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2,3-Dicyano-5,6-dichlorohydroquinone (10 g) was suspended in a solution of ethanol (40 ml) and 5% hydrochloric acid (110 ml) contained in a stoppered Erlenmeyer flask. Benzene (220 ml) was added, followed by lead dioxide (44 g), and the contents of the flask shaken vigorously by hand for 5 minutes. The emulsion was then filtered through a Buchner funnel containing a layer of celite, and the residue washed with benzene. The combined filtrates were transferred to a separating funnel, the aqueous layer removed, and the organic phase washed twice with a small quantity of water. Concentration of the dried benzene solution yielded red crystals of the quinone, and precipitation was completed by the addition of light petroleum (30—60°). The solid was separated by filtration and washed with a little petrol. When dry the quinone was yellow and melted at 206—209° (lit. m.p. 203°). The yield mas 8.3 g (83%).
5,5,6,6-Tetrachloro-2,3-dicyanocyclohex-2-ene-1,4-dione (1 g), m.p. 130—131°, was dissolved in benzene (20 ml) and the solution refluxed for 40 minutes with activated charcoal (1 g). The solution was filtered and the orange-red-colored filtrate concentrated to about 10 ml, when red crystals separated. These were removed and washed with a little n-hexane. The dried material weighed 0.55 g (73%) and had m.p. 210—213°. It crystallized in long amber-colored needles from chloroform, m.p. 215—217°.
Calc. for C8N2O2Cl2: Cl, 31.25; N, 12.34. Found: Cl, 31.71, 31.88; N, 11.88, 11.81.
Infrared (CHCl3): C=O at 1696 cm-1, C=C at 1560 cm-1, strong band at 1175 cm-1, C?N at 2240 cm-1.
Ultraviolet: λmax at 238 nm (ε 11,950); 257 nm (ε 10,700); 290 nm (ε 8,900); 345 nm (ε 1,360); 482 nm (ε 870).
The mixture (15 g), which was obtained by the lead dioxide oxidation of an incompletely chlorinated sample of 2,3-dicyano-5,6-dichlorohydroquinone and contained 2,3-dicyanoquinone, 5-chloro-2,3-dicyanoquinone, and D.D.Q., was dissolved in acetic acid (50 ml) and chlorinated at reflux temperature for 30 minutes. A small quantity of solid (1.7 g), identified as dicyanodichlorohydroquinone, was separated from the cooled solution, which was then evaporated in vacuo. The residue was crystallized from benzene and gave 7.5 g of the tetrachloro compound, m.p. 130—132°. The filtrate was diluted with benzene (50 ml) and refluxed with charcoal (5 g) for 30 minutes. The resulting orange solution, after filtration and evaporation, yielded 4.5 g of D.D.Q., m.p. 213—215°.
A slurry of 2,3-dicyanohydroquinone (5 g., 0.031 mole) in water (35 g.) and concentrated hydrochloric acid (35 ml.) was treated over 45 min. with concentrated nitric acid (9.4 g. of 70%, 0.15 mole) at a temperature of 35±3°. The mixture, which foamed initially, turned yellow. After all the nitric acid had been added, the yellow suspension was stirred for 1 hr., filtered, washed with carbon tetrachloride, and dried, yield 6.4 g. (90%), m.p. 212—213° (lit. m.p. 213—215°). The infrared spectrum and elemental analysis were consistent with expectation. Reduction of DDQ with aqueous sodium bisulfite gave 2,3-dichloro-5,6-dicyanohydroquinone, mol. wt. 229.3 (calcd. 229).
© Collected Ruslan Anatolievich Kiper, burewestnik@mail.ru