Ten crown ethers with pendant carboxylic acid groups are synthesized from corresponding hydroxy crown ethers. Within this series of crown ether carboxylic acids there is systematic variation of the following: (a) the crown ether cavity size, while holding the pendant carboxylic acid group constant, (b) the length of the linkage which joins the carboxylic acid group to a common polyether ring, and (c) the lipophilicity, while keeping the polyether ring and linkage which joins the carboxylic acid and polyether ring portions invariant. Dissociation constants of the crown ether carboxylic acids in water are determined.
A new type of llpophlllc crown ether carboxylic acld, symbls[4(5)-tert-butylbenro]-l6-crown-5-oxyacetlc acid (6) Is prepared and compared with P-(sym-dibenzo-16-crown-5oxy)decanolc acid (5) In the competitive extraction and transport of elkall metal catlons from aqueous solutlons Into chloroform. Although the overall complexatlon behavlor of 5 and 6 for alkall metal cations In solvent extractlon and In llquld membrane transport Is qulte slmllar, 6 exhlblts complete excluslon of LI' and enhanced Na+/K+ selectlvity.
H2SO4 which was carefully added until vigorous reaction stopped. The EtjO layer was separated, and the aqueous layer was extracted with EtjO three times. The combined ether solution was washed with water and saturated NaCI solution and dried over anhydrous MgS04. Distillation at 85-90 °C (12 mmHg) gave 49.4 g (85% yield) of 5a, a colorless liquid. The product was identical with an authentic sample prepared by another method.3 (c/s-6-Methyltetrahydropyran-2-yl)ethyl Acetate (5b).Acetyl chloride (10.9 g, 0.139 mol) was added slowly to 5a (20 g 0.139 mole) and dry pyridine (11.0 g, 0.139 mol) in an ice bath. The mixture was allowed to stand overnight, and then 100 mL of ice-water was poured into the flask. The organic layer was separated, and the aqueous layer was extracted three times with Et^O. The combined Et^O solution was washed with water and saturated NaCI solution and dried over anhydrous MgS04.Distillation at 103-106 °C (12 mmHg) gave 23.01 g (89%) of a colorless liquid, 5b: IR (NaCI disk 2930 (
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