Abstract:The hydrophilicity of surface-active crown compounds and their change upon the addition of electrolytes were investigated by measuring the phase-inversion temperature (PIT), the phenol index, and the cloud point. Sodium chloride and potassium chloride were observed to raise the hydrophilicity of 15-crowns and 18-crowns respectively, in contrast with their lowering effect on the hydrophilicity of usual poly(oxyethylene)-type nonionics. The effective HLBs of dodecyl crown ethers, estimated from both the PIT and … Show more
Lipophilic crown ethers are useful for metal ion extraction: they are soluble in organic phases and insoluble in aqueous ones. The lipophilicity can be enhanced by long‐chain hydrocarbon residues, by expanding the carbon content in the crown skeleton and by other structural variations.
The complexation behaviour and, therefore, the selectivity of crowns in extraction processes can be altered by changing the crown diameter, the kind and the number of hetero atoms within the crown ring or at positions outside the cycle. Furthermore, for the electro‐neutrality of the extracted species it is necessary to transfer also an anion into the organic phase. This problem can be solved with crown ether acids or with other hydrophobic inorganic or organic anions.
In this review with 276 references many synthetic routes and examples of such lipophilic crown ethers are described. Special attention is given to the building blocks for the crown ethers, which are important in the extraction area. So the survey should open a view for similar syntheses of new metal extraction reagents with coronand structure.
Lipophilic crown ethers are useful for metal ion extraction: they are soluble in organic phases and insoluble in aqueous ones. The lipophilicity can be enhanced by long‐chain hydrocarbon residues, by expanding the carbon content in the crown skeleton and by other structural variations.
The complexation behaviour and, therefore, the selectivity of crowns in extraction processes can be altered by changing the crown diameter, the kind and the number of hetero atoms within the crown ring or at positions outside the cycle. Furthermore, for the electro‐neutrality of the extracted species it is necessary to transfer also an anion into the organic phase. This problem can be solved with crown ether acids or with other hydrophobic inorganic or organic anions.
In this review with 276 references many synthetic routes and examples of such lipophilic crown ethers are described. Special attention is given to the building blocks for the crown ethers, which are important in the extraction area. So the survey should open a view for similar syntheses of new metal extraction reagents with coronand structure.
A series of N‐alkyl dihydroxy monoazacrown ethers (1) was synthesized, and their surface properties were investigated compared to those of N‐alkyl monoazacrown ethers (2) and open chain oxyethylenated long chain alkylamines (3). The complexation ability of1 toward alkali metal cations, a distinguished characteristic of crown compounds, was deduced to work even in the aqeuous solution from the values of MJX-TeXAtom-ORDnormalΔfalse~TCP, although it is weaker than typical monoazacrown ethers (2). The presence of two hydroxyl groups contributes to the large increase in hydrophilicity of monoazacrown ring and to the large surface excess of the surfactant molecule (1). A small occupation area to the solution surface is noted as a characteristic feature of the title coumpound (1).
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