Document Type

Dissertation - Open Access

Award Date

2018

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas E. Raynie

Keywords

Deep eutectic solvents, DES, DFT simulations, Hydrogen-bonding, Solvatochromics, Solvent Chemistry

Abstract

Various forms of deep eutectic solvents have been synthesized with advantages of 100% atom economy, low vapor pressure, ease of preparation, cost efficiency, low toxicity, and tunability. Though several DESs have been synthesized and characterized, including binary and ternary solvents, none of the binary DESs have been formulated with water as the sole hydrogen bond donor(HBD). This is due to a couple of opinions. First, water is disruptive to the eutectic bond in tertiary DES. Secondly, the ubiquity and concentration of water even in natural systems have led to the assertion that a solution rather than a eutectic solvent will be formed. The aims of the study were to explore the use of water as the sole HBD in the formulation of type III DES and to exploit the small size of water molecules to further probe the nature of the eutectic bonding system in DESs. To achieve these aims, a system of solvents made up of choline chloride and water at varying molar ratios of water were formulated and characterized. The solvents included ChCl:H2O (1:1) through to ChCl:H2O (1:10) with the ratio of water increasing by one. Spectroscopic analyses and physicochemical analyses were carried out to ascertain intermolecular hydrogen bonding between the choline chloride and water, as well as characterize the solvents. Also, molecular dynamic simulation (MDS) coupled with density functional theory were used to probe the nature of the interactions within the solvents formulated. The results of the spectroscopic analyses indicated shifts in peaks and bands associated with weak hydrogen bond interactions. This was significant as it provides evidence of DES formation from the choline chloride and water. The largest shifts came in the ChCl:H2O (1:3) followed by ChCl:H2O (1:4). This suggested that the eutectic formulation is ChCl:H2O 1:3. Freezing and melting point determinations confirmed the eutectic composition to be ChCl:H2O (1:3) with eutectic point of -84.7°C. The ChCl:H2O (1:4) followed with freezing point of -82.9°C. The thermal stability studies involving DSC and TGA were as predicted, as the ChCl:H2O (1:3) and ChCl:H2O (1:4) solvents exhibited high decomposition temperatures and high stabilities commensurate with the observed strengths of the hydrogen bonds found in the spectroscopic analyses. The molecular dynamic and DFT simulations affirmed the formation of hydrogen bonding between the QAS and HBD in the order of the strengths observed in the spectroscopic analyses. Also, the simulated charge transfer analyses from Hirshfeld partial charges and Voronoi’s deformation density charges indicate charge spreading from the chloride anion onto the organic backbone of the choline cation and HBD to facilitate the formation of Hydrogen bonds between the chloride ion and the HBD leading to DES formation. It is important to mention that other weaker interactions may also play a less significant role.

Library of Congress Subject Headings

Solvents.
Solvents -- Environmental aspects.
Green chemistry.
Choline.
Chlorides.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

174

Publisher

South Dakota State University

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Rights Statement

In Copyright