Phenol reaction with bromine

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. 

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 ... 

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 ... 

Phenols are highly activated towards electrophilic attack, which occurs readily at the 2- and 4-positions. For example, phenol reacts with bromine at room temperature in ethanol and in the absence of a catalyst to give 2,4,6-tribromophenol. Other electrophilic substitution reactions such as nitration, sulfonation, Friedel-Crafts, chlorination and nitrosation also proceed readily and hence care is needed to ensure multisubstitution does not occur. Protection of specific ring positions can also prevent unwanted substitution. Relatively mild conditions are usually employed. 

AMSPEC-KR (1309-64-4) Ignites and burns in heated air above 420°F/215°C. Violent reaction with bromine trifluoride. Reacts with chlorinated rubber, alcohols/glycols, organic and a-hydroxy acids (fruit acids), o-dihydric phenols, polyethylene glycol, and other polyhydroxy compounds. 

The use of acetic anhydride for the acetylation of phenols has been described in some papers [86,87]. Determination of chlorophenols in freshwater, wastewater, and seawater using acetylation and BCD was reported by Abrahamsson and Xie [87]. They compared two derivatization procedures, pentafluorobenzoylation versus acetylation, and concluded that the acetylated derivatives gave better separation on the capillary column. Derivatization using heptafluorobutyryl in combination with GC-BCD [88] involves an extraction of the acidified sample into benzene before derivatization. Another method describes the conversion of eight phenols (phenol, cresols, and xylenols) into corresponding bromophenols after reaction with bromine followed by an analysis using GC-BCD [91 ]. 

Me3SiCH2CH=CH2i TsOH, CH3CN, 70-80°, 1-2 h, 90-95% yield. This silylating reagent is stable to moisture. Allylsilanes can be used to protect alcohols, phenols, and carboxylic acids there is no reaction with thiophenol except when CF3S03H is used as a catalyst. The method is also applicable to the formation of r-butyldimethylsilyl derivatives the silyl ether of cyclohexanol was prepared in 95% yield from allyl-/-butyldi-methylsilane. Iodine, bromine, trimethylsilyl bromide, and trimethylsilyl iodide have also been used as catalysts. Nafion-H has been shown to be an effective catalyst. 

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 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... 

For large scale work the cost of the resin might be a major disadvantage unless it could be recovered. We have therefore taken a sample of resin filtered off after a reaction and reconverted it into the tribromide by addition of bromine. Reuse of this resin in a further reaction with phenol gave results which were very comparable with those obtained using the original resin. Therefore, recycling of the resin appears to be a viable possibility. 

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