Anhydrous Chromium III Sulfate

The method outlined here is similar to the latter but obviates the separation of potassium sulfate from the product. The new methods described below for obtaining various tris (ethylenediamine) chromium(III) salts with anhydrous chromium(III) sulfate as the starting material can be used also for preparing the corresponding propylenediamine derivatives.  

Hydrated chromium(III) sulfate is dehydrated by heating for several days in an oven at 100 to 110°. The material, originally lumpy, can be groimd to a powder after the first 2 or 3 days and then returned to the oven for further drying. Dehydration is complete when the powder fails to dissolve in water. 

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This material is prepared exactly as described for the corresponding ethyienediamine salt, using 30ml of pn and 21g of anhydrous chromium (III) sulfate. 

Rollinson andBailar prepared hexamminechrOmium,(III) nitrate in low yield by treating anhydrous chromium (III) sulfate with liquid anunonia in the presence of ammonium nitrate. They also prepared the hexammine by dissolving chloropentamminechromium(III) nitrate in liquid ammonia containing a little sodium amide. The following procedure utilizes the observation of Rollinson and Bailar that sodium amide (a base in liquid ammonia) catalyzes the ammona-tion of the chloropentamminechromium(III) ion. 

No reaction was observed when 86.5g of anhydrous di-propylenetriamine were heated with 27g of dehydrated chromium (III) sulfate on the steam bath. There was no sign of decomposition even after 4 hours at 2G0°C. A drop of water added as catalyst made no difference. 

Chromium oxychloride, formation of, by CrCl2, 1 126 Chromium(II) salts, 6 144 Chromium (III) sulfate, anhydrous, 2 197... 

If tri8(ethylenediamine)chromium(III) chloride is prepared by the method of Rollinson and Bailar,7 it is worthy of note that if the dehydration of the hydrated chromium (III) sulfate is performed in a vacuum oven (2-3 mm. Hg, 70-80°C.) the anhydrous sulfate is obtained in a much more reactive form so that the reaction with ethylenediamine, when started by local heating, proceeds by itself and is finished within an hour. Editor s note For an alternative preparation, see Inorganic Syntheses, 10, 33 (1967) also ref. 26. 

About 800 ml. of liquid ammonia is introduced into a 1-1. Dewar flask, or a 1000-ml. beaker that is placed within a 1500-ml. beaker, and 0.5 g. of clean sodium metal and 0.2 g. of iron(II) ammonium sulfate are added. After the blue color of the sodium has disappeared, 50 g. (approximately 0.3 mol) of anhydrous chromium(III) chloride is added in 2-g. portions, while the solution is constantly stirred. After the addition has been completed (1 to 2 hours), the brown precipitate is allowed to settle, and the clear, slightly colored supernatant liquid is decanted from the beaker or siphoned from the Dewar flask. 

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