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SYNTHESIS AND CHARACTERIZATION OF DEEP EUTECTIC (DES) WITH MULTIFUNCTIONAL BUILDING BLOCKS

A Thesis Presented to The graduate faculty of the University of Akron

In Partial Fulfillment of the Requirements of the Degree Master of Science

Yi Ting Lo August, 2019 SYNTHESIS AND CHARACTERIZATION OF DEEP EUTECTIC SOLVENTS (DES) WITH MULTIFUNCTIONAL BUILDING BLOCKS

Yi-Ting, Lo

Thesis

Approved: Accepted:

______Nicole Zacharia Department Chair Advisor Dr. Sadhan C. Jana

______Dr. Kevin Cavicchi Committee Member Interim Dean of the College Dr. Ali Dhinojwala

______Xiong Gong Dr. Dean of the Graduate School Committee Member Dr. Chand Midha

______Date

ii ABSTRACT

Ionic have attracted interest as non-volatile liquids for numerous applications. An alternative material are deep eutectic (DES) generated by mixing interacting crystalline species to generate a eutectic with a point below room . In this thesis DESs were prepared by mixing quaternary ammonium compounds and diacids, which interact through hydrogen bonding.

Mono- and di-functional quaternary ammonium compounds were either purchased or synthesized and mixed with different aliphatic dicarboxylic . The overarching goal of this work was to investigate DES formation from difunctional quaternary ammonium and dicarboxylic compounds to determine if polymeric-like DES could be obtained, with corresponding polymeric like properties (i.e. viscoelasticity, high , formation). Differential scanning calorimetry and optical microscopy were used to investigate the behavior of the different quaternary ammonium/acid pairs to determine the structural features that contribute to deep eutectic formation.

iii ACKNOWLEDGEMENT

I would like to express my sincere gratefulness to my advisor Professor Nicole

Zacharia and Kevin Cavicchi for his constant guidance, encouragement and selfless support on my research. It is a great honor and pleasure for me to be a member of his group and to work as a graduate student under his instruction.

I would like to acknowledge all my group members, especially Tzu Yu Lai for her kind help and suggestions on my work. My studies would not be completed without their help.

I would like to thank Prof. Zacharia, Prof. Cavicchi and Prof. Xiong Gong for being my committee members.

Lastly, I would express my deepest appreciation for my beloved my parents for their support throughout all these years that I have studied abroad.

