A. Ethyl oxalylsuccinate. Potassium (39.5 g., 1 gram atom) is cut into pieces under xylene (Note 1) in a wide evaporating dish. The xylene is poured off, and the metal is washed with three 50-ml. portions of absolute ether. The potassium is then transferred quickly to a 2-l. three-necked flask containing 650 ml. of anhydrous ether and fitted with a reflux condenser, a mercury-sealed mechanical stirrer (Note 2), and a dropping funnel containing 150 ml. of anhydrous ethanol. The ethanol is added over a period of about 1.5 hours; stirring is unnecessary. After most of the ethanol has been added, the flask is heated on a water bath to ensure complete solution of the potassium. This usually takes from 3 to 4 hours. After the reaction is completed, the flask is cooled to room temperature, and 146 g. (1 mole) of ethyl oxalate is added rapidly through the dropping funnel, with stirring, to the solution of potassium ethoxide in ether. A yellow color develops at this point. The stirring is continued for an additional 10 minutes. Then 174 g. (1 mole) of ethyl succinate is added rapidly, with vigorous stirring (Note 3). After a few minutes, the potassium salt crystallizes, making further stirring impracticable. It is collected on a filter and washed with ether until the salt is colorless.

The salt is dissolved in 270 ml. of water, and 100 ml. of concentrated hydrochloric acid is added. The ethyl oxalylsuccinate separates as an oil and rises to the surface. It is removed by extracting the mixture with 100-ml. portions of ether until the aqueous solution is almost colorless. The extracts are dried over sodium sulfate, and the ether is distilled under reduced pressure. The ethyl oxalylsuccinate remains in the flask as a yellow oil. The yield is 225–227 g. (82–83%) (Note 4).

B. α-Ketoglutaric acid. The ester obtained by the foregoing procedure is mixed with 600 ml. of concentrated hydrochloric acid and left overnight. The mixture is concentrated by distillation (Note 5) until the temperature of the liquid reaches 140°. It is poured into an evaporating dish and allowed to cool. The solid mass, weighing 110–112 g., is then pulverized. The yield of α-ketoglutaric acid is 92–93% of the theoretical for the last step, or 75–77% based upon diethyl succinate. The light-tan product, obtained as described above, is suitable for most purposes, but a purer acid, m.p. 109–110° (cor.), may be obtained by recrystallization from an acetone-benzene mixture.