A 3-l. round-bottomed three-necked flask is equipped with a mechanical stirrer, a 500-ml. dropping funnel, and a 250-ml. dropping funnel. The flask is contained in a pneumatic trough through which water at room temperature is circulated. A mixture of 30 ml. of ethyl cyanoacetate and 100 ml. of ethanol is placed in the flask. Meanwhile 54 g. (0.5 mole) of p-benzoquinone in a 1-l. flask is heated to 40° with 500 ml. of 95% ethanol, and, when practically all the quinone is dissolved, 56 g. (0.5 mole) of ethyl cyanoacetate is added and the mixture is stirred until solution is complete (Note 1). Most of this solution is placed in the 500-ml. dropping funnel, the remainder being added when the funnel becomes sufficiently emptied after the reaction has started.

Twenty-five milliliters of concentrated ammonium hydroxide (Note 2) is introduced into the 3-l. flask. A solution of 100 ml. of concentrated ammonium hydroxide in 150 ml. of water is placed in the 250-ml. dropping funnel, which is loosely stoppered. Stirring is started, and the stopcocks of the two dropping funnels are adjusted so that the solutions will be delivered into the flask at a uniform rate in a period of about 45 minutes (Note 3). Stirring is continued for an additional 10 minutes. The mixture is then permitted to stand for 1 hour, after which the purplish red precipitate is filtered with suction. Any solid material adhering to the walls of the flask is washed onto the funnel with ethanol. The solid is then washed three times on the funnel with ethanol (Note 4). The filtrate and washings are discarded. The product is slightly impure diethyl α,α'-dicyano-2,5-dihydroxy-p-benzenediacetate and weighs 36–41 g. (43–49%) (Note 5).

For the hydrolysis, 36 g. (0.11 mole) of the residue is transferred to a 1-l. round-bottomed flask equipped with a reflux condenser, and 210 ml. of concentrated hydrochloric acid in 190 ml. of water is added. The mixture is refluxed gently at first, then vigorously (Note 6), until hydrolysis is essentially complete (about 20 hours). Then 180 ml. of water and 4 g. of Norit A are added and the mixture is stirred and boiled for 3 minutes, after which it is rapidly filtered with suction through two layers of hardened filter paper in a Büchner funnel (Note 7). The filtrate, upon cooling to 20° or below, deposits 18 g. (72%) of lightly colored 2,5-dihydroxy-p-benzenediacetic acid (Note 8). A snow-white product is obtained by dissolving 18 g. of this material in 375 ml. of boiling water, treating with 2 g. of Norit A, and filtering. Upon cooling, there is deposited 15 g. (61%) of the acid which melts at 233° (Note 9).