Hydrochloric Acid → 5,6-Dichloro-2,3-dicyanopyrazine

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FIG. 13 shows the reaction pathway. This reaction should be carried out in a fume hood. In a 500 mL round-bottomed flask with a 24/40 ground-glass joint attached to an efficient reflux condenser and under a nitrogen atmosphere, a magnetically stirred slurry consisting of 8.10 g (0.050 mol) of 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, 4.0 mL of dimethylformamide 306 and 160 mL of thionyl chloride 1301 was heated. Gas evolution began at ca. 62° [SO2 & HCl gasses evolved]. After about 3.5 hours, the solid had dissolved and the temperature had risen to 70°. After cooling to room temperature, a Dry Ice/acetone bath was applied until the temperature of the reaction medium was −65°. The crystals which formed were collected by rapid filtration of the cold slurry through a sintered-glass filter under a nitrogen blanket. The solid was washed twice with 150-ml portions of cold diethyl ether and air-dried to give 7 g (70%) of 2,3-dichloro-5,6-dicyanopyrazine 301, mp 180-182°. Crystallization of the product may be accomplished if dark, from ˜50 mL of chloroform with carbon treatment to give 5.5 g of purified product.

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