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碱金属离子的比色试剂是很少的。这主要是由于它们与普通的络合剂不能生成稳定的络合物。近年来发现冠醚与窝穴化合物可以与碱金属生成稳定的络合物,而且具有一定的选择性。可以设想,能否在这类化合物中引入生色基团,使其在络合时产生颜色变化。一个最简单的方案是在冠醚中引入一元弱酸的生色团。在络合时,质子离解而产生颜色变化。4′-间三硝苯基-氨基苯-15-冠醚
Alkali metal colorimetric reagents are rare. This is mainly due to their inability to form stable complexes with common complexing agents. In recent years, it has been found that crown ethers and cave compounds can form stable complexes with alkali metals and have certain selectivity. It is possible to imagine whether chromophore groups can be introduced into such compounds to give rise to a color change upon complexing. One of the simplest solutions is to introduce a monovalent weak acid chromophore into the crown ether. When complexed, the protons dissociate and produce a color change. 4’-m-trinitrophenyl-aminobenzene-15-crown ether