Chemical separations by distillation and chiral high performance liquid chromatography by Qiqing (Max) Zhong A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Chemistry Program of Study Committee: Walter S. Trahanovsky, Co-major Professor Daniel W. Armstrong, Co-major Professor Robert S. Lin Yan Zhao Iowa State University Ames, Iowa 2006 Copyright © Qiqing (Max) Zhong, 2006.
All right reserved. UMI Number: 3243568 UMI Microform 3243568 Copyright 2007 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code.
ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 ii To My parents, who raised me and encouraged me, My teachers, who educated me and enabled me, My siblings, who challenged me and supported me, and My wife, who loves me and completed me. iii TABLE OF CONTENTS ABSTRACT.2 Quantitative 13C NMR Analysis .5 Chiral Liquid Chromatography.1 Macrocyclic chiral selectors .2 Polymeric chiral selectors .3 π-π Association chiral selectors.4 Ligand exchange chiral selectors .5 Miscellaneous and hybrid chiral selectors .6 Cyclodextrins and Their Derivatives .7 Chiral Recognition Mechanism. UNUSUAL DISTILLATION BEHAVIOR OF A MIXTURE OF VOLATILE FATTY ACIDS IN DILUTE AQUEOUS SOLUTION.
ANALYSIS BY QUANTITATIVE 13 C NMR.1 Chemicals and instruments .2 Fractional distillation of dilute aqueous solution of three acids .3 Results and Discussion .1 Quantitative 13C NMR analysis method development.2 Distillation of three acids. Additional distillation data. CHROMATOGRAPHIC EVALUATION OF THE POLY (TRANS-1,2- CYCLOHEXANEDIYL-BIS ACRYLAMIDE) AS A CHIRAL STATIONARY PHASE FOR HPLC.3 Results and discussion .1 The structure of P-CAP chiral selectors.3 Reversal of elution order.4 Interactions for chiral recognition. DEVELOPMENT OF DINITROPHENYLATED CYCLODEXTRIN DERIVATIVES FOR ENHANCED ENANTIOMERIC SEPARATIONS BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY.3 Results and Discussion .1 Structures of the CSPs .3 Interactions for chiral recognition.
OPTIMIZATION OF THE SYNTHESIS OF 2,6-DINITRO-4- TRIFLUOROMETHYLPHENYL ETHER SUBSTITUTED CYCLODEXTRIN BONDED CHIRAL STATIONARY PHASES .3 Results and Discussion .1 Structures of the CSPs. 204 vi ABSTRACT The purpose of this research was to explore a convenient method for bulk separations of volatile fatty acid (VFA) mixtures in dilute aqueous solution, and to develop new chiral stationary phases (CSPs) for enantiomeric separations by high-performance liquid chromatography (HPLC). Direct separations of acetic, propionic, and butyric acids in dilute water solution by azeotropic distillation were demonstrated. Despite of its highest boiling point among these three acids, the butyric acid is the first acid to distill, followed by propionic acid.
Over half of acetic acid still remains in the pot even when the other two acids are gone. Quantitative carbon-13 nuclear magnetic resonance (NMR) was employed as an effective and accurate detecting method for the acid mixtures. A comparison of short (1 second) vs. long (30 seconds) delay (D1) between successive scans was made.
The effects of a paramagnetic reagent, disodium (diethylenetriaminepentaacetato)iron(III) (Na2[Fe(DTPA)]), and its concentration on the quantitative carbon-13 analysis was also discussed. The basis for most chiral high performance liquid chromatographic separations is the chiral stationary phases. The design, synthesis and evaluation of new chiral stationary phases are the other important part of this research. We first evaluated the chromatographic performance of the polymeric (R,R) and (S,S) poly (trans-1,2-cyclohexanediyl-bis acrylamide) based CSPs, which are known as (R,R) and (S,S) poly-cyclic amine polymer (P-CAP) HPLC columns.
