Thiocrown ethers

A new type of approach to thiocrown ether synthesis involving a [2 + 2] coupling of a>-dithiol and w-dihalide units in the presence of a boron aluminium alkoxide couple has been described [27]. 

As a conclusion, we note that macrocyclic compounds (thiocrown-ethers) are described as belonging to the group of S,O-donors [262,567,939,940]. Also, a number of polyheterodonor ligand systems are known, for example, thiobenzoylhydrazones, containing N,0,S-donor atoms [941]. 

The acid-catalyzed condensation of 2,2 -thiodiethanethiol with carbonyl compounds under properly chosen conditions leads in good yield to thiocrown ethers containing thioacetal units. The reaction with benzaldehyde has been examined in detail, and the monomer 129, dimer 130, and polymer products have been characterized. The reaction was driven in good yield to any of these products by a proper choice of conditions (Equation 20 <1994J(P1)707>). 

The synthesis of thiocrown ether clathrochelates can be implemented both by a direct template reaction on an appropriate metal ion (for instance, in the presence of Cd ions) and by a stepwise procedure, as shown in Scheme 131. 

Thiocrown ethers are also used for extraction separation of metal ions [52-57]. The cationic complexes formed by these ethers with Cu(I), Ag, Pd(II), Pt(II) are extractable from acidic media (e.g., by 1,2-dichloroethane) in the presence of, e.g., picric acid. 

References concerning research studies of enyzme-like polymers conducted during the period of 1978-1982, catalytic properties of water-soluble imidazole-containing polymers during ester hydrolysis, as well as the latest achievements in the manufacture and application of high-molecular weight catalysts containing thiocrown-ethers or crown-sulfides, can be found in previous reviews [199-201]. 

It has been found that acid-catalyzed condensation of 2,2 -thiodiethanethiol [3570-55-6] (102) with carbonyl compounds (or equivalents thereof) carried out in solution can, imder chosen conditions, lead to good yields to thiocrown ethers containing thioacetal units (262). A detailed examination of a prototype reaction of (102) with benzaldehyde [100-52-7] (103) showed that depending on the reaction conditions, a different distribution of the products [monomer (104), dimer (105), and polymer (106) of M = 11,250 with polydispersity = 1.9] is achieved. Products (104), (105), and (106) with maximum yields 87, 62, and 99% respectively, can be obtained. 

Distal bridging of calixarenes has also been performed on resorcinarenes. An interesting example is the thiocrown resorcinarenes synthesised by Konishi et al. by the bridging of distal dibromoresorcinarene with 2-mercaptoethyl ether, propane-1,3-dithiol, and ethane-1,2-dithiol (Scheme 10.15) [33]. The octahydroxythiacrown... 

Solvent extraction of Ag(I), Hg(II), Cu(II) and Cd(II) from nitrate aqueous solutions with copolymers 6 was studied. Poly(14-thiacrown-4) and poly(20-thiacrown-6) copolymers were selective for Au(I) since, as soft acids, they have a high affinity for thiacrown ethers, as soft bases. On the other hand, 2-aminomethyl-17-thiocrown-5 on a polystyrene support, was found to be selective for Hg(II) [6]. In competitive studies of metal cations, mercury(II) was... 

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