Kinetics of complexation of macrocyclic polyethers with alkali metal ions. I. Sodium-23 nuclear magnetic resonance of sodium dibenzo-18-crown-6 in N,N-dimethylformamide
Kinetics of complexation of macrocyclic polyethers with alkali metal ions. I. Sodium-23 nuclear magnetic resonance of sodium dibenzo-18-crown-6 in N,N-dimethylformamide
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大环聚醚与碱金属离子的络合动力学。
DOI：
10.1021/ja00755a002
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发表时间：
1971
影响因子：
15
通讯作者：
M. Shporer
中科院分区：
文献类型：
--
作者：
E. Shchori;J. Jagur;Z. Luz;M. Shporer
报道了使用 23Na 核磁共振光谱法对钠离子与二苯并-18-冠-6 (DEC) 在 DMF 中的络合反应进行了动力学研究。溶剂化钠和 DEC 络合物中 23Na 的化学位移非常接近，但由于络合物中钠周围缺乏立方对称性，快速四极弛豫导致该物质的线宽比溶剂化钠宽得多（约 25 倍）。在含有这两种物质的溶液中，两者之间存在钠交换。在30℃到0℃的温度范围内，这种交换速率与23Na核的弛豫速率相当，从而影响核磁共振谱线形状。对线形状的定量分析得出了两种物质中钠的平均寿命值。在含有0.3-1.9 M NaSCN和0.1-0.2 M DEC的溶液中在60至+80的温度范围内进行测量。通过使用LiSCN调节离子强度。在一些运行中，BPhr 被用作抗衡阴离子而不是 SCN-。对结果的浓度依赖性分析表明，主要的交换机制涉及络合平衡 Na++ DEC<= í Na+, DEC。解络反应的伪一级速率常数为 25，外推至零离子强度，活化能分别为~ 101 2345 6sec-1 和 12.6±0.6 kcal/mol。络合反应的平衡常数通过电导测定确定在0和40之间。发现在 25 时为～～ 600 M-1，AH=～6 kcal/mol 和 AS=～7 eu。根据这些结果，估计 250 时络合反应的速率常数为 6 X 107 8M-1 sec-1，活化能为 6.5 kcal/mol。
A kinetic study of the complexation reaction of sodium ions with dibenzo-18-crown-6 (DEC) in DMF, using 23Na nmr spectroscopy, is reported. The chemical shifts of 23Na in the solvated sodium and in the DEC com-plex are very nearly the same, but due to the lack of cubic symmetry around sodiumin the complex, fast quadrupole relaxation causes the line width in this species to be much broader (about 25 times) than in solvated sodium. In solutions containing both species, there is sodium exchange between the two. In the temperature range between—30 and 0, the rate of this exchange is of the order of the relaxation rate of the 23Na nuclei, thus affecting the nmr line shape. A quantitative analysis of the line shape yields values for the mean lifetimes of sodium in the two species. Measurements were performed in solutions containing 0.3—1.9 M NaSCN and 0.1-0.2 M DEC in the temperature range—60 to+ 80. The ionic strength was adjusted by using LiSCN. In some runs BPhr was used as a counteranion instead of SCN-. Analysis of the concentration dependence of the results indicates that the dominant exchange mechanism involves the complexation equilibrium Na++ DEC<= í Na+, DEC. The pseudo-first-order rate constant for the decomplexation reaction at 25, extrapolated to zero ionic strength, and the ac-tivation energy are found to be~ 101 2345 6sec-1 and 12.6±0.6 kcal/mol, respectively. The equilibrium constant for the complexation reaction was determined conductometrically between 0 and40. It is found to be-~ 600 M-1 at 25 with AH=—6 kcal/mol and AS=—7 eu. From these results, the rate constant of the complexation re-action at 250 is estimated to be 6 X 107 8M-1 sec-1, with an activation energy of 6.5 kcal/mol.