2- Bromophenols

Considerable attention has been directed to regiospecific monobromination in which bromine has been used often in conjunction with another component. 

These reactions have been summarised in Table 8.3 (refs.21-28) and often indicate the known more selective nature of bromination compared with chlorination. 

A 2-bromophenol derivative has been obtained in 90% yield from the reductive aromatisation of 2-bromo-4-hydroxycyctohexa-2.5-dienones by treatment over 2 hours with sodium hydrosulphite in tetrahydrofuran/water (3 1) (ref.29). 

Due to their activation the preparation of nuclear monobromo methylphenols can be unexpectedly complicated. The use of polybromophenols to obtain simpler phenols such as 4-bromo-3-methylphenol, 3-bromo and 3,5-dibromo- 

4-methylphenol, 3-bromo and 3,5-dibromo-2-methylphenol from the corresponding methylphenols, by the action of 55% hydriodic ackJ, has been described (ref.30). 

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Moat phenols are crystalline solids notable exceptions are m-cresol and o-bromophenol. The monohydric phenols generally have characteristic odours. The solubihty in water increases with the number of hydroxl groups in the molecule. 

Thus o-hydroxyphenyl-llthium cannot be obtained from o-bromophenol and lithium but, under proper conditions, o-bromophenol reacts with n-butyl-lithium to give a good yield of the lithium salt of o-hydroxyphenyl-hthium. An interesting application is to the preparation from m-bromochlorobenzene and M-butyl-lithlum of w-chlorobenzoic acid—an expensive chemical ... 

By condensing o sulphobenzoic anhydride with phenol in the presence of anhydrous zinc chloride, phenolsulphonephthalein (phenol red) is formed. Tetrabromination of the latter afibrds tetrabromophenolsulphonephthalein (bromophenol blue) ... 

Intermediates benzene to nitrobenzene to m bromonitrobenzene to m bromoanihne to m bromophenol Reagents HNO3 H2SO4 Br2 FeBr3 Fe HCl then HO NaN02 H2SO4 H2O then heat in H2O... 

Bromophenol blue 2, 7 -DichIorofluorescein Eosin, tetrabromofluorescein Fluorescein Potassium rhodizonate, C404(0K)2 Rhodamine 6G Sodium 3-aIizarinsuIfonate Thorin Dissolve 0.1 g of the acid in 200 mL 95% ethanol. Dissolve 0.1 g of the acid in 100 mL 70% ethanol. Use 1 mL for 100 mL of initial solution. See Dichlorofluorescein. Dissolve 0.4 g of the acid in 200 mL 70% ethanol. Use 10 drops. Prepare fresh as required by dissolving 15 mg in 5 mL of water. Use 10 drops for each titration. Dissolve 0.1 g in 200 mL 70% ethanol. Prepare a 0.2% aqueous solution. Use 5 drops per 120 mL endpoint volume. Prepare a 0.025% aqueous solution. Use 5 drops. 

Halophenols without 2,6-disubstitution do not polymerize under oxidative displacement conditions. Oxidative side reactions at the ortho position may consume the initiator or intermpt the propagation step of the chain process. To prepare poly(phenylene oxide)s from unsubstituted 4-halophenols, it is necessary to employ the more drastic conditions of the Ullmaim ether synthesis. A cuprous chloride—pyridine complex in 1,4-dimethoxybenzene at 200°C converts the sodium salt of 4-bromophenol to poly(phenylene oxide) (1) ... 

The oxidation of 4-bromophenols to quinones can also be accompHshed using periodic acid (113). A detailed study of this reagent with stericaHy hindered phenols provided insight about the quinonoid product (114). The highest yield of 2,6-di-/-butyl-l,4-ben2oquinone [719-22-2] is for the case of R = OCH. The stilbene stmcture [2411-18-9] is obtained in highest yield for R = H. 

A double end point, acid—base titration can be used to determine both sodium hydrosulfide and sodium sulfide content. Standardized hydrochloric acid is the titrant thymolphthalein and bromophenol blue are the indicators. Other bases having ionization constants in the ranges of the indicators used interfere with the analysis. Sodium thiosulfate and sodium thiocarbonate interfere quantitatively with the accuracy of the results. Detailed procedures to analyze sodium sulfide, sodium hydro sulfide, and sodium tetrasulfide are available (1). 

A good technical grade of carbon tetrachloride contains not more than the following amounts of impurities 1 ppm acidity as HCl, 1 ppm carbon disulfide if manufactured by carbon disulfide chlorination, 20 ppm bromine, 200 ppm water, and 150 ppm chloroform. The residue should not exceed 10 ppm on total evaporation. The product should give no acid reaction with bromophenol blue, and the starch iodine test should indicate the absence of free chlorine. 

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