In a
1-l. flask fitted with a
mechanical stirrer and a
dropping funnel are placed
46.2 g. (0.3 mole) of 2,4-dihydroxybenzoic acid (β-resorcylic acid, p. 557) and
350 cc. of glacial acetic acid. After the stirrer is started the mixture is warmed until solution results (45°) and then is allowed to cool to 35°. Through the dropping funnel is added a solution of
48 g. (15 cc., 0.3 mole) of bromine in
240 cc. of glacial acetic acid with vigorous stirring over a period of about one hour. The temperature of the reaction mixture remains at 30–35°. When all the
bromine is added the solution is poured into 5 l. of water, and the mixture is cooled to 0–5° and allowed to stand for several hours. The fine, white crystals of
2,4-dihydroxy-5-bromobenzoic acid are collected on a
10-cm. Büchner funnel and washed with about 500 cc. of cold water. The crude product, after air drying at room temperature, melts at
194–200° and weighs
55–60 g. For purification it is dissolved in 1.5 l. of boiling water, and the solution is refluxed for one hour (Note
1), filtered while hot, and cooled in an
ice bath. The material which crystallizes is collected, washed with 100 cc. of cold water, and air dried. The yield of colorless
2,4-dihydroxy-5-bromobenzoic acid, melting at
206.5–208.5° (corr.), is
40–44 g. (
57–63 per cent of the theoretical amount).
Thirty grams of purified 2,4-dihydroxy-5-bromobenzoic acid is refluxed for twenty-four hours with 375 cc. of water, and the resulting solution is filtered, cooled, and extracted with a
400-cc. and a 200-cc. portion of ether. The
ether is removed by evaporation, and the
4-bromoresorcinol is dried on a
steam bath. The yield of product melting at
100–102° (Note
2) is
22–22.5 g. (
90–92 per cent of the theoretical amount).