(CAS NO.: ), with other names like , diethyl ester, could be produced through many synthetic methods.

A. (II) sulfate solution. A 3-l., three-necked flask fitted with a gastight mechanical stirrer and nitrogen inlet and outlet stopcocks is charged with 300 g. (ca. 0.55 mole) of hydrated chromium(III) sulfate, 2 l. of distilled water, 75 g. (1.15 g. atoms) of mossy zinc, and 4.0 ml. (54 g., 0.27 g. atom) of mercury. After the flask has been flushed with nitrogen for 30 minutes, the mixture is warmed in a water bath to about 80°with stirring for 30 minutes under a nitrogen atmosphere to initiate reaction. Then the mixture is stirred at room temperature under a nitrogen atmosphere for an additional 30 hours, at which time the originally green reaction mixture has been converted to a clear, deep blue solution. While a nitrogen atmosphere is maintained over the reaction solution, the mechanical stirrer is removed and replaced with a nitrogen outlet. The third neck of the reaction flask is fitted with a short adapter closed with a rubber septum.

The solution is standardized by withdrawing 5.0-ml. aliquots into a hypodermic syringe fitted with a relatively wide-bore needle and flushed with nitrogen before use. The aliquots are quenched by injecting them into 10 ml. of aqueous 1M ferric chloride solution in an Erlenmeyer flask under a nitrogen atmosphere. After 2 minutes the flow of nitrogen is stopped, and the resulting solution is diluted with 50 ml. of water and titrated with 0.1N ceric sulfate to the ferrous ion-phenanthroline end point. Solutions prepared in this fashion are usually 0.55M in chromium(II) species and are stable for years, if they are protected from reaction with oxygen.

B. Reduction of diethyl fumarate (CAS NO: ). A 1-l. three-necked flask is equipped with a magnetic stirring bar, an addition funnel with a pressure-equalizing tube, a stopcock connected to a mercury trap, and a rubber septum. The addition funnel is charged with a solution of 13.87 g. (0.080 mole) of diethyl fumarate in 137 ml. of dimethylformamide. A nitrogen line is connected to the top of the addition funnel and the system is thoroughly flushed with nitrogen. With a hypodermic syringe, 318 ml. (0.175 mole) of the previously described 0.55M chromium(II) sulfate solution (0.175 mole) is added to the reaction flask through the rubber septum. After the stirrer has been started, the diethyl fumarate solution is added rapidly. The solution immediately turns green and the reduction is complete in 10 minutes. The resulting solution is diluted with 100 ml. of water and 30 g. of ammonium sulfate is added. The mixture is shaken with four 150-ml. portions of ether, and the combined ether extracts are washed with three 50-ml. portions of water and then dried over magnesium sulfate. After the ether has been removed by distillation through a 60-cm. Vigreux column, the residual liquid is distilled through a short Vigreux column to separate 12.4–13.2 g. (88–94%) of diethyl succinate; b.p. 129° (44 mm), n²³D 1.4194.