Liquid-liquid extraction of metal ions with several cyclic and acyclic tetrathio ethers was examined using picrate as the anion of the ion pair. Three new acyclic compounds were synthesized. Class b metal such as Ag(I ), Cu(I ), Pd(II) and Hg(II) were extracted well, whereas class a and class ab metals were not extracted at all except for Cu-(II) with each ligand, regardless of its being cyclic and acyclic tetrathio ethers. The extraction behavior of copper(l) was stoichiometrically examined. Copper(I) was extracted with five ligands(L) into 1,2-dichloroethane as ion pair compounds, [Cu(I )L]+Pic-. The extraction constant Kex for copper(I) with each ligand was determined. Copper-(I) is most effectively extracted with the tetrathio ether of the o-xylene derivative. It becomes clear that the configuration of ligands is reflected in the Kex value.Keywords Liquid-liquid extraction, class b metals, cyclic tetrathio ethers, acyclic tetrathio ethers Recently, the extraction behavior of metals with 1 ,4,8, 1 1-tetrathiacyclotetradecane (TTCT), which is one of the thiacrown compounds, into 1,2-dichloroethane using picrate as the counter anion has been examined.'-3 Consequently, it was clarified that class a and class ab metals, except for Cu(II), classified by Ahrland et al.4 were not extracted, while class b metals were extracted well. The detailed extraction behavior of class b metals such as Cu(I), Ag(I), Hg(II), Pd(II) and Cd(II) has been already reported.3 These studies made possible the extractive spectrophotometric determination of trace copper2 and silver with some thiacrown compounds.s-'Although the extraction of b metal ions with cyclic polythio ethers has been studied, that with acyclic polythio ethers has remained little studied.8'9 In the present study, acyclic polythio ethers corresponding to cyclic ones such as TTCT and Bz-TTCP, C3H6-(ETET)2 (3), o-, m-and p-xy-(ETET)2 (4), (5) and (6) as shown in Fig. 1 were synthesized. And the liquidliquid extraction of various metal ions was examined with these six ligands in order to compare the extraction behavior of acyclic tetrathio ethers with that of cyclic tetrathio ethers. The extraction behavior of copper(I) with the six tetrathio ethers was also examined in order to compare ligands with each other.
Experimental
ReagentsCyclic tetrathio ethers, TTCT (1) and Bz-TTCP (2) were synthesized by a method similar to that described by Rosen and Bush.10 Four acyclic tetrathio ethers which have two ethyl groups as terminal groups were synthesized by the method described below (Scheme 1).
2-MercaptodiethylsulfideIn a 500 ml three-necked flask, 2-ethylthioethanol (21.6 g, 0.2 mol), 44.2 ml of conc.hydrochloric acid and thiourea (15.25 g, 0.2 mol) were mixed and refluxed under nitrogen for 10 h. After cooling, 200 ml of 1 M Fig. 1 Ligands discussed in this work.