Proton cryptates. Kinetics and thermodynamics of protonation of the [1.1.1] macrobicyclic cryptand

摘要: The (1.1.1) macrobicyclic cryptand, binds one or two protons either outside inside its intramolecular cavity. structures of the different mono- and diprotonated forms thus produced have been assigned on basis their spectral properties proton transfer rates. Five identified, io/sup +/, o/sup +/o/sup +/i,i/sup i/sup +/i/sup thermodynamics kinetics interconversion studied. External diprotonation deuteration were studied in D/sub 2/O, acetone-d/sub 6/, methanol-d/sub 4/. protonation equilibrium with trifluoroacetic acid 6/ was slow enough at 270 K to yield separate /sup 1/H NMR signals for four sets nonequivalent externally monoprotonated species, (1).H/sup +/. In H/sub 2/O pK/sub al/ value species +/ is 7.1 +- 0.2, while a2/ approx. = 1. rates into out cavity are very slow. internally +/i, cannot be deprotonated unless cryptand destroyed. formation (i/sup +/i) +/) aremore » slow, activation energies about 110 kJ mol/sup -1/ each processes. rate first process varies pH. second internal removal as a function temperature. deprotonation depends hydroxide ion concentration also has an energy -1/. data provide means estimating thermodyanmic stability various protonated species. Cryptand thermodynamically strong kinetically extremely base. possible mechanisms discussed.« less