Template Effects. 2.¹ Convenient Syntheses of Crown Ethers Promoted by Ba⁺⁺ Ion in Aqueous Solution

References

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• Gokel , G. W. and Durst , H. D. 1976 . Synthesis , : 168
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• Ping-Lin , K. , Miki , M. and Okahara , M. 1978 . J.C.S. Chem. Comm. , : 504 A similar strategy has been recently applied by. These authors report the preparation of crown ethers in good yields by treatment of polyethyleneglycols with sulphonyl chlorides in the presence of alkali metal hydroxides in dioxan or glyme
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• Unpublished observation from this laboratory
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• Krespan , C. G. 1974 . J. Org. Chem. , 39 : 2351 The dibromides were obtained in about 50% yield from the corresponding glycols by treatment with PBr3 and pyridine, followed by hydrolysis and CC14 extraction, Further extraction of the mother liquors with CHC13 afforded the monobrominated materials, which may be used as well. Pentaethyleneglycol (bp 168–175 oC at 0.5 mm Hg) and exaethyleneglycol (bp 204–210 oC at 0.5 mm Hg) were obtained by fractional distillation of polyethyleneglycol 300 (Merck) on a 45-theoretical plates Todd Column. Eptaethyleneglycol was prepared from triethyleneglycol dichloride and diethyleneglycol according to The purity of the glycols was checked by vpc on a 1 m column, packed with SE30 on silanized chromosorb W 60–80
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• Pyrolysis was usually carried out by heating the crude materials up to 320 oC at 0.3 mm Hg. In the case of 18-crown-6 a higher temperature was required, 360 oC. In all cases the distillate contained significant amounts of hydroxylic materials, which could be removed by extraction with cold pentane, where they are practically insoluble
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• The identity of the crown ethers was checked by vpc (comparison with authentic samples) on a 1 m column packed with 0.4% FFAP plus 2% SE30 on silanized chromosorb W60–80
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• Dale , J. and Kristiansen , P. O. 1971 . J. C. S. Chem. Comm. , : 670 As determined by vpc9 as well as 1H-NMR analysis in the presence of the shift reagent Eu(DPM)3, according to. The two methods gave results consistent with each other
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