Preparation of Bromophenols

Bromine is a hazardous chemical that may cause serious chemical bums. Do not breathe its vapors or allow it to contact your skin. Perform all operations involving the transfer of solutions of bromine in a hood wear latex gloves when handling this chemical. If you get bromine on your skin, immediately flood the area with warm water and soak the skin in 0.6 Af sodium thiosulfate solution for up to 3 h if the burn is particularly serious. 

Do nofuse acetone to rinse glassware containing residual bromine. This prevents formation of a-bromacetone, a severe lachrymator. Rather, follow the procedure described in Wrapping It Up. 

Preparation Sign in at www.cengage.com/logln to read the MSDSs for the chemicals used or produced in this procedure. 

A stock solution for bromination in this preparation should be supplied if not, prepare it by dissolving 1 g of potassium bromide in 6 ml of water and adding 1 g of bromine. Dissolve 0.5 g of the phenolic compound in water or 95% ethanol, and add the bromine-containing solution to it dropwise. Continue the addition until the reaction mixture begins to develop a yellow color, indicating the presence of excess bromine. Let the mixture stand for about 5 min if the yellow coloration begins to fade, add another drop or two of the solution of bromine. Add 5 mL of water to the mixture and then a few drops of 0.5 M sodium bisulfite solution to destroy the excess bromine. Shake the mixture vigorously, and remove the solid derivative by vacuum filtration. If necessary, neutralize the solution with concentrated hydrochloric acid to promote precipitation of the derivative. Purify the solid by recrystallization from 95% ethanol or aqueous ethanol. 

One of the best qualitative tests for the carboxylic acid group is solubility in basic solutions. Carboxylic acids are soluble both in 1.5 M sodium hydroxide solution and in 0.6 M sodium bicarbonate solution, from which they are regenerated by acidification. Solubility properties are discussed in Section 25.3. 

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