constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution
描述了(1H-
苯并咪唑-2-基-甲基)
膦酸H2(Bimp)+/-的合成:
2-氯甲基苯并咪唑与
氯甲酸乙酯反应生成1-碳乙氧基-
2-氯甲基苯并咪唑,并用亚
磷酸三甲酯处理用HBr
水溶液
水解后,得到H2(Bimp)+/-。在H2(Bimp)+/-中,一个质子位于N-3位,另一个质子位于
膦酸酯基团上;两种酸度常数都是通过电位pH滴定法(25℃; I = 0.1 M,NaNO3)在
水溶液中测定的,其pKa值分别为5.37 +/- 0.02和7.41 +/- 0.02。估计从H3(Bimp)+的P(O)(OH)2基团释放初级质子的酸度常数为:pKa = 1.5 +/- 0.2。此外,Bimp2-可以在其中性(N-1 / N-3)H位进一步质子化,得到
苯并咪唑酸酯残基,但是此反应仅在强碱性溶液(KOH)中发生;G. Yagil(J. Phys。Chem。,1967,71,1034)开发的H_标度的应用以及紫外分光光度法测量得出pKa