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Thermodynamic Studies On The Complexing and Extraction of Cations by Neutral Macrocyclic Complexing Agents.

Ling, How Chiong. (1981) Thermodynamic Studies On The Complexing and Extraction of Cations by Neutral Macrocyclic Complexing Agents. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

The general chemistry of neutral macrocyclic ligands is reviewed, and a rather exhaustive survey is reported of the thermodynamic parameters for the complexing of univalent cations with crown ethers (18-crown-6, dibenzo-18-crown-6) and cryptands. The extraction of cations (M+) by a neutral ligand (L) is discussed in terms of the thermodynamic cycle (B = G, H or S), where the subscript 'o' denotes a species in the organic phase: Values of Gt(18C6) and Gt(222) have been obtained by distribution experiments between water and n-tetradecane and the required solvent and n-tetradecane, and values of AHt(18C6) by direct solution calorimetry. A number of values of G(M+) and H(M+) have also been determined: these include transfer from water to methanol/water (70/30 wt. %) and wet tri-n-butyl-phosphate (TBP). The thermodynamic parameters for complexing of 18-crown-6 (and also dibenzo-18-crown-6) with a number of univalent cations in methanol have been obtained by a novel procedure based on simple batch solution calorimetry; similar experiments are reported using wet TBP. In this way, using parameters obtained in this work and data from the literature, the cycle (above) was constructed for systems involving univalent cations, the ligands 18C6 and cryptand 222, and solvents methanol/water (70/30 wt. %), methanol, dimethylsulphoxide, N,N-dimethylformamide, propylene carbonate and acetonitrile. It is shown that the water/methanol transfer using cryptand 222 is the most selective with respect to K+ and Na+ and generally is also the most selective. Distribution experiments on sodium and potassium picrate between water and TBP both in the absence and presence of 18-crown-6 have been carried out and analysed by equations that take into account activity coefficients of the ionic species in each phase, to yield values of Gt(M++ Pic-), Gt(M+Pic-), Gt(M+L + Pic-) and Gt(M+LPic-). Calorimetrically determined values of Ht(M+ + Pic-) and H(M+L + Pic-) have also been obtained. The true extraction of ions by 18-crown-6 in TBP has been compared with hypothetical extraction into water-miscible solvents, and conclusions are drawn as to the requirements for a system capable of selectively extracting cations.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Ling, How Chiong.
Date : 1981
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1981.
Depositing User : EPrints Services
Date Deposited : 06 May 2020 12:15
Last Modified : 06 May 2020 12:20
URI: http://epubs.surrey.ac.uk/id/eprint/855837

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