Thermodynamic Study on Transfer from Water to Polar Nonaqueous Solvents of 18-Crown-6 and Its 1:1 Complexes with Alkali Metal Ions
Thermodynamic Study on Transfer from Water to Polar Nonaqueous Solvents of 18-Crown-6 and Its 1:1 Complexes with Alkali Metal Ions
复制标题
18-Crown-6及其与碱金属离子1:1配合物从水转移到极性非水溶剂的热力学研究
DOI：
10.2116/analsci.16.929
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发表时间：
2000
影响因子：
1.6
通讯作者：
S. Katsuta
中科院分区：
文献类型：
--
作者：
Y. Takeda;M. Kanazawa;S. Katsuta
用溶剂萃取法精确测定了18-冠-6（18 C6）从水到各种极性非水溶剂的转移吉布斯自由能（Δ G ° tr）、焓（Δ H ° tr）和熵变（Δ S ° tr）。利用这些数据，结合已知的碱金属离子（M^+）在水和非水溶剂中的迁移热力学量和络合热力学量，我们从Ph_4As^+/Ph_4B^-假设出发，通过热力学循环计算了M（18 C6）^+络合物从水到溶剂的迁移热力学参数。M（18 C6）^+配合物的Δ H °_tr和Δ S °_tr值随溶剂和碱金属离子的变化而变化，18 C6配合物的Δ H °_tr和Δ S °_tr值也随溶剂的变化而变化。Δ H °_tr和Δ S °_tr均为正值且较大，反映了18 C6与水之间的强氢键作用。在给定的溶剂中，18 C6与Rb^+和Cs^+形成的络合物比与Na^+和K^+形成的络合物更稳定。这表明，配合物中的Na^+和K^+被18 C6屏蔽，与Rb^+和Cs^+相比，更有效地屏蔽了周围的溶剂。在所有的M（18 C6）^+配合物中，只有Na（18 C6）^+从水到DMF的Δ H °_tr值为正。从这一结果和其他结果可以得出结论，Na（18 C6）^+络合物比其他络合物经历更强烈的疏水水合作用。
The Gibbs free energy (Δ G °_tr), enthalpy (Δ H °_tr), and entropy changes (Δ S °_tr) for transfer of 18-crown-6 (18C6) from water to various polar nonaqueous solvents were precisely determined by solvent extraction. By using these data, and the known values of thermodynamic quantities for transfer of alkali metal ions (M^+) and those for complexation in water and the nonaqueous solvents, we calculated the thermodynamic parameters of transfer of the M(18C6)^+ complexes from water to the solvents from the Ph_4As^+/Ph_4B^- assumption via a thermodynamic cycle. The Δ H °_tr and Δ S °_tr values of the M(18C6)^+ complexes vary considerably with the solvent and with the alkali metal ion, and also those of 18C6 do with the solvent. The values of Δ H °_tr and Δ S °_tr are all positive and large, reflecting strong hydrogen bonding between 18C6 and water. 18C6 complexes with Rb^+ and Cs^+ are enthalpically more stable in a given solvent than those with Na^+ and K^+. This shows that Na^+ and K^+ in the complexes are more effectively shielded by 18C6 from surrounding solvents than Rb^+ and Cs^+. Among all the M(18C6)^+ complexes, positive Δ H °_tr value from water to DMF is found only for Na(18C6)^+. It is concluded from this and the other results that the Na(18C6)^+ complex undergoes hydrophobic hydration more strongly than the other complexes do.