Thermodynamic Studies of Aqueous Solutions of 2,2,2-Cryptand at 298.15 K: Enthalpy鈥揈ntropy Compensation, Partial Entropies, and Complexation with K+ Ions

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• 作者：Vasim R. Shaikh ; Santosh S. Terdale ; Abdul Ahamad ; Gaurav R. Gupta ; Dilip H. Dagade ; Dilip G. Hundiwale ; Kesharsingh J. Patil
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：December 19, 2013
• 年：2013
• 卷：117
• 期：50
• 页码：16249-16259
• 全文大小：420K
• 年卷期：v.117,no.50(December 19, 2013)
• ISSN：1520-5207

文摘

The osmotic coefficient measurements for binary aqueous solutions of 2,2,2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8] hexacosane) in the concentration range of 0.009 to 0.24 mol路kg^鈥? and in ternary aqueous solutions containing a fixed concentration of 2,2,2-cryptand of 0.1 mol路kg^鈥? with varying concentration of KBr (0.06 to 0.16 mol路kg^鈥?) have been reported at 298.15 K. The diamine gets hydrolyzed in aqueous solutions and needs proper approach to obtain meaningful thermodynamic properties. The measured osmotic coefficient values are corrected for hydrolysis and are used to determine the solvent activity and mean ionic activity coefficients of solute as a function of concentration. Strong ion-pair formation is observed, and the ion-pair dissociation constant for the species [CrptH]⁺[OH^{鈥?/sup>] is reported. The excess and mixing thermodynamic properties (Gibbs free energy, enthalpy, and entropy changes) have been obtained using the activity data from this study and the heat data reported in the literature. Further, the data are utilized to compute the partial molal entropies of solvent and solute at finite as well as infinite dilution of 2,2,2-cryptand in water. The concentration dependent non-linear enthalpy鈥揺ntropy compensation effect has been observed for the studied system, and the compensation temperature along with entropic parameter are reported. Using solute activity coefficient data in ternary solutions, the transfer Gibbs free energies for transfer of the cryptand from water to aqueous KBr as well as transfer of KBr from water to aqueous cryptand were obtained and utilized to obtain the salting constant (k_s) and thermodynamic equilibrium constant (log鈥?i>K) values for the complex (2,2,2-cryptand:K+) at 298.15 K. The value of log鈥?i>K = 5.8 卤 0.1 obtained in this work is found to be in good agreement with that reported by Lehn and Sauvage. The standard molar entropy for complexation is also estimated for the 2,2,2-cryptand鈥揔Br complex in aqueous medium.}