Phenols with bromine

Several methods for direct o/t/to-bromination and < /t/to-dibromination of phenols have been reported (refs. 4,5). Pearson et al. (ref. 6) found that treatment of phenols with bromine in the presence of a large excess of f-butylamine at - 70°C gave 2-bromo- or 2,6-dibromophenols in good yields. Recently, Schmitz et al. (ref. 7) showed that the reaction between phenol and AT,A -dibromomethylamine efficiently affords 2,6-dibromophenol. 

In Table 1 was shown the results of bromination of phenol with bromine, NBS, and AT-bromodibutylamine (NBB) (ref. 8) in dichloromethane. 

Table 1. Bromination of Phenol with Bromine, NBS, and iV-Bromodibutylamine (NBB) )...

In general, it is difficult to carry out a step-by-step bromination of phenols with bromine, since phenols react very rapidly with bromine, which leads to the polybromo-substituted phenols. We found that the reaction of phenols with calculated amounts of tetrabutylammonium tribromide (TBA Br3) or BTMA Br3 in... 

A number of the reactions of phenols are typical of ends. Thus they are readily halogenated in the ortho and para positions, with a marked tendency for polyhalogenation. Bromination of phenol with bromine in carbon tetrachloride gives 4-bromophenol, but 2,4,6-tribromophenol is formed with bromine water. 

Identification of Phenols.—The reactions of phenols which are of particular value in their identification, are those that take place with alkalies, ferric chloride, and bromine water. Most phenols react with an aqueous solution of sodium hydroxide to form soluble salts, but are insoluble in a solution of sodium carbonate. The behavior of phenols with these two reagents shows their weakly acidic properties, and serves to distinguish them from acids. Phenols which contain strongly negative substituents decompose carbonates, and show all the properties of acids. It is difficult, therefore, to identify as a phenol substances which contain such substituents. Ferric chloride produces marked colorations in aqueous solutions of most phenols. The reagent produces a similar effect with certain other compounds, and the formation of a color with ferric chloride can be taken, therefore, only as an indication of the presence of a phenol. With bromine water most phenols yield a precipitate of a brominated phenol. Other compounds, amines for example, are also converted into insoluble substitution-products by bromine water. Notwithstanding this fact the test is of value. Many phenols form colored products when heated with phthalic anhydride and concentrated sulphuric acid. The reaction will be described under phenolphthalein (558, 639). 

From the phenol with bromine in carbon disulfide See Vogel, p 679... 

Apart from acid-base titrations various addition-, substitution- and redox-reactions have been found to be of analytical interest. Iodine numbers of fats and essential oils may be determined i and bromine may be used to titrate organic compounds which can form bromoderivatives i. For the titration of phenol with bromine the addition of sodium acetate has been recommended. Redox reagents are in acetic acid chromium(VI) oxide, sodium permanganate, bromine, titanium(III) chloride and chromium(II) saltsi32,i33 xhe titrations are usually carried out in perchloric acid solutions and in an inert atmosphere but traces of water are tolerable. 

It should be noted that phenol also reacts very readily with bromine to give the corresponding 2.4,6-tribromophenol, C6H2(OH)Br,v... 

Certain phenols give white bromo derivatives with bromine water. 

Treatment of phenol with excess aqueous bromine is actually more complicated than expected A white precipitate forms rapidly which on closer examination is not 2 4 6 tribro mophenol but is instead 2 4 4 6 tetrabromocyclohexadienone Explain the formation of this product... 

Bromination can be conveniently effected by transfer of bromine from one nucleus to another. As the Friedel-Crafts isomerization of bromoaromatic compounds generally takes place through an intermolecular mechanism, the migrating bromine atom serves as a source of positive bromine, thus effecting ring brominations (161,162). 2,4,6-Tribromophenol, for example, has been prepared by bromination of phenol with dibromobenzene. 

In the petroleum (qv) industry hydrogen bromide can serve as an alkylation catalyst. It is claimed as a catalyst in the controlled oxidation of aHphatic and ahcycHc hydrocarbons to ketones, acids, and peroxides (7,8). AppHcations of HBr with NH Br (9) or with H2S and HCl (10) as promoters for the dehydrogenation of butene to butadiene have been described, and either HBr or HCl can be used in the vapor-phase ortho methylation of phenol with methanol over alumina (11). Various patents dealing with catalytic activity of HCl also cover the use of HBr. An important reaction of HBr in organic syntheses is the replacement of aHphatic chlorine by bromine in the presence of an aluminum catalyst (12). Small quantities of hydrobromic acid are employed in analytical chemistry. 

Discussion. A number of phenols can be substituted rapidly and quantitatively with bromine produced from bromate and bromide23 in acid solution (Section 10.131). The determination involves treating phenol (Note 1) with an... 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Calo et al. (ref. 5) studied solvent effects on selective bromination of phenol with NBS and found the selectivity of bromination depended on the polarity of the solvents. But thereafter no investigation concerning the solvent effects was reported. We report the effects systematically. 

The results of the bromination of phenol with NBS compared with bromine in various solvents are shown (Fig. 1). NBS was not added as the solution in solvent but solid powder. 

Fig. 1. Plots of dielectric constant vs selectivity of bromination of phenol with Br2 (left) and NBS (solid powder) (right). ort/io-Bromophenol (A), para-Bromophenol ( ).

Table 4. Bromination of 2-Substituted Phenols with NBS, Bf2, and BTMA.Br3 ) OH...

Fig. 2 Selectivity of orf/io-bromide (left) and dibromide (right) depending on reaction temperature in the bromination of 2-substituted phenols with NBS (solid powder) and (/-Pr)2NH. 2-allylphenol ( ), o-cresol (A), 2-bromophenol (A), and 2-chlorophenol (O).

The mechanism of the orf/to-dibromination of phenol with NBS in the presence of amines is considered as follows. The hydrogen bonding between phenol and N-bromoamine which are generated from the reaction of NBS and amines (ref. 14), is the driving force, and causes the bromination at one o/t/io-position of phenol and regeneration of the amines. A catalytic amount of the amines is enough because of the regeneration of the amines. The repetition of the above process causes one more substitution at the other orf/io-position of 2-bromophenol. In the cases of 2-substituted phenols the orf/io-bromination can occur only once (Scheme 5). 

Fig. 7. Bromination of phenols with styrene polymer-bound BTMA Br3...

Fig. 9. Selective para-bromination of phenols with Amberlyst-A26 tribromide...

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. 

The actual attacking species is less clear than with bromine or chlorine. Iodine itself is too unreactive, except for active species such as phenols, where there is good evidence that I2 is the attacking entity.There is evidence that AcOI may be the attacking entity when peroxyacetic acid is the... 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

According to K. H. Meyer, this surprising reactivity—which is also encountered amongst the enols—is explained by the fact that the OH-group activates the double bond adjacent to it and the two neighbouring double bonds of the conjugated system (Thiele s theory) are also involved in this activation. Phenol, therefore, can yield 1 2- and 1 4-substitution products with bromine, addition reactions first taking place ... 

Theory Phenol interacts with bromine whereby the former undergoes bromination to yield a water-insoluble 2, 4, 6-tribromophenol. This reaction takes place quantitatively as shown below ... 

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