Ethylammonium Perchlorate Research Articles

Thermodynamic and NMR studies of solvent effect on enantiomeric recognition for chiral organic ammonium guests by chiral diketopyridino-18-crown-6 type ligands at 25.0°C

Abstract Three chiral diketopyridino-18-crown-6 type macrocycles have been shown to exhibit a high degree of enantiomeric recognition toward α-(1-naphthyl)ethylammonium perchlorate (NapEt) in various ratios of chloroform/methanol (CDCl3/CD3OD) and 1,2-dichloroethane/methanol (C2H4Cl2/CH3OH) solvent mixtures (from 100% to 10% methanol component). In most cases, differences in log K values (Δlog K) for (R)− and (S)-NapEt complexation with the chiral macrocycles are larger than 0.5. The degree of the enantiomeric recognition indicated by the Δlog K value changes noticeably with the binary solvent components. The recognition is better in the solvents having a moderate methanol component than in the binary solvents having either a high or a low methanol component. The highest degree of recognition is observed in 6/4 (v/v) CDCl3/CD3OD and C2H4Cl2/CH3OH solvent mixtures and in a 7/3 (v/v) C2H4Cl2/CH3OH mixture for chiral (S,S)-1 macrocycle. Thermodynamic parameters determined in solvent mixtures of C2H4Cl2/CH3OH...

Chiral Pyridine-Based Macrobicyclic Clefts: Synthesis and Enantiomeric Recognition of Ammonium Salts.

An achiral (3) and two chiral pyridine-based macrobicyclic clefts (4 and 5) have been prepared by treating 2,6-bis[[2',6'-bis(bromomethyl)-4'-methylphenoxy]methyl]pyridine (2) with the appropriate achiral and chiral glycols. Starting 2 was prepared by first treating 2,6-bis(hydroxymethyl)-4-methylphenol with 2,6-[(tosyloxy)methyl]pyridine followed by phosphorus tribromide. Achiral macrobicyclic cleft 3 formed a complex at 25 degrees C in 50% CH(3)OH/50% CHCl(3) (v/v) with a primary ammonium salt (log K = 3.15) as evidenced by a significant change in the (1)H NMR spectrum. Highly organized (S,S,S,S)-4, prepared by treating 2 with (1S,5S)-3-oxapentane-1,5-diol, exhibited recognition at 25 degrees C in 20% C(2)H(5)OH/80% 1,2-C(2)H(4)Cl(2) (v/v) for the (S)-enantiomer of alpha-(1-naphthyl)ethylammonium perchlorate (NapEt) over its (R)-form (Delta log K = 0.85). This high recognition factor probably reflects an increase in molecular rigidity by the introduction of a second macro ring on the monocyclic pyridinocrown ligand.

A thermodynamic study of enantiomeric recognition of organic ammonium cations by pyridino-18-crown-6 type ligands in methanol and a 1: 1 methanol-1,2-dichloroethane mixture at 25.0�C

LogK, ΔH, andTΔS values for interactions of (R) and (S) enantiomers of α-(1-naphthyl)ethylammonium perchlorate (NapEt), α-phenylethylammonium perchlorate (PhEt), and the hydrogen perchlorate salt of 2-amino-2-phenylethanol (PhEtOH) with a series of chiral and achiral pyridino-18-crown-6 type ligands and 18-crown-6 (18C6) were determined from calorimetric titration data valid in methanol and in a 1: 1 (v/v) methanol-1,2-dichloroethane (MeOH-1,2-DCE) mixture at 25.0°C. In the MeOH-1,2-DCE solvent mixture, the chiral macrocyclic ligands exhibit excellent recognition for enantiomers of the three organic ammonium cations as shown by large differences in logK values (Δ logK) which range from 0.4 to 0.6 (2.5- to 4.0-fold difference in binding constants). The Δ logK values in the solvent mixture MeOH-1,2-DCE are increased by 0.1–0.5 logK units over those in absolute methanol, indicating a favorable effect of 1,2-dichloroethane on enantiomeric recognition. In 1,2-dichloroethane, however, the interactions are too strong (logK>6) to observe the degree of recognition by a direct calorimetric method. Complexation of organic ammonium cations by these macrocyclic ligands is driven by favorable enthalpy changes. The entropy changes ure unfavorable in all cases. The thermodynamic origin of enantiomeric recognition for NapEt in 1:1 (v/v) MeOH-1,2-DCE is enthalpic, but those for PhEt and PhEtOH are entropic. Effects of the ligand structure and flexibility and of the organic cation structure on recognition and complex stability are discussed on the basis of the thermodynamic quantities. Different thermodynamic behaviors of achiral 5 and 18C6 from those of chiral macrocyclic ligands indicate a difference between chiral and achiral macrocycle interactions with the chiral organic ammonium cations. The different thermodynamic behavior of NapEt enantiomers compared to those of PhEt and PhEtOH enantiomers supports the idea that the solution complex conformation of NapEt is different from those of PhEt and PhEtOH. π-π interaction is absent for the PhEt and PhEtOH complexes with diesterpyridino-18-crown-6 ligands in solution. Therefore, the higher degree of enantiomeric recognition for NapEt than for either PhEt or PhEtOH by these chiral macrocyclic ligands is a result of the presence of π-π interaction in the NapEt system.

Thin Layer Chromatographic Studies of Some Sulpha Drugs Substituted Pyrazoles Using Silica Gel-G Plates Impregnated with Various Adsorbents

Abstract Present communication describes the resolution of some Sulpha drugs substituted synthesized pyrazole derivatives on Silica gel-G plates impregnated with various adsorbents viz; sodium lauryl sulphate, Tetra ethyl ammonium perchlorate, Tetrabutyl ammonium bromide, Tetrabutyl ammonium hydroxide and Triton X-100.