iv TABLE OF CONTENTS

Page

LIST OF TABLES………………………………………………………………………………….……………………viii

LIST OF FIGURES…………………………………………………………………………….…………………………ix

CHAPTER

I. INTRODUCTION…….……………………………………………………………………….………………………1

1. Overview…………………………………………………………………………………………………………..1

1.1 Background……..………………………………………………………………..………………………..1

1.2 Traditional ionic liquids (ILs)…………………………….………………………………..…….….2

1.3 Deep eutectic solvents (DESs)………………………..……………………………………….…..3

1.4 …………………………………………………………………………………….………5

1.5 Eutectic point…………………………………………………………………..………………………….7

1.6 Types of DESs………………………………………………………..…………………..………………..7

1.7 Hole theory…………………………………………………………..………………………..…………..9

1.8 Properties of DESs………………………………………………………………………..……………10

1.9 Applications of DESs………………………………………………………………………….………16

2. Differential scanning calorimetry (DSC)…………………………………..……………….………22

v 3. Nuclear magnetic resonance spectroscopy (NMR)…………………..……………………..23

4. Polarized optical microscopy (POM)………………………………………………………………..24

II. Experiment I…………………….…………………………………………………..………………………….…25

1. Introduction……………………………………………………………………………..…………………….25

2. Experimental section………………………………………………………………..…………………….25

2.1 Materials………………………….………………………………………………….……………………25

2.2 Preparation of ………………………………………………..……….26

2.3 Illustration of phase diagrams…………………………………………………..……………….27

3. Result and discussion……………………………………………………………………………..……….27

3.1 Adipic acid + tetra-n-butylammonium bromide……………………………………..….28

4. Conclusion……………………………………………………………………………………………..……….31

III. Experiment II………………………………………………………………………………….……..…………..33

1. Introduction………………………………………………………………………………..………………….33

2. Experimental section………………………………………………………………………………..…….34

2.1 Materials………………………………………………………………………………………..…………34

2.2 Synthesis……………………………………………………………………………………….……..……35

2.3 Characterization……………………………………………………………………..…………………39

3. Result and discussion…………………………………………………………………..………………….43

3.1 Visual observation…………………………………………….……………………..……….………44

vi 3.2 Polarized optical microscopy (POM)…………………….…………………..……….………46

3.3 1H NMR…………………………………………………………………………………………….....……47

3.4 Differential scanning calorimetry (DSC)………………………………………..……………53

IV. Conclusion……………………………………………………………………………………..………..……….58

REFERENCES…………………………………………………………………….……………………………………..59

vii LIST OF TABLES

Tables Page

1.1 General Formula for the Classification of DESs[3]…………………….…………………….…….8

2.1 Melting points of products with different ratio of materials…………..…………….……30

viii LIST OF FIGURES

Figure Page

1.1 Material and synthesis process of deep eutectic solvents[13]……………………………….2

1.2 Typical structures of the donors and acceptors[2]………………………..4

1.3 Optimized conformation of hydrogen bonding between HBD and HBA in deep

eutectic solvent[1]………………………………………………………………………………………………..5

1.4 Schematic representation of a eutectic point of binary [3]……………6

1.5 points of chloride with five carboxylic acids[2]…………………………12

1.6 Relationship between viscosity and temperature of multiple types of different

kinds of DESs[13]…………………………………………………………………………………………………14

1.7 of the /ChCl DES as a function of the molar ratio[2]………………..16

1.8 The correlation between the CO2 adsorption of polyDEM and [1]…………18

1.9 Glycerol in an AcChCl–glycerol in contact with

containing glycerol as a function of time[2]………………………………………………………..20

1.10 Material under normal microscopy………………………………………………………………….24

1.11 Material under polarized microscopy………………………………………………………………24

2.1 Structure of adipic acid……………………………………………………………………………………..26

ix 2.2 Structure of Tetra-n-butylammonium bromide………………………………………………….26

2.3 Photo of Pyris DSC8500 machine………………………………………………………………………27

2.4 DSC figures from 0-50% mole percentage of adipic acid……………………………………28

2.5 DSC figures from 0-50% mole percentage of adipic acid……………………………………29

2.6 Phase diagram of DES composed of adipic acid and tetra-n-butylammonium

bromide…………………………………………………………………………………………………………….30

2.7 Freezing points of choline chloride with five carboxylic acids[2]…………………………32

3.1 Structure of adipic acid……………………………………………………………………………………..34

3.2 Structure of succinic acid…………………………………………………………………………………..34

3.3 Structure of dodecanedioic acid………………………………………………………………………..34

3.4 Structure of (Br-Ph-(N(Bu)3)2)…………………………………………………………………………….35

3.5 Structure of (Br-Ph-(N(Oct)3)2)…………………………………………………………………………..35

3.6 Photo of (Br-Ph-(N(Bu)3)2)………………………………………………………………………………….36

3.7 NMR figure of (Br-Ph-(N(Bu)3)2)…………………………………………………………………………37

3.8 Photo of (Br-Ph-(N(Oct)3)2)………………………………………………………………………………..38

3.9 NMR figure of (Br-Ph-(N(Oct)3)2)……………………………………………………………………….38

3.10 Schematic representation of a eutectic point of binary eutectic system[3]……….44

