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结构相似,性质相近的混合物的分离,是科研中经常遇到而又难于解决的问题。例如:从炔雌醇(1)出发所获得的4-羟基炔雌醇3-甲醚(Ⅲ),与中间产物4-氨基炔雌醇3-甲醚(Ⅱ)的结构相似,它们的唯一差别在于4-位上一个是氨基,另一个则是羟基。这两个基团极性相差很小,因而两个化合物的极性相近。薄层谱显示出(Ⅱ)与(Ⅲ)的Rf值仅相差0.05,是难分离的混合物。用一般柱层析法不能把它们分开。因此探索难分离混合物的分离具有很大的实际意义。
The separation of mixtures with similar structures and similar properties is a problem often encountered in scientific research but difficult to solve. For example, the 4-hydroxyethynylestradiol 3-methyl ether (III) obtained from ethinylestradiol (1) has a similar structure as the intermediate 4-aminoethylestradiol 3-methyl ether The difference is that one of the 4-position is an amino group, the other is a hydroxyl group. The polarities of these two groups differ so little that the polarities of the two compounds are similar. The TLC shows that the Rf values of (II) and (III) differ only by 0.05, making it a poorly separable mixture. They can not be separated by general column chromatography. Therefore, it is of great practical significance to explore the separation of hard-to-separate mixtures.