

The phenol-contaminated sample was unique in yielding bromine containing none of the starting contaminant. Analysis of the bromine by FT-IR and INMR showed a complex mixture of brominated phenols and small amounts of other brominated hydrocarbons. The absence of phenol in the bromine product is not surprising, since phenol reacts with bromine at room temperature to make predominantly tribromophenol. 

These redistribution reactions are possible at atmospheric pressure under the action of MW irradiation is performed for a few minutes in the presence of the same catalysts [57]. These reactions with the less volatile germanium tetrabromide (44b) (b.p. 184 °C) have also been performed by use of the GS/MW process, without added catalyst (Tab. 7.4, entries 1 and 3) [15, 16]. In this instance, despite the use of weaker incident power, the temperature reached 420 °C, very much higher than that obtained under the action of MW irradiation of a reaction mixture containing AlBr3 (200 °C to 250 °C) (Tab. 7.4, entries 2 and 4). The presence of this catalyst considerably favors redistribution towards the dibrominated products (46b) (84% for R = nBu, 85% for R = Ph) relative to the monobrominated compounds (46a), which are the major products of the GS/MW process (78% and 43% respectively). The tri-brominated products (46c), the most difficult to prepare, have been obtained with a rather high selectivity (73 to 80%) by use of the catalytic process under the action of MW [57]. In this reaction, therefore, the GS/MW process seems less effective than the MW-assisted and AlX3-catalyzed process. 

Method B. Bromination TMA-Br3 (1.54 g, 10 mmol) and (PhC0)202 (0.24 g, 1 mmol) is added to the alkylarene (10 mmol) in PhH (20 ml) at room temperature and the mixture is stirred until the colour disappears and the evolution of HBr stops. H20 (20 ml) is added and the organic phase is separated, washed well with H20 and aqueous Na2CO, (sat. soln.), dried (Na2S04), and evaporated to yield the brominated product. 

Photolytic. When a dilute aqueous solution (1-10 mg/L) of bromacil was exposed to sunlight for 4 months, the TV-dealkylated photoproduct, 5-bromo-6-methyluracil, formed in small quantities. This compound is less stable than bromacil and upon further irradiation, the de-brominated product, 6-methyluracil was formed (Moilanen and Crosby, 1974). Acher and Dunkelblum (1979) studied the dye-sensitized photolysis of aerated aqueous solutions of bromacil using sunlight as the irradiation source. After 1 h, a mixture of diastereoisomers of 3-5ec-butyl-5-acetyl-5-hydroxyhydantoin formed in an 83% yield. In a subsequent study, another minor intermediate was identified as a 5,5 -photoproduct of 3-5ec-butyl-6-methyluracil. In this study, the rate of photooxidation increased with pH. The most effective sensitizers were riboflavin (10 ppm) and methylene blue (2-5 ppm) (Acher and Saltzman, 1980). Direct photodegradation of bromacil is not significant (Acher and Dunkelblum, 1979 Ishihara, 1963). 

The bromide has an equal probability of attacking either carbon atom two or carbon atom four, so why is the product mixture not 50 percent of each At low temperatures, the bromine doesn t move very ftir after giving up its H, so it s near Ccirbon two (1,2-addition). At high temperatures, the bromine donates an H and can move, so it s able to form the more stable product (a disubstituted C=C). 

Hydrogen bromide gas may be produced by combustion of hydrogen in bromine vapor at 37.5°C using a catalyst such as platinized asbestos or platinized silica gel. Unreacted free bromine is removed from the product by passing the gaseous product mixture over hot activated charcoal. Hydrogen bromide formed may be absorbed in water to obtain the acid or may be cooled and liquefied for shipment in cylinders. 

Sodium bromide can be made by passing bromine through an aqueous solution of sodium hydroxide or carbonate in the presence of a reducing agent, such as ammonia, hydrazine, activated charcoal, or Fe2+ ion. A typical method involves adding iron to bromine water to form ferrosoferric bromide, FelFeBrs]. This double salt is dissolved in excess water followed by addition of sodium carbonate. The product mixture is filtered and the filtrate is evaporated to crystallize sodium bromide. The overall reaction may be written as follows ... 

The reaction of 1,5-naphthyridine (1) with bromine in chloroform does not yield any brominated products (54JCS1879). However, treatment of (1) with bromine in oleum was found to give a mixture of the 3-bromo- (13) and the 3,7-dibromo-l,5-naphthyridines (14) in 10% and 35% yield respectively (65JOC1607, 67LA(707)242). With bromine in pyridine the yields were 27% of (13) and 10% of (14) (68JOC1384), and application of this procedure to 1,6-naphthyridine (2) gave a mixture of 3-bromo- (15), 8-bromo- (16) and 3,8-dibromo-... 

In view of this apparent resistance of triazolium to bromination with electrophilic bromine, it is interesting to discover that 1,3-dimethyl-1,2,3-triazolium tosylate (71) was 4-brominated by bromine and NBS. When the 4-bromo salt (72) is dissolved in base, an equilibrium is established containing unbrominated salt (71) and 4,5-dibromo salt (73). Presumably, base converts 72 into an ylid, which is further brominated by 72. A similar product mixture was obtained from the isomeric 5-bromo tosylate (74) [69ACS(B)2733 71ACS(B)249] (Scheme 27). 

A mixture of products, that contains regioisomeric bromohydrin acetates, is obtained20 by the bromine/acetic acid oxidation of an alkene having a tertiary perfluoroalkyl group in the allylic position. It is interesting that a different composition of the product mixture 61-63 is obtained depending on the addition of bromine or of the alkene to the reaction mixture.20... 

A -(2-Fluoro-2,2-dinitroethyl)hydroxylamine (1) is oxidized by 3-chloroperoxybenzoic acid or bromine to afford oxime 2.218 This compound is unstable and over the course of several weeks at ambient temperature it rearranges quantitatively to amide 3.218 Further oxidation of the oxime 2 with nitric acid or aqueous chromic acid gives a product mixture, from which bis(fluorodinitromethyl)furoxane 4 is isolated.218... 

In the absence of AlBr3, the kinetic product is the 1-bromide, 74. Further bromination, if it occurs, takes place at the most remote bridgehead positions available to give 75 and 76. When AlBr3 is present in the reaction mixture, characteristically decreased selectivity is observed (see also Section II.B). Bromination at the 4-position is able to compete effectively and 77 is obtained as one of the bromination products. 

The most successful naphthoxidine-derived dye was 19 [26846-51-5], which is prepared by bromination of naphthoxidine in acetic acid in the presence of a catalytic amount of iodine or iron. The commercial dye is in fact a mixture of various brominated products, of which 19 is the predominant component. The product is a clear blue disperse dye suitable for acetate and polyester fibers. 

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