Fifty grams (0.29 mole) of sulfanilamide is dissolved in a mixture of 850 ml. of water and 100 ml. (0.68 mole) of 40% hydrobromic acid. The solution is heated as above but to 70–75° and 65 g. (59 ml., 0.58 mole) of 30% hydrogen peroxide is added. A precipitate settles in 2–3 minutes, and the solution becomes yellow. The heat of the reaction causes the internal temperature to rise without further application of heat to a maximum of 85–90℃ after 10 minutes; by the end of the reaction time, the temperature will have fallen to about 70℃. After a total reaction time of 30 minutes, when the mixture has become almost solid and is very difficult to stir, the material is filtered hot. The yield of 3,5-dibromosulfanilamide is 85–90 g (90–94%), and the crude tan product melts over a range of 1–2° in the region 230–237℃.
