The crude acetonedicarboxylic acid from 700 g. (3.64 moles) of citric acid, as described on p. 10, is treated with 700 g. (882 cc.) of absolute ethyl alcohol (pp. 249 and 259) (Note 1) to which has been added at least 130–150 g. of dry hydrogen chloride (p. 293). The mixture is placed in a flask fitted with a stopper holding a calcium chloride tube and then is heated to 45°. It is kept in a water bath at 45° (bath temperature) with frequent shaking until all the acid is dissolved (fifteen to twenty minutes). The solution is allowed to cool down to room temperature in the bath and finally to stand about twelve hours (Note 2).

The contents of the flask are then poured into 1300–1400 cc. of ice water, the ester layer separated, and the water-alcohol layer extracted twice with 700-cc. portions of benzene. The benzene extracts are added to the original ester, which has been separated. The total solution thus obtained is washed with about 400 cc. of 10 per cent sodium carbonate solution to remove the acid, then once with dilute sulfuric acid, and finally twice with 400-cc. portions of water (Note 3). The benzene is distilled on a water bath, and the ester is distilled under reduced pressure. A small low-boiling fraction comes over first, and then the ester, which boils at 131–136°/9–10 mm. or 145–148°/17 mm. (Note 4). The yield of product amounts to 284–315 g. (39–43 per cent of the theoretical amount based on the citric acid).