Aquabis ethylenediamine hydroxochromium III Dithionate

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 c/s-[aquabis(ethylenediamine)hydroxochromium(III)] dithionate salt is stable for years. It is insoluble in water but very soluble in strong acid and strong base, giving the corresponding m-diaqua and m-dihydroxo species. The crude product is used in the preparation of m-[diaquabis(ethylenediamine)chromium-(III)] bromide (Sec. G) and of di-/a-hydroxobis[bis(ethylenediamine)chromium-(III)] dithionate (Sec. J). 

Starting material. The preparation given below is based on an improved method. Here the bromide salt is obtained from crude c/s-[aquabis(ethylene-diamine)hydroxochromium(III)] dithionate (Sec. F) by treatment with hydro-bromic acid. The pure c/s-[diaquabis(ethylenediamine)chromium(IIl)] bromide is used to prepare pure cfs-[aquabis(ethylenediamine)hydroxochromium(III)] dithionate (Sec. F). 

In the procedure given here tfie dithionate is obtained almost quantitatively from cis- [aquabis(ethylenediamine)hydroxochromium(III)] dithionate by refluxing in acetic anhydride, following the method given in the literature. The preparation of as-[aquabis(ethylenediamine)hydroxochromium(III)] dithionate is given in Section F. 

Crude ds-[aquabis(ethylenediamine)hydroxochromium(III)] dithionate (40.0 g, 0.109 mole) (see Sec. E) is added to 400 mL of acetic anhydride. The suspension is heated to reflux within 20 minutes, kept at reflux for another 20 minutes, and then cooled in an ice bath. The sample is filtered, washed with two 50-mL portions of 96% ethanol, five 50-mL portions of 2 M acetic acid, and four 100-mL portions of 96% ethanol, and then thoroughly washed with diethyl ether. By the washing with acetic acid, a small amount of unreacted ds-[aqua-bis(ethylenediamine)hydroxochromium(III)] dithionate is removed. Drying in air yields 34.5 g (91%) of a nearly pure product. The crude dithionate is used in the syntheses of the chloride and the bromide, as given below. The pure dithionate is obtained from the pure bromide by the following procedure. 

Methods for preparation of ds-[tetraammineaquachlorochromium(III)] sulfate, ds-[tetraammineaquahydroxochromium(III)] dithionate monohydrate, and ds-[tetraammineaquahydroxocobalt(III)] dithionate monohydrate as nearly pure intermediates are given. The preparation of crude dx-[aquabis(ethylenediamine)-hydroxochromium(lll)] dithionate and a method for obtaining the pure salt are given. These dx-aquahydroxo salts have been used to prepare the following pure dx-diaqua salts dx-[tetraamminediaquachromium(Ill)] perchlorate, dx-[tetra-amminediaquacobalt(lll)] perchlorate, and dx-[diaquabis(ethylenediamine)-chromium(lll)] bromide dihydrate. 

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