In a 2-l. round-bottomed flask are placed 218 g. (1 mole) of p-hydroxyphenylarsonic acid (Note 1) and 375 cc. of water. A solution of 180 g. (4.5 moles) (Note 2) of sodium hydroxide in 375 cc. of water is added, and the mixture shaken until a homogeneous solution is obtained. After cooling to 40–50° there is added 189 g. (2 moles) of chloroacetic acid in small portions (Note 3) with stirring, and the clear solution is refluxed for four hours. At the end of this time the mixture is cooled to 20°, filtered to remove a slight flocculent precipitate, and the p-arsonophenoxyacetic acid precipitated (Note 4) by the addition of 200 cc. (2.1 moles) of hydrochloric acid (sp. gr. 1.19).

The product is filtered on a 10-cm. Büchner funnel and washed with three successive 100-cc. portions of cold water. It is then crystallized from 2 l. of hot water (Note 5), filtered, and washed twice with 100-cc. portions of cold water, once with 25 cc. of acetone, and once with 25 cc. of ether. After drying at 110° for one hour, there remains a pure white, anhydrous product weighing 110–120 g. (40–43 per cent of the theoretical amount) (Note 6). An arsenic analysis shows the product to be about 99 per cent pure.