Sodium dithionate.dihydrate

The pure salt is obtained by the following method from pure cis- [diaquabis-(ethylenediamine)chromium(III)] bromide dihydrate. [Diaquabis(ethylenedi-amine)chromium(III)] bromide dihydrate (2.00 g, 0.00413 mole) (see Sec. G) is dissolved at 0° in 5.00 mL of 0.100 jW hydrochloric acid. To this solution is added a solution of 1.10 g (0.00454 mole) of sodium dithionate dihydrate in 10 mL of water at room temperature. To the filtered solution is added, with stirring and cooling in an ice bath, 23.0 mL of 0.200 M sodium hydroxide. Precipitation of red crystals of cis- [aquabis(ethylenediamine)hydroxochromium(III)] dithionate commences almost instantaneously. After a few minutes the sample is filtered and washed thoroughly with water, 96% ethanol, and then diethyl ether. Drying in air yields 0.9 g (59%) of pure ds-[aquabis(ethylenediamine)hydroxochrom-ium(III)] dithionate. Found Cr, 14.04 N, 15.16 C, 13.17 H, 5.23. 

The pure dithionate is obtained from the crude product by reprecipitation as follows Crude dithionate (2.0 g, 0.00478 mole) and finely powdered sodium dithionate dihydrate (2.4 g) are stirred together in 12.0 mL of 0.50 M hydrochloric acid in a 50-mL conical flask at room temperature until all is dissolved. The solution is filtered through a fine-porosity 3-cm sintered glass funnel into a 100-mL suction flask, and 6.0 mL of 1.0 Af sodium hydroxide is added dropwise with stirring. A pale yellow precipitate forms rapidly, and after stirring at room temperature for 15 min the mixture is kept in an ice bath for 45 min and the product is isolated as before. Yield 1.88 g (94%). The product reprecipitated in this manner is pure. 

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