Pyrrolidine and Its Hydrates in the Solid State

Abstract

The crystals of new ambient pressure, high temperature (HT) polymorphs of neat pyrrolidine hemi- and hexahydrates were obtained using the IR laser assisted in situ crystallization method. They were subsequently investigated by single crystal X-ray diffraction and Raman spectroscopy. The transition from HT form to the known low temperature (LT) polymorph of the amine was monitored by X-ray powder diffraction. Although the investigated amine is an analogue to tetrahydrofuran (THF) which forms a stable clathrate hydrate, both binary pyrrolidine hydrates are dissimilar to the THF hydrate. The hexahydrate of pyrrolidine represents a class of semiclathrates where “guest” molecules are incorporated in the water framework. While cooling it undergoes a phase transition to the fully ordered phase. At higher temperatures the structure contains disordered pyrrolidine and water molecules. The latter adopts the same type of disorder as typical for H-disordered ice polymorphs (e.g., I h, I c, ...) and most clathrate hydrates.

Distortion of the Large Cages Encapsulating Cyclic Molecules and Empty Small Cages of Structure II Clathrate Hydrates

“…Figure c shows spherically distributed THP molecules with a full quasispherical symmetry. The distribution of THF and THP molecules obtained in this study are consistent with the crystal structure model obtained by the single-crystal X-ray structure analysis , and dynamics data of THF hydrate by quasielastic neutron scattering …”

“…Figure 4c shows spherically distributed THP molecules with a full quasispherical symmetry. The distribution of THF and THP molecules obtained in this study are consistent with the crystal structure model obtained by the single-crystal X-ray structure analysis 44,67 and dynamics data of THF hydrate by quasielastic neutron scattering. 68 It is also known that the smaller C 3 H 8 and iso-C 4 H 10 molecules have a spherical distribution in the 5 12 6 4 cages of the sII hydrate, 33,50,51 whereas CO 2 and C 2 H 6 in 5 12 6 2 cages of sI hydrate are distributed near the equatorial plane of the cage, with the long axis of these guests lying in the plane.…”

Molecular Aggregation in Binary Mixtures of Pyrrolidine, N-Methylpyrrolidine, Piperidine, and N-Methylpiperidine with Water: Thermodynamic, SANS, and Theoretical Studies

“…In crystalline hydrates of pyrrolidine, however, N−H•••O bonds occur beside the stronger O−H•••N bonds. 21 The former may be present in the liquid solutions in methanol, the more so because there is just one hydrogen atom in methanol molecule capable of forming O−H•••X bonds, while two such atoms are in that of water. Thus, the positive enthalpy of the N−H•••N bonds breaking upon solution would be compensated by the negative effect of the N−H•••O bonds formation.…”

“…15 Recently, crystal structures of pyrrolidine hemi-and hexahydrates were reported. 21 In the former, two amine molecules are hydrogen-bonded with one water molecule. The solid hexahydrate is a semiclathrate structure with guest amine molecules participating in the hydrogenbonded network of the host water.…”

Separation of alcohol isomers by host-guest chemistry

“…In the structure the amine molecules are incorporated to this network thus the hexahydrate is example of semiclathrate [2]. This structure is isostructural with hexahydrate of pyrrolidine [3] saturated analogue of 3pyrroline. Contrary to the pyrrolidine hexahydrate however, corresponding structure with 3-pyrroline does not undergo order-disorder phase transition.…”