Author

Mohsen Talebi

ORCID Identifier(s)

0000-0002-1951-8163

Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Daniel W Armstrong

Abstract

Ionic Liquids (ILs) are state-of-the-art fluids that have found broad application in separation science. Owing to their unique physicochemical properties such as low vapor pressure, high thermal stability, and high viscosity, they were successfully used as stationary phase in gas chromatography (GC). By properly engineering their molecular structure, ionic liquids with tailor-made properties can be designed. Therefore, a systematic structure-function relationship can be established to study the effect of structural modification on the properties of ionic liquids. Herein, I describe the design and synthesis of several dicationic ionic liquids. The synthesized ILs were characterized in terms their physicochemical properties. The effect of different structural on their physicochemical properties variations was investigated. The selected ILs with highest thermal stabilities were utilized as GC stationary phase. Comparing the separation patterns of different compounds on these columns provided some insight about the effects of structural variations on the selectivities and polarities of dicationic ILs. Due usually show higher melting points than conventional ILs. This increase in melting temperature narrows their utilization in some applications. To overcome this limitation, a systematic study was performed to fine-tune the properties of DILs by utilizing branched spacer linkage between two cationic head groups. A series of dicationic ionic liquids containing α-, β-, and γ-substituents on the alkane linkage chain were synthesized, and the effect of a substituent position on their physicochemical properties was evaluated. ILs with optimal properties they were coated on fused silica capillaries and evaluated for separation of fatty acid methyl esters (FAMEs). These novel stationary phases demonstrated excellent selectivity for separation of cis and trans, as well as omega-3 and omega-6 positional FAME isomers. The detailed analysis of cis and trans C18:1 isomers of a partially hydrogenated vegetable oil demonstrated the enhanced separation of FAMEs on the IL-based columns compared to the American Oil Chemists Society (AOCS) official method. Further tuning of dicationic ILs properties was obtained using different accompanying anions. Combination of branched-chain dicationic moiety with fluorosulfonyl derivatized anions led to formation of highly polar ionic liquid stationary phases, with a McReynolds polarity passing 6000. These ILs showed unique selectivity for separation of FAMEs from biodiesel and bacterial sources.

Keywords

Ionic liquid, Polar GC stationary phase, Selectivity, Physicochemical properties

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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