Synthesis of Mono-, Bis-, and Tris-dithiapentaoxacrown Ethers: Complexation Studies with Some Metal Picrates

Abstract

Dithiatetraoxa-1a, dithiapentaoxa-1b, dithiahexaoxa-1c, bis-dithiapentaoxa-18, and tris-dithia-pentaoxa-crown ethers 22 were synthesized in order to study the complexation of bis-and tristhiacrown ethers in which the cycles are bounded to the same carbon atom, with metal picrates. Measurements of the affinity of meial ions (Cs⁺, Rb⁺, Ba²⁺, K⁺, Ag⁺, Pb²⁺, Sr²⁺, Ca²⁺, Cu²⁺, Mg²⁺), to these molecules represented by extractability, defined by equation 1, showed that Ag⁺ was strongly attracted by 1a (95%), 1b (94%), 1c (65%), 18 (193%), and 22 (270%). It appeared that the extractability increased linearly with the number of cavities in the molecule (cf. Mono-1b, bis-18, and tris-crown ethers 22). However, extractabilities of Pb²⁺ shown by only 21-membered 1b, 18, and 22, in spite of much lower values than those of Ag⁺, were not additive, For noncompetitive transport of metal ions (Ba²⁺, Ag⁺, Pb²⁺) through a liquid membrane, 1a favored transport of Ag⁺ over Pb²⁺. However 1b-c favored transport of Pb²⁺. The tendency of the former may be responsible for negligible extractability of Pb²⁺ due to the size of the cavity, whereas the latter may be attributable to a weaker affinity for Pb²⁺ than for Ag⁺ so that Pb²⁺ associated weakly with 1b-c is transported readily. For competitive transport of metal ions (Ba²⁺, Ag²⁺,Pb²⁺,Cu²⁺) by dithiacrown ethers 1a-b, and 22, only transport of Pb²⁺ occurred predominantly. The degree of complexation obtained based on the comparison of ¹H NMR spectra of 1a-c, 18, 22 and the corresponding Ag⁺ complexes was almost the same as those obtained from the solvent extraction.

Key Words:

• Dithiapentaoxacrown ethers
• metal picrates
• extractability
• liquid membrane
• jobs plot