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).