Kinetics and equilibria of cryptate formation in propylene carbonate

Abstract

Stability constants and dissociation rates of alkali metal cryptates have been measured in propylene carbonate, and the corresponding formation rates obtained from a combination of the two. Qualitatively, the variation in stability constants with cation size and ligand is similar to that in water, but the complexes are up to 107 times more stable in propylene carbonate. It is shown that for a given ligand the free energy transfer of the cryptates from water to propylene carbonate varies systematically with the cation enclosed and tends to be at a minimum for the most stable cryptate. The higher stability constants in propylene carbonate relative to water are a result of both smaller dissociation rates and, to a lesser extent, larger formation rates. Within propylene carbonate, the cryptand selectivity is reflected almost entirely in the dissociation rates. The dissociation rates are much more susceptible to acid catalysis in propylene carbonate than in water.

Crystal environments and geometries of leucine, isoleucine, valine and phenylalanine provide estimates of minimum nonbonded contact and preferred van der Waals interaction distances

“…There are a number of effects common to most crystal structure determinations which may introduce systematic errors. In this analysis there is a shrinkage of the average bond lengths involving atoms which have a large (10) Momany, F. A.; Carruthers, L. M.; McGuire, R. F.; Scheraga, FI. A. J. Phys.…”

Solvent dependence of the stability of cryptate complexes

“…Results of kinetic and thermodynamic studies in propylene carbonate (PC) have already been reported. 3 A considerable amount of thermodynamic data on ion-solvent interactions in these solvents exists. 4 The results are analyzed according to the solvent dependence of the free energies of the various species M"+, L (=Cry), and ML""1" (=MCry"+) in eq 3.…”

Kinetic hydrogen isotope effects for proton transfer between carboxylic acids and the monoprotonated crysptand (2,1,1)H+ in methanol

“…(ii) Protonation of(2,1,1)D + in CH30D.-The experimental techniques, ranges of concentration, and methods of analysis of the data are the same as those described above for measure- kDDA "1 ments in MeOH. The only difficulty was in deciding upon the value of the equilibrium constant, K, to be used in equation (12), as pK, values were not available in MeOD. Based on studies of weak acids in H 2 0 and D 2 0 l9l2O which show that for acids of similar strength ApK ( H 2 0 -D 2 0 ) is almost constant [e.g.…”

“…Initial concentration of [(2,1,1)H]A. Equilibrium concentrations calculated using K = 2.0 x from equation(12) with kHA = 1.41 x lo3 mol-' dm3 s-I and K = 2.0 x…”