3.11 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) at initial………….45

3.12 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) after 1 hour…….45

x 3.13 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) after 2 hours…..45

3.14 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Bu)3)2)……………………46

3.15 POM figure of 60 mole% adipic acid+40 mole% (Br-Ph-(N(Bu)3)2)……………………46

3.16 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Oct)3)2)…………………..47

3.17 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Oct)3)2)…………………..47

3.18 NMR figure of (Br-Ph-(N(Bu)3)2)……………………………………………………………………….47

3.19 NMR figure of (Br-Ph-(N(Oct)3)2)……………………………………………………………………..48

3.20 NMR figure of adipic acid………………………………………………………………………………..48

3.21 NMR figure of succinic acid……………………………………………………………………………..48

3.22 NMR figure of dodecanedioic acid…………………………………………………………………..49

3.23 NMR figure of 40 mole% adipic acid + 60 mole% (Br-Ph-(N(Bu)3)2…………………..49

3.24 NMR figure of 50 mole% adipic acid + 50 mole% (Br-Ph-(N(Bu)3)2……………………49

3.25 NMR figure of 60 mole% adipic acid + 40 mole% (Br-Ph-(N(Bu)3)2……………………50

3.26 NMR figure of 40 mole% succinic acid + 60 mole% (Br-Ph-(N(Bu)3)2………………..50

3.27 NMR figure of 50 mole% succinic acid + 50 mole% (Br-Ph-(N(Bu)3)2………………..51

3.28 NMR figure of 60 mole% succinic acid + 40 mole% (Br-Ph-(N(Bu)3)2………………..51

3.29 NMR figure of 50 mole% dodecanedioic acid + 50 mole% (Br-Ph-(N(Bu)3)2……..51

3.30 NMR figure of 70 mole% dodecanedioic acid + 30 mole% (Br-Ph-N(Oct)3)2……..52

3.31 DSC figure of adipic acid+(Br-Ph-(N(Bu)3)2) (endo up)………………………………………53

xi 3.32 DSC figure of succinic acid+(Br-Ph-(N(Bu)3)2) (endo down)………………………………54

3.33 DSC figure of dodecanedioic acid+(Br-Ph-(N(Bu)3)2) (endo down)……………………54

3.34 DSC figure of adipic acid+(Br-Ph-(N(Oct)3)2) (endo up)…………………………………….55

3.35 DSC figure of succinic acid+(Br-Ph-(N(Oct)3)2) (endo down)…………………………….55

3.36 DSC figure of dodecanedioic acid+(Br-Ph-(N(Oct)3)2) (endo down)………………….56

3.37 XRD figure of the material and the DES product………………………………………………57

xii CHAPTER I

INTRODUCTION

1. Overview

1.1 Background

The traditional ionic liquids (ILs) had been used for many years, and had been considered as “green solvents” due to their low pressure and high point, which make them convenient to recycle. However, the term “green” has been challenged in recent research. Several disadvantages had been found in ILs such as hazardous toxicity, very poor biodegradability, and high cost for the purification process. In addition, ILs requires large amount of materials in order to complete the process of synthesis. Thus, to overcome those disadvantages of ILs, a new type of solvent called Deep Eutectic Solvent (DES) is designed, as an alternative of traditional ionic . The DES has similar properties with common ILs, but cheaper, safer, non- toxicity, biodegradable and biocompatible, and lower cost during synthesis.

1 Figure 1.1 Material and synthesis process of deep eutectic solvents. Adapted with permission from reference[13] ACS Sustainable Chem. Eng. 2014, 2, 2416−2425

Copyright (2014) American Chemical Society.

1.2 Traditional ionic liquids (ILs)

Before the designation of deep eutectic solvents, the solvents we used were the ionic liquids. Here’s a brief introduction of it

Originally, ionic liquids were defined as liquids that were consisted of and stayed at liquid state at the temperature below 100℃.

There are basically two generations of ionic liquids:

The first generation ones are basically the eutectic that are composed of

metal halides such as AlCl3 and ZnCl2, and organic salts. In this sort of ionic liquids, they form an eutectic composition at certain ratio, just like deep eutectic solvents.

During the synthesis process of this sort of ionic liquids, there are bulky composites such as chloroaluminate formed. Once the bulky structures were formed, the charge 2 of the ions will be reduced, and so does the of the liquid system. As a result, the melting points of the fluids will be reduced consequently.

Though we successfully formed various ionic liquids with these materials and methods, this generation of ionic liquids have several disadvantages, such as air and moisture stability.

The second generation ionic liquids were discovered by Wilkes and Zaworotko.

Instead of forming eutectic composites with metal halides and organic salts, this sort of solvents were composed of discrete ions such as .

In the second generation ionic liquids, the problems that were formed in the first generation ionic liquids (e.g. air and moisture stability issue) can be reduced by the discrete anions (e.g. PF6) since those anions are more hydrophobic.

To summarize, the first generation ionic liquids are those based on eutectic compositions and the second generation are those composed of discrete ions.

