Analytical Sciences

Determination of the Standard Entropy Changes of Ion Transfer for 1-Alkylpyridinium Ions by Thermal Modulation Voltammetry with Laser Heating at a Water/1,2-Dichloroethane Interface

Riho WATANABE, Yui TERAUCHI, Makoto SAKAUE, and Teruo HINOUE

Department of Chemistry, Faculty of Science, Shinshu University, Matsumoto, Nagano 390-8621, Japan

When laser light impinges upon a liquid–liquid interface between an optically transparent aqueous and opaque organic phase from the aqueous to organic phase, the temperature at the interface and the interfacial region rises. Using this rise in temperature, we have proposed and developed thermal modulation voltammetry at an interface between two immiscible electrolyte solutions (TMV-ITIES) and have determined the standard entropy changes of ion transfer, ΔS_tr^°,O→W. In this work, we have determined ΔS_tr^°,O→W for four 1-alkylpridinium ions, namely 1-methylpyridinium ion (MePy⁺), 1-ethylpyridinium ion (EtPy⁺), 1-propylpyridinium ion (PrPy⁺), and 1-buthylpyridinium ion (BuPy⁺) by TMV-ITIES. As a result, we obtained the ΔS_tr^°,O→W values of 108.0 ± 0.5 (n = 3), 75.8 ± 4.4, 55.6 ± 1.2, and 42.7 ± 0.9 J K⁻¹ mol⁻¹ for MePy⁺, EtPy⁺, PrPy⁺, and BuPy⁺, respectively. From these values of ΔS_tr^°,O→W, we have suggested that MePy⁺, EtPy⁺, and PrPy⁺ are classified as water structure-breaking ions and BuPy⁺ as a weak water structure-making ion. Further, we discuss the relationship between the standard free energy change, ΔG_tr^°,O→W, and ΔS_tr^°,O→W of ion transfer for 1-alkylpridinium ions and tetraalkylammonium ions.

J-STAGE: View this article in J-STAGE