More-soluble Salts Research Articles

Facile resolution of racemic terbutaline and a study of molecular recognition through chiral supramolecules based on enantiodifferentiating self-assembly.

An effective resolving agent, (2S, 3S)-di-O-(p-toluoyl) tartaric acid(4), was screened using a 'family' approach to yield direct resolution of (R)-terbutaline (1) with high optical purity and yield. Molecular recognition was studied by X-ray crystallographic analyses of the single crystals of the pair of diastereomeric salts. The more-soluble salt formed a sheet supramolecular structure, and the less-soluble salt formed a columnar supramolecular structure by enantiodifferentiating self-assembly. The water molecule plays an important role during optical resolution, and makes the supramolecular structure of the less-soluble salt more thermodynamically stable than that of the more-soluble salt. Solvent system has little influence on the resolution.

Effect of a Substituent on an Aromatic Group in Diastereomeric Resolution

The diastereomeric resolution of p-substituted 1-arylethylamines by enantiopure (S)-3′,4′-methylenedioxymandelic acid ((S)-2) was carried out in order to know how an electron-donating or -withdrawing group on the aromatic group of the racemic amines would affect the efficiency of resolution. As a result, it was found that 1-arylethylamines having an electron-withdrawing substituent could be efficiently resolved by (S)-2, while the amines having an electron-donating group could not. The crystal structures of the less- and more-soluble salts, and the molecular orbital calculations of the ammonium cations indicated that the p-substituted electron-withdrawing group enhanced the positive charge on the meta-hydrogen of the aromatic group of the ammonium cations, which is favorable for the formation of a CH⋯π interaction in crystal.

Systematic study of chiral discrimination upon crystallisation. Part 2.1 Chiral discrimination of 2-arylalkanoic acids by (1R,2S )-2-amino-1,2-diphenylethanol

The resolution of 2-arylalkanoic acids by (1R,2S)-2-amino-1,2-diphenylethanol has been studied. It has been found that the position of a substituent on the aromatic group of the acids affects resolution efficiency to a considerable extent. Crystal structure analysis of the diastereomeric salts has revealed that a columnar hydrogen-bond network is commonly formed in the diastereomeric salts studied. A detailed analysis of the hydrogen-bond networks formed in the diastereomeric salts has enabled clear elucidation of the correlation between crystal structure and efficiency of resolution; differential stability of the crystals of less- and more-soluble salts, which results in large differences in solubility and subsequently in resolution efficiency, is found to arise from the inclusion of water molecules in the less-soluble salt, reinforcing the columnar hydrogen-bond network by strong hydrogen bonds, and from the absence of such water molecules in the more-soluble salt. On the other hand, when the resolution gave poor efficiency, such a remarkable difference in stability between the pairs of diastereomeric salts is not observed.

Chiral discrimination upon crystallisation of the diastereomeric salts of 1-arylethylamines with mandelic acid or p-methoxymandelic acid: interpretation of the resolution efficiencies on the basis of the crystal structures

The crystal structures of the diastereomeric salts of 1-arylethylamines with mandelic acid or p-methoxymandelic acid have been studied. This revealed that there was correlation between the efficiencies of the optical resolutions of the amines with the resolving reagents and the crystal structures of the salts. A characteristic hydrogen-bond layer, consisting of stable columnar structures and having a planar boundary surface, was found to be common to the less-soluble salt crystals; these crystals were considered to be stabilised from the viewpoint of both their hydrogen-bonding and van der Waals interactions. In contrast, in the corresponding more-soluble salts and in those diastereomeric salts which could not be separated by crystallisation, no such particularly stabilised crystal structure was formed; there only existed either columnar structures or planar boundary surfaces in these crystals. These results strongly suggest that for successful resolution it is necessary to realise a hydrogen-bond layer, consisting of stable columns and having planar boundary surfaces, in the crystals of one of the pair of diastereomeric salts. In order to achieve such a crystal structure, complementarily in molecular length between a target racemate and a resolving reagent must be considered the most important and fundamental factor.

The central palaeo-Andean basin of Bolivia (Potosi area) during the late Cretaceous and early Tertiary: reconstruction of ancient saline lakes using sedimentological, paleoecological and stable isotope records

In the Bolivian Eastern Cordillera, continental evaporites occur in late Cretaceous and early Tertiary Formations (Aroifilla, Chaunaca, uppermost El Molino, Santa-Lucia). Studies carried out in the Potosi basin show that these formations were deposited within an almost continuous lacustrine system subjected to large variations in hydrology independent of any significant marine contribution. Thus, in addition to tectonic effects, the hydrology was mainly governed by changes in the evaporation/precipitation ratio. Major evaporitic phases took place during arid periods which caused the contraction of the lakes and induced the formation of sub-perennial to ephemeral residual brine ponds trapped in the deep part of the lacustrine system (upper Aroifilla, middle Chaunaca, Santa-Lucia Formations). The crystallization of evaporitic minerals occurred as subaqueous precipitation in brine sheets and as interstitial growth both in the dry peripheral mud flats and in the central area when the water table fell below the sediment surface. Although the evaporite mineral assemblage only includes calcium sulfate, it is likely that moresoluble salts may have crystallized and subsequently underwent a partial or total dissolution. The source ions were the catchment basin rocks with a probable contribution of reduced sulfur compounds of volcanic origin. Wide variations of water redox conditions are substantiated by the isotopic composition of the sulfates. During wetter periods (Chaunaca p.p., El Molino), the expansion of the lacustrine system induced perennial conditions with slightly saline to freshwater although episodic desiccations may have occurred. The sedimentation is therefore characterized by decreasing evaporitic influences, carbonate sedimentation (shell coquinas, oolite/oncolite deposits, stromatolitic and thrombolitic build-ups, organic-rich laminated carbonates, etc) and, the diversification of the fauna and flora in the lake waters and near the shorelines. Toward the top of the El Molino Formation, episodic prevalence of sodic alkaline waters induced the formation of analcime-rich laminites. The rise of the lake level was responsible for the sporadic development of seaward outflows by which marine organisms may have entered into the lacustrine system. This late Cretaceous-early Tertiary continental domain was located in the subtropical belt where aridity and sub-desertic conditions alternated with more humid periods.

Structural Study of Optical Resolution. XI. The Crystal Structures of (+)589-Tris(biguanide)cobalt(III) Chloride d-Tartrate Trihydrate and Racemic Tris(biguanide)cobalt(III) Trichloride

Abstract The crystal structures of the more-soluble diastereomeric salt, (+)589-[Co(Hbg)3]Cl(d-tart)·3H2O (1), and the racemic chloride salt, [Co(Hbg)3]Cl3 (2), have been determined by X-ray analysis (R=0.033, 2788 reflections for 1 and R=0.056, 2785 reflections for 2), where Hbg=C2H7N5, d-tart=C4H4O62−. The more-soluble salt 1 is orthorhombic, with the space group P212121 Z=4, a=15.654(2), b=13.758(2), and c=11.010(1) Å. The racemic salt 2 is monoclinic, with the space group C2/c, Z=8, a=19.441(9), b=14.901(7), c=15.911(6) Å, and β=127.63(2)°. In 1, the complex cations and the Cl− ions are arranged alternately to form an infinite spiral chain, {Δ-[Co(Hbg)3]Cl}∞. Each d-tartrate is hydrogen-bonded to a twofold-screw-axis-related neighbor (–OH···OOC– 2.792 Å) to form an infinite chain, (d-tart)∞. In 2 two kinds of similar infinite spiral chains, {Δ-[Co(Hbg)3]Cl}∞ and {Λ-[Co(Hbg)3]Cl}∞, which are mirror images of each other are found. The structures of these two salts 1 and 2 are compared with those of the less-soluble diastereomeric chloride d-tartrate and the optically active chloride in both of which a similar infinite chain has been found, and the mechanism of chiral discrimination via the diastereomer formation is discussed.

The Crystal Structures of (+)589- and (−)589-trans(O)-Ethylenediaminebis(glycinato)cobalt(III) Hydrogen-d-tartrates and Their Thermal Behavior

Abstract The crystal structures of two diastereoisomeric salts, (+)589-trans(O)-[Co(gly)2en]H-d-tart·3H2O (1) and (−)589-trans(O)-[Co(gly)2en]H-d-tart·H2O (2), have been determined by three-dimensional X-ray analysis. The less-soluble salt (1) is monoclinic; space group, P21; Z=2, a=12.351(5), b=7.671(3), c=10.189(5) Å, and β=110.71(4)° (R=0.043, 2241 reflections). The more-soluble salt (2) is monoclinic; space group, P21; Z=2, a=11.135(4), b=10.037(3), c=7.716(3) Å, and β=98.61(3)° (R=0.064, 2076 reflections). A comparison of the (unit cell volume)/Z values of the two crystals shows that the crystal 1 is more tightly packed than the crystal 2. In both salts, adjacent complex cations form quite similar chain structures linked by (N–H…O) hydrogen bonds. The H-d-tart anions in 1 take a characteristic “head-to-tail” arrangement of an infinite chain of {H-d-tart}∞ along the b-axis. In contrast, this arrangement is not found in the more-soluble salt (2). From these findings, it can be considered that the discrimination of optical isomers in the H-d-tart system originates from the spiral chain structure of {H-d-tart}∞. The absolute configurations of (+)589- and (−)589-trans(O)-[Co(gly)2en]+ are determined to be Λ-δ and Λ-λ respectively. TG and DSC measurements were carried out for both salts, and the ΔH values of the dehydration step were estimated to be 64.4 kJ mol−1 for 1 and 73.0 kJ mol−1 for 2.