1.3 Deep eutectic solvents (DESs)

Now let’s talk about the deep eutectic solvents. Like traditional ionic liquids, deep eutectic solvents are fluids that were formed by materials with low lattice energy, which then make their melting points low. However, instead of forming through ionic bonds, deep eutectic solvents are composed of hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA), which are connected via hydrogen bonds. And

3 through hydrogen bond, charge delocalization happens between the bonding of the on the hydrogen bond donors and the halide (e.g. Cl-, Br-) on the hydrogen bond acceptors, and consequently to the reduction of the melting points.

Here are some typical hydrogen bond donors and halide salts (hydrogen bond acceptors):

Figure 1.2 Typical structures of the hydrogen bond donors and acceptors. Adapted with permission from reference[2] Chem. Soc. Rev., 2012, 41,7108–7146. Copyright

(2012) Royal Society of Chemistry

And the hydrogen bonding sites between the materials:

4 Figure 1.3 Optimized conformation of hydrogen bonding between HBD and HBA in deep eutectic solvent. Adapted with permission from reference[1] Macromol. Rapid

Commun. 2016, 37, 1135-1142. Copyright (2016) Wiley.

Take the figure above for example, the combination of HBD and HBA are amidoxime and 2-cholinium bromide methacrylate. There are two sites that the materials can be bonded through hydrogen bond. One is the bromide anion on the

HBA and the hydrogen on the N-OH site of the amidoxime; another site is the hydrogen on the -OH site of the HBA and the nitrogen on the N-OH site of amidoxime.

When talking about deep eutectic solvents, it often involves the understanding of phase diagram and the eutectic point, those are the two things we’re going to briefly introduce:

1.4 Phase diagram[4][35]

A phase diagram is one of the most convenient and efficient ways to represent the equilibrium state of a system. When we illustrate a phase diagram, the complexity of

5 the diagram is mainly determined by the number of components that formed the system (e.g. unary, binary, ternary).

The deep eutectic solvents are generally binary. As for binary mixtures, the phase diagram will become more complicated. Usually the complete diagram for binary mixture is three dimensional, which contains multiple properties such as composition, temperature, pressure. But to simplify, we often assume one magnitude to be constant state, for example, the pressure of the system. Under such assumption, the phase diagram shall become two dimensional, which is much easier to depict.

For deep eutectic solvents, the phase diagram follows the same assumption of constant pressure. For the coordinates, there are “mole ratios of certain material

(HBA or HBD)” on the x axis and “melting ” on the y axis. Here’s a typical example of the phase diagram of deep eutectic solvents:

Figure 1.4 Schematic representation of a eutectic point of binary eutectic system.

6 Adapted with permission from reference[3] Chem. Rev. 2014, 114, 11060−11082.

Copyright (2014) American Chemical Society

As we can see from the figure, at different ratios of HBD and HBA, the melting points of each materials shall alter. And during certain ratio, they will reach a mutual and minimum .

1.5 Eutectic point[2][4]

When synthesizing deep eutectic solvents, we will reach a lowest melting temperature at a certain point with a certain ratio of HBA and HBD, and that point is called the “eutectic point”. Here are some brief introductions on the concept of the term “eutectic”:

When two or more materials are mixed together, at certain ratio, the materials will homogenize into one phase at a certain temperature that is lower than any of the materials’ melting points. Under that condition, the “eutectic system” is formed, and that certain temperature is called the “eutectic temperature”.

1.6 Types of DESs

Now let’s talk about deep eutectic solvent itself. The general formula of deep eutectic solvents is[3]:

+ - Cat X ZY

The Cat+ can be any ammonium, or , cation, and X is generally a

7 halide anion. Both Cat+ and X- we can constantly see in DESs, usually are from the

HBAs (e.g. quaternary ammonium halide salts). Y refers to the Lewis acids (HBDs) that interact with the halide anion, while z means the number of acid that actually interacts with the halide anions through hydrogen bond.

According to Abbott et al., there are generally four types of DESs[3]:

+ - Type I: Cat X zMClx M=Zn, Sn, Fe, Al, Ga, In + - Type II: Cat X zMClX·yH2O M=Cr, Co, Cu, Ni, Fe + - Type III: Cat X zRZ Z=CONH2, COOH, OH

Type IV: MClx+RZ=MClx-1+·RZ+MClx+1 M=Al, Zn Z=CONH2, OH

Table 1.1 General Formula for the Classification of DESs. Adapted with

permission from reference[3] Chem. Rev. 2014, 114, 11060−