No abstract

The ring-enlarged crown ethers, 16-and 17-crown-5 and 19-to 22-crown-6, were synthesized and their cation-binding abilities were evaluated by solvent extraction of aqueous alkali metal picrates. The cation-binding abilities of less symmetrical crown ethers, 3a-e and 4a,b, were generally lower than those of the common symmetrical crown ethers 15-crown-5 (5a) and 18-crown-6 (5b), for which the less symmetrical arrangement of the donor oxygen atoms must be responsible. Compared with 18-crown-6 (5b), the ring-extended crown ethers, 3d, 3e, and 4b, showed a significant shift in cation selectivity, probably due to the enlarged cavity size. The thermodynamic parameters for the extraction of sodium and potassium picrates with 3a, 3c, and 5a,b were calculated from the change of the extraction equilibrium constants (Kex) between 10-25 °C. The stability of the cation-crown ether complexes was shown to be governed in general by the enthalpy change. However, a significant contribution of the entropy factor was found in unfavorable size combinations of K+ with 3a and Na+ with 3c.

Oligoethylene glycols and some related alcohols were efficiently tosylated with p-toluenesulfonyl chloride in a tetrahydrofuran–water (1:1) mixture in the presence of excess sodium hydroxide. This method is advantageous over the conventional tosylation in pyridine both regarding the work-up procedure, the yield, and the purity of the product, and may be potentially useful for the tosylation of certain acid-labile alcohols.

Thermodynamic parameters indicate that the enthalpy-ntropy compensation effect holds in general for complexation of cations with glymes/podands, crown ethers, cryptands, and macrocyclic antibiotics in various solvents. Thus the AH-TAS plots give fairly good linear relationships for each type of ligand, with different slopes (CC) and intercepts (TAS,) characteristic of the type. The nature of the cation-ligand interaction is discussed in terms of 01 and TAS, values.

Cyclodextrins (CDs), a series of cyclic oligomers of Dglucopyranose, are known to accommodate a variety of organic guests in their chiral hydrophobic cavities, forming inclusion compounds. Consequently, they have been applied widely to biomimetic chemistry as well as to separation science and technology, including chiral re~ognition.'-~ In sharp contrast to the well-documented stoichiometric and catalytic thermal asymmetric syntheses utilizing the CD's chiral c a v i t~, ' ,~,~-~* little effort appears to have been devoted to the study of asymmetric photochemistry in the chiral ~a v i t y ? , '~-'~ Only a few stoichiometric asymmetric photoreactions of CD complexes have hitherto been investigated in the solid state.I3-l5 We have reported recently that the direct irradiation at 185 nm of a 1:l complex of (a-cyclooctene (1Z) with p-CD in the solid state or in water suspension leads to prompt Z-E isomerization affording apparent photostationary-state (pss) En mixtures, but that the (@-isomer (1E) obtained is almost racemic: optical purity (op)