Tribromophenol-bromine

Tribromophenol is easily prepared by adding bromine water to an aqueous solution of phenol until the former is no longer decolorized. An excess of bromine gives tribromophenol-bromine (for its preparation see Kohn and Sussmann458), which readily gives up one Br+ and thus functions as a brominat-ing agent. It liberates iodine from iodide,459 so that tribromophenol is formed, with consumption of 6 atoms of Br per mole of phenol, when phenol is titrated with bromine (bromide-bromate), KI, and thiosulfate. 

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

Brominated Phenols. Tribromophenol [75-80-9] and dibromophenol [615-58-7] are both prepared through bromination of phenol. These are not actually used as reactive flame retardants, but rather as starting materials for other flame retardants such as BTBPE [37853-59-1] and epoxy oligomers. 

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. 

During certain substitution reactions, the carboxyl group is often replaced by the entering group. An example is fuming nitric acid, which results in the formation of trinitrophenol. Another is the bromination of saUcyhc acid in aqueous solution to yield 2,4,6-tribromophenol [25376-38-9] (eq. 6). 

Oxidation of saligenin with chromic acid or silver oxide yields saUcyladehyde as the first product. Further oxidation results in the formation of sahcyhc acid, which is also obtained when saligenin is heated with sodium hydroxide at 200—240°C. Chlorination of an aqueous solution of the alcohol gives 2,4,6-trichlorophenol, and bromination in an alkaline medium yields 2,4,6-tribromophenol and tribromosaligenin. When saligenin is heated with one mole of resorcinol in the presence of anhydrous zinc chloride, 3-hydroxyxanthene forms. 

Phenols and phenol ethers readily undergo mono-, di-, or trihromination in inert solvents depending on the amount of bromine used. In water the main product is the 2,4,6-tribromophenol [118-79-6] C H Br O (23). In water or acetic acid anilines also give the tribrorninated product (25). 

Tribromophenol can be further brominated in buffered acetic acid to give 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one [20244-61-5] a useful hrominating agent (26). 

Treatment of p-hydroxybenzoic acid with aqueous bromine leads to the evolution of carbon dioxide and the formation of 2,4,6-tribromophenol. Explain. 

Add to another portion a drop of bromine water. A white crystalline precipitate of tribromophenol is formed. 

In the presence of excess bromine, the first-order rate coefficient was 10.3 x 10" 5, but kinetic studies here were complicated due to rapid reaction of bromine with the 2,4,6-tribromophenol to give the intermediate (LXII), with SO3 replaced by Br) which slowly decomposed with a rate coefficient k2 to give two products. By analysis in terms of two consecutive first-order reactions, the values of k2 and k2 were determined as 9.2 x 10"5 and 3.75 x 10"4 and the latter rate being the faster means that two moles of bromine were consumed for every mole of sulphonate undergoing substitution in fact, more than two moles were consumed, the reason for this being undetermined. 

A. 2,i,l,()-Tetrabromo-2,5-cyclohexadien-l-one. A mixture of 66.2 g. (0.2 mole) of 2,4,6-tribromophenol (Note 1), 27.2 g. (0.2 mole) of sodium acetate trihydrate, and 400 ml. of glacial acetic acid is placed in a 1-1. Erlenmeyer flask and warmed until a clear solution is obtained. The temperature of the solution is approximately 70°. The solution is magnetically stirred and cooled to room temperature to produce a finely divided suspension of the phenol. A solution of 32 g. (0.2 mole) of bromine in 200 ml. of glacial acetic acid is added dropwise over 1 hour (Note 2). The resulting mixture is kept at room temperature for 30 minutes and is then poured onto 2 kg. of crushed ice. The yellow solid which separates is removed by suction filtration after the ice has melted, and the damp crystals are dissolved in the minimum quantity of warm chloroform (Note 3). The upper aqueous layer is removed by means of a pipet fitted with a suction bulb. The dienone crystallizes from the... 

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. 

For the organic contaminants, the required bromine product quality wilt also be site specific. If the catalytic oxidation unit is dedicated to a single bromination process, phase separation and drying may be the only purification required. Contaminants in the recovered bromine which are either the starting materials or products of the original bromination reaction should not present a problem if present in bromine recycled to the bromination reactor. In this case, the catalytic reactor would be operated to minimize the formation of undesirable brominated byproducts. For example, if phenol is present in the waste HBr from a tribromo-phenol manufacturing process, minor tribromophenol contamination of the bromine recycled to the reactor should not be a problem. Similarly, fluorobenzene in bromine recycled to a fluorobenzene bromination process should not present a problem. 

Tribromophenol and other simple brominated phenols (No. 66, 2005) Tributyltin oxide (No. 14, 1999)... 

The excess of bromine is removed by warming the acidic solution gently till the vapours show a negative test with starch-iodide paper. However, the residual traces of Br2 are reduced by treatment of the resulting solution with phenol to yield the corresponding 2,4,6-tribromophenol as shown below ... 

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 ... 

Kinetic studies of the oxidation of aspirin by bromamine-T, A-bromosuccinimide (NBS), and A-bromophthalimide (NBP) support a mechanism in which the unpro-tonated oxidant is the active species. " The ultimate product of the reaction is 2,4,6-tribromophenol, which arises through decarboxylation, bromination and loss of acetic acid. The NBP and NBS oxidations of -hydroxy acids are found to be similar in mechanism. 

Benzenediazonium Tribromide (Diazobenzene Tribromide), CsHs.N2.Br3 mw 264.95, N 10.58% orn-red ndls, mp 63-5°(dec), expl weakly on heating diffc sol in cold ale insol in w or erh. Can be prepd by treating a benzenediazonium chloride soln with an aq K bromide soln and by reacting bromine in a hydrobromic acid soln with a soln of benzenediazonium nitrate or sulfate. The dry comp is stable but in a humid atm it dec into 2,-4,6-tribromophenol. It rapidly dec in the presence of ale... 

When treated with bromine water an aqueous solution of phenol gives an immediate precipitate of 2,4,6-tribromophenol (Section 9.6.6, p. 1251), owing to the powerfully activating influence of the negatively charged oxygen in the phenoxide ion. 

The presence of the hydroxyl group in phenols facilitates the substitution of the nuclear hydrogen atoms by halogen the number and position of the substituent atoms varies with the nature of the phenol. This method is an indirect means of identification, as the formation of a substitution derivative is not a characteristic reaction of the phenol group but of the benzene nucleus. Phenol reacts with bromine to give 2,4,6-tribromophenol ... 

Electrophilic attack of bromine on 2,4,6-tribromophenol leads to a cationic intermediate. 

Phenols — Electron -capture Phenols first brominated to tribromophenol — [244- 245]... 

Electrophilic substitution is helped by the phenol group that acts as an activating group and directs substitution to the ortho and para positions. Sulphonation and nitration of phenols are both possible to give ortho and para substitution products. Sometimes the phenolic groups can be too powerful an activating group and it is difficult to control the reaction to one substitution, e.g., the bromination of phenol leads to 2,4,6-tribromophenol even in the absence of a Lewis acid ... 

Dibromo-4-nitrophenol has been prepared by the nitration of 2,6-dibromophenol1 or of dibromophenol sulfonic acid,2 and by the action of nitric acid on 2,6-dibromo-4-nitroso-phenol3 or on 2,4,6-tribromophenol.4 It has been obtained from the corresponding ethyl ether 5 and by the action of bromine on />-nitrosophenol,6 4,6-dibromo-2-nitrophenol,7 5-nitro-2-hydroxy-benzoic acid,8 and 5-nitro-2-hydroxybenzenesulfonic acid.9 The dibromination of />-nitrophenol I0>13 has been carried out in sulfuric acid solution 11 and in the presence of aluminum chloride.12 The method described here is essentially that of M"hlau and Uhlmann.13... 

Reaction of phenols with BTMABr3 or TBABr3 in a methanol/methylene chloride solvent mixture results in a step-by-step bromination. The degree of bromination depends solely on the molar ratio of reagent to substrate (equation 64)522. With the first mole of reagent / -bromophenol is obtained, followed by 2,4- dibromophenol and, finally, 2,4,6-tribromophenol. The role of methanol in these systems is apparently the in situ formation of methyl hypobromite. The same selectivity is, however, found in chloroform523. 

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