These two columns are effective in separating enantiomers under normal phase and polar organic conditions, and with mobile phases containing halogenated solvents. The retention behavior, effects of mobile phase vii additives, normal-phase organic modifier, flow rate, column efficiency under different mobile phase conditions, sample loading capacity, and reversal of analyte elution order are discussed in detail. Hydrogen bonding interactions between these CSPs and analytes are the dominant interactions for chiral recognition by P-CAP columns. Dipole-dipole interactions and steric repulsion may also contribute to enantiomeric separations.
For the first time, we prepared stable β-cyclodextrin (β-CD) derivatives which contain π-electron deficient substituents (i., π-acidic moieties) for enantiomeric separations by HPLC. A variety of different dinitro-substituted aryl groups are investigated and compared in terms of their enantioselectivity. These CSPs are highly stable and robust under three mobile phase modes, including the reversed-phase, normal phase, and polar organic modes and exhibit very broad selectivity for a wide variety of compounds, including heterocyclic compounds, chiral acids, chiral amines, chiral alcohols, chiral sulfoxides and sulfilimines, amino acid derivatives, and other chiral compounds. The effects of the mobile phase pH, buffer composition, number and position of the dinitro groups on the phenyl ring substituent, degree of substitution, and the bonding strategy on the chromatographic performance of the CSPs are investigated.
The 2,6-dinitro-4-trifluoromethylphenyl (DNP-TFM) substituted β- cyclodextrin-based CSPs have the best column performance overall. For each mobile phase mode, no degradation in column performance was observed even after more than 1000 injections. Finally, we optimized the 2,6-dinitro-4-trifluoromethylphenyl derivatized β- cyclodextrin-based CSPs for enhanced enantiomeric separations. Five different CSPs, which differ from each other in the linkage chain, the position of DNP-TFM groups on β-CD ring, or the sequence of synthetic procedure, were prepared and evaluated with 14 pairs of viii enantiomeric analytes in the reversed-phase mode.
The spacer effect is much more pronounced for the β-cyclodextrin derivatives with the DNP-TFM substituted only on the secondary hydroxyl groups. The synthetic sequence of derivatization and bonding chemistry also affects the chiral recognition capability of the CSPs. The optimized CSP based on DNP- TFM derivatized β-CD exhibits broad enantioselectivity and high separation efficiency which makes it one of the most useful derivatized cyclodextrin CSPs. GENERAL INTRODUCTION Chemical separations are widely utilized in process industries.
In manufacturing, separation processes are used to remove impurities from raw materials, purifying products, recycling chemical streams, and protecting environments, etc [1]. Due to the fact that separation processes can cost from 40% to 70% of both capital and operating expenditures, significant savings can be achieved by application of the proper separation technology [1]. The common chemical separation technologies include distillation, extraction, crystallization, adsorption, chromatography, ion exchange, membranes, electrical and other field-induced separations, etc. This research focuses on the separation of organic molecules by distillation and chiral high performance liquid chromatography.1 Distillation Distillation is a chemical separation method which utilizes different boiling points to separate and purify a liquid component from a mixture.
So, it is suitable for the separation of the components, in the liquid mixture, which have different vapor pressures, or boiling points. Due to the fact that distillation has a simple process flowsheet, and is a low-risk and low- capital-investment process, about 90% to 95% of all the chemical process industry separations are achieved by distillation [1]. In a distillation column, the countercurrent flow of vapor and liquid mix together. Trays or packings are usually used inside the column to improve interfacial contact of the two phases.
Despite its low energy efficiency and the requirement of thermal stability of analytes at their boiling points, distillation is still favored for volatile analytes against other separation methods. 2 An azeotrope is a liquid mixture of two or more components which has the same composition for both vapor and liquid states when it is distilled at a certain pressure [2,3]. Therefore, it is impossible to completely separate the azeotropic components into individual compound by simple distillation. However, it is still possible to separate several azeotropes from each other by distillation, provided they have different boiling points.
In view of the limited supply of petroleum and fossil fuels, it is of great interest to obtain valuable organic compounds, such as volatile fatty acids (VFA), from biorenewable resources [4-7]. These volatile fatty acids, including acetic, propionic, and butyric acids, exist as a dilute mixture in the anaerobic fermentation sludge [8]. Distillation may provide a convenient way to separate these acids out of the mixture, furthermore, possibly from each other. Azeotropic data of these three acids with water are shown in Table 1 [3,9].2 Quantitative 13C NMR Analysis The nuclear magnetic resonance (NMR) was discovered by Bloch [10,11] and Purcell [12,13] independently in 1945.
It is a sophisticated technique which measures the absorption and emission of electromagnetic radiofrequency radiation by the nuclei of certain atoms that are placed in a strong magnetic field [14,15]. Because abundant information on the atomic interactions within or between organic compounds and/or macromolecules can be revealed by NMR, it is of major importance not only in molecular structure determination [16], but also in molecular binding studies [17]. Among hundreds of atoms and their isotopes, the most commonly measured atomic species in NMR are 1H, 13C, 15N, 19F and 31P. Due to the low natural abundance of 13C (only 1.1%), either 13C-enriched and/or highly concentrated samples, or long acquisition times are required for a 13C spectra with sufficient signal-to-noise ratio (S/N).
Moreover, different type of carbons may have significantly 3 different relaxation times, which could range from hundreds of milliseconds to over 100 seconds [18]. The wide spread of 13C relaxation times leads to preferential saturation of the more slowly relaxing 13C nuclei. Consequently, the signal intensities acquired by the NMR spectrometer for the same amount but different types of 13C nuclei may vary [16]. This makes 13C NMR difficult for quantitative analysis.
The difficulty can be overcome in different ways. First, the pulse delay between repetitions of scans can be set long enough to ensure that every carbon relaxes back to Boltzmann equilibrium before the next radiofrequency pulse is applied [19]. This method may suffer from long analysis time. Second, adding a paramagnetic reagent, such as Fe3+, Cr3+, Gd3+, Mn2+,Eu3+, etc.
can significantly suppress the nuclear Overhauser effect (NOE) and shorten the 13C spin-lattice relaxation times (T1) of all carbons so that differences in T1 become insignificant [16,20-22]. The NOE is unfavorable for quantitative 13C analysis because it perturbs signal intensities of different carbons. The NOE can be further suppressed by a gated decoupler [16]. The decoupler is turned on during data acquisition and off during the pulse delay.3 Chromatography Analytical separations largely relied on precipitation, crystallization, distillation, and extraction before the middle of twentieth century.
However, since then, chromatography has become a powerful and widely used analytical method which finds widespread applications in research and industry [23,24]. The Russian botanist Micaël S. Tswett demonstrated the separation of plant pigments by liquid column chromatography in 1903 [25]. Because of his innovative work, Tswett is regarded as the father of chromatography [26].
In 1952, the Nobel Prize in chemistry was 4 awarded to Archer J. Martin and Richard L. Synge for their invention of partition chromatography and the related plate theory [27]. A total of twelve Nobel Prizes between 1937 and 1972 were awarded to the scientists whose work were largely based on chromatography [28].
This fact clearly shows the extensive applications of chromatography in almost all branches of science. Numerous varieties of chromatography, from paper chromatography, thin-layer chromatography (TLC), gas chromatography (GC), high- performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC), to capillary electrochromatography (CEC), have been developed. The successful development of chromatography directly or indirectly triggered the development of many detection methods, such as flame ionization detector (FID), electron-capture detector (ECD), mass spectrometry (MS), etc. This revolution successfully led analytical chemistry from gravimetric and titration-based wet chemistry to modern instrumental analysis.
The first century of chromatography (from 1903 to 2003) has tremendous fascinating stories [29,30]. Chemists, as well as scientists in other areas, have been benefiting, and will continue to benefit from this powerful and versatile analytical method. New technologies based on chromatography continue to be developed.4 Chirality Louis Pasteur first proposed molecular asymmetry in 1848 to explain the crystal morphological principles introduced by René J. The four valences of a carbon atom form a tetrahedron structure with the carbon atom as its center was first proposed by Jacobus H.
van't Hoff and Achille Le Bel in 1874, independently [32]. These hypotheses are considered to be the origin of stereochemistry and they gave rise to the concept of chirality in chemistry, i. the asymmetric geometry of molecules.