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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 11, Number 4
BKCSDE 11(4)
April 20, 1990 

 
Title
Conductance Study on the Characteristics of Solution Containing Crown Ethers and Univalent Cation Perchlorates
Author
Shim Sung Lee*, Sung Oh Park, Jong Hwa Jung, Bu Yong Lee, Si-Joong Kim
Keywords
Abstract
The equivalent conductance of univalent cation (potassium, silver, thallium and ammonium) perchlorates in methanol containing 18-membered crown ethers, 18-crown-6 (18C6) and 1,10-dithia-18-crown-6 (DT18C6) were measured at different temperatures. The equivalent conductances of ammonium perchlorate were increased by increasing content of DT18C6 exceptionally, due to more favorable solvations than complexations. From the equivalent conductance changes, the formation constants for 1:1 compmlexes have been determined, and the values of enthalpy and entropy changes have been calculated. The complexations of 18C6 and DT18C6 with the univalent cations under investigation are all exothermic and the ΔS values are all negative and no considerable differences around 50 J/ (k mol). The selectivity order of 18C6 is K+ > Tl+ > Ag+ > NH4+, while that of DT18C6 is Ag+ > Tl+ > NH4+ > K+. By sulfur substitutions in 18C6 result in significant decrease in stability, but the stability of Ag+-DT18C6 complex are 104 times larger than those of K+. This increase of stabilities for Ag+-DT18C6 complex are primary due to the result of favorable exothermic heat of reaction between the polarizable soft cation and soft sulfur centers. In NMR experiment, the stepwise additions of cation perchlorates into crown ether solutions induced two major spectral changes. First, the resonance all shift down field and the cation induced shifts were linear up to 1:1 cation/crown ratio, above which no further changes were observed. On the basis of these results, it could be concluded that 1:1 complex is formed. Second, the magnitudes of cation induced shifts were different each other in same ligand. By addition of silver ion to the solution of DT18C6, the largest shift of proton peak near the sulfur atom was observed. These effects are also arisen from the results of covalent bonding between "soft-soft" interactions.
Page
276 - 281
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