Competitive Intercalation Research Articles

Efficient separation of pyridinedicarboxylates by preferential anion exchange intercalation in [LiAl2(OH)6]Cl·H2O

All six isomers of pyridinedicarboxylate (2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA) can be intercalated by the layered double hydroxide [LiAl2(OH)6]Cl·H2O in water at 100 °C to give the fully ion-exchanged first stage intercalation compounds [LiAl2(OH)6]G0.5·xH2O (G = 2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA; x = 2–3.5) . The observed interlayer separations for the intercalates vary from 10.9 A for the high temperature form of [LiAl2(OH)6](3,5-PDA)0.5·2H2O to 14.8 A for [LiAl2(OH)6](2,3-PDA)0.5·3H2O. When a solution containing an equal concentration of two or more of the pyridinedicarboxylate anions is added to a suspension of [LiAl2(OH)6]Cl·H2O in water then the host exhibits preferential anion-exchange intercalation. Following an extensive series of competitive intercalation reactions involving two component through to six component mixtures we were able to determine the preference order for intercalation of all six PDA guests in [LiAl2(OH)6]Cl·H2O. The order was found to be 2,5-PDA > 2,3-PDA > 2,4-PDA > 2,6-PDA ≈ 3,5-PDA ≈ 3,4-PDA in water at 100 °C.

Synthesis and characterization of pillared clays containing both Si and Al pillars

A Wyoming montmorillonite clay has been intercalated using the competitive ion exchange of aluminum hydroxy polycations and oligosilsesquioxanes. Whereas the intercalation of montmorillonite by the products of hydrolysis of trichlorosilylethylpyridine yields an heterogeneous solid, with a large fraction non-intercalated, the X-ray diffraction shows that competitive intercalation permits a nearly complete intercalation of the material. The lattice spacing of 21.4 Å after ion exchange, is determined by the size of the largest oligosilsesquioxane cations. It is reduced to 17.4 Å after calcination at 873 K where 29Si and 27Al MAS-NMR show the existence of the two types of pillars with respectively the siloxane and Al 13 structure. After calcination at 973 K, a clear 001 XRD line is observed, and the microporous volume is 0.13 ml g −1, thus showing a good thermal stability. The number and strength of acid sites determined by adsorption of ammonia is comparable to that of HY zeolites. This strong acidity is related in part to the stability of the structure, and to the retention of the individuality of the Al 13 pillars. The tetrahedral aluminum atom of the pillars is assumed to be responsible for this strong acidity.

Competitive intercalation and intercalary kinetics

Some features of the results of kinetic studies of the ion-exchanged bentonite (montmorillonite) catalysed reactions, i.e. alk-1-ene + aliphatic acid → ester trimethyl orthoformate + ketone → acetal + formate primary amine + primary amine → secondary amine + NH 3 are described and are interpreted as indicating that : (i) Long-chain alk-1-ene homologues are intercalated from solution with the same partition coefficient. (ii) Given that a reaction mechanism can be justified, it appears to be possible to evaluate partition coefficient ratios, and with some approximation, intercalary rate constants. (iii) In competitive intercalation of the mixed amines used in this study, it appears likely that the less basic component is preferentially intercalated. It is concluded that properly designed kinetic experiments can allow derivation of quantitative data regarding intercalation, and thus extend understanding of the nature of the process.