Journal of the Chemical Society. Perkin Transactions 2 (2001) p. 2505 - 2509 (1996)
Update date:2022-08-12
Topics:
Gobbi, Alessandro
Landini, Dario
Maia, Angelamaria
Penso, Michele
Cation electrophilic catalysis has been studied in nucleophilic substitution reactions of octyl methanesulfonate (1) promoted by complexes of macrocyclic polyethers 2-5 with alkali and alkaline-earth metal salts in chlorobenzene. The catalytic effect increases with increasing Lewis acid character of the cation, in the order Cs+ ～ Rb+ ～ K+ < Na+ < Li+ and Ba2+ < Sr2+ < Ca2+, and is mainly related to the ability of the polyether to shield the metal ion charge. Kinetic data clearly indicate that crown ethers 2-4 allow the metal ion participation in the activation process, whereas the cryptand [2.2.2,C10] (5), which more effectively binds the cation, inhibits catalysis. The lower reactivity of the complexes of alkaline-earth metal salts with both crown ethers and cryptands is most likely due to a higher interaction of the divalent cation with the anion in the ion-pair.
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