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- Hedeland, Ylva, et al.
(författare)
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Effect of alkali metal hydroxides on the enantioseparation of amines using di-O-isopropylidene-keto-L-gulonic acid as the selector in NACE
- 2006
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 27:22, s. 4469-4479
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Tidskriftsartikel (refereegranskat)abstract
- The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (-)-2,3:4,6-di-O-Isopropylidene-2-keto-L-gulonic acid ((-)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines; (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (-)-DIKGA, for Li+, Na+ and Cs+ with (-)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH.
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- MacMillar, Susanna, et al.
(författare)
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Solvent effects on ion pairing of tetra-n-butylammonium cyanide : A conductometric study
- 2008
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Ingår i: Journal of Physical Organic Chemistry. - : Wiley. - 0894-3230 .- 1099-1395. ; 21:3, s. 237-241
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Tidskriftsartikel (refereegranskat)abstract
- Tetra-n-butylammonium cyanide (n-Bu4NCN) is a commonly used reagent, for example, for the synthesis of nitriles. Recently n-Bu4NCN has been used as the nucleophilic reagent in kinetic isotope effect studies of nucleophilic aliphatic substitution reactions. The present research concerns the aggregation status (dissociated ions, ion pairs, higher aggregates) and transport properties of n-Bu4NCN in water, dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF), at 25 C as studied by means of precision conductometry. These properties are of great importance since both non-polar and dipolar aprotic solvents are commonly used in the applications. In water as solvent the equilibrium constant for ion-pair formation, K-p =10.1 and the limiting molar conductivity, Lambda(o)= 102.4 cm(2) Omega(-1) mol(-1). The corresponding values for DMSO are K-p =1.98 +/- 0.19 and Lambda(o) = 34.59 +/- 0.03 cm(2) Omega(-1) mol(-1). These data imply that the degree of dissociation, in contrast to the expectations, is higher in DMSO than in water at the same salt concentration. In THF, the conductance as a function of concentration shows a minimum typical for solvents with low relative permittivity, indicating the formation of higher aggregates. The equilibrium constant for ion-pair formation and conductivity in THF is K-p=58.4 X 10(3) and Lambda(o)=9.81 cm(2) Omega(-1) mol(-1).
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