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【讨论】甲醇除水。。 已有4人参与
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| 甲醇作为溶剂套用 对水分要求很严格 （0.1%以下），几次套用下来 水分达1% 不知道有什么好方法 不考虑上塔 氧化钙都用过 效果貌似不是很好 不知道都有哪些好方法 |
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试剂纯化手册上的方法 Methanol [67-56-1] M 32.0, b 64.5°, d15 0.79609, d25 1.32663, n15 1.33057, n25 1.32663, pK25 15.5. Almost all methanol is now obtained synthetically. Likely impurities are water, acetone, formaldehyde, ethanol, methyl formate and traces of dimethyl ether, methylal, methyl acetate, acetaldehyde, carbon dioxide and ammonia. Most of the water (down to about 0.01%) can be removed by fractional distn. Drying with CaO is unnecessary and wasteful. Anhydrous methanol can be obtained from "absolute" material by passage through Linde type 4A molecular sieves, or by drying with CaH2, CaSC>4, or with just a little more sodium than required to react with the water present; in all cases the methanol is then distd. Two treatments with sodium reduces the water content to about 5 x 10~5%. [Friedman, Gill and Doty J Am Chem Soc 83 4050 1961.] Lund and Bjerrum [Chem Ber 64 210 7937] warmed clean dry magnesium turnings (5g) and iodine (0.5g) with 50-75mL of "absolute" methanol in a flask until the iodine disappeared and all the magnesium was converted to methoxide. Up to IL of methanol was added and, after refluxing for 2-3h, it was distd off, excluding moisture from the system. Redistn from tribromobenzoic acid removes basic impurities and traces of magnesium oxides, and leaves conductivity-quality material. The method of Hartley and Raikes [/ Chem Soc 127 524 7925] gives a slightly better product. This consists of an initial fractional distn, followed by distn from aluminium methoxide, and then ammonia and other volatile impurities are removed by refluxing for 6h with freshly dehydrated CuSO4 (2g/L) while dry air is passed through: the methanol is finally distd. (The aluminium methoxide is prepared by warming with aluminium amalgam (3g/L) until all the aluminium has reacted. The amalgam is obtained by wanning pieces of sheet aluminium with a soln of HgCl2 in dry methanol). This treatment also removes aldehydes. |
5楼2010-06-27 16:17:49
