Exercise 10. Cuprous Chloride

The general scheme of preparation is to treat any cupric salt in solution (cupric ion) with concentrated hydrochloric acid and a reducing agent, preferably metallic copper. Powder about 50 g. of crystallized 

Pour the hot solution into at least 21. of cold water to which a few grams of sodium sulfite has been added and allow the white crystalline powder to settle. The water should contain a little sodium sulfite or sulfur dioxide, which will tend to prevent oxidation. Wash the precipitate several times by decantation, the wash water in each case containing sulfur dioxide and made acid with hydrochloric acid. Finally, collect the precipitate on a small Witte plate provided with a close-fitting filter paper, washing it on to the plate with portions of the filtrate and taking care not to let all the liquid drain through the filter, exposing the moist compound to the air. 

Have at hand 50 cc. of glacial acetic acid. Turn on the pump, and when the water just sucks through the 

Topics Cuprous salts of oxygen acids, Daniels, J. Am. Chem. Soc., 37, 1167 (1915) Sloan, ibid., 32, 972 (1910). 

Additional Exercises Cuprous sulfite, Cu2S03, Groger, Z. anorg. Chem., 28, 154 (1901). 

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Prelab Exercise Write a balanced equation forthecoupling of 2-methyl-3-butyn-2-ol. What role does cuprous chloride play in this reaction ... 

Alternative Method.—Cupric chloride would serve better than a mixture of salt and copper sulfate, but it is much more expensive. A still simpler way is to start with copper. Place a suitable quantity in a flask and add concentrated hydrochloric acid in the ratio given in the last exercise. Heat nearly to boiling and add concentrated nitric acid drop by drop through a separatory funnel. When most of the copper has dissolved, stop adding nitric acid, heat vigorously for a time, and pour into cold water containing sodium sulfite. Proceed as in the first method. The aqua regia converts some of the copper into cupric chloride, and this is reduced to the cuprous salt by the excess of copper. 

Great care should be exercised in these preparations, in order to exclude traces of moisture. To a stirred solution of the alkyne (6 mmol) in dichloromethane (50 ml) was added butyl lithium (2.4 ml of a 2.5 M solution in hexane) at - 70°C, under a positive pressure of nitrogen. After 10 min, cuprous cyanide (0.27 g, 3 mmol) was added and stirring continued for 2 h at — 40°C. The mixture was cooled to - 70°C and the iodonium salt (1 mmol) was added this mixture was allowed to warm to room temperature slowly and stirred for another 10 h. Then it was poured into a saturated aqueous solution of ammonium chloride (100 ml), extracted with dichloromethane and the organic layer was dried and concentrated. The residue was purified by filtration through a short silica column (hexane, then dichloromethane) solvent evaporation afforded pure bicyclic enediynes, in 36-69% yield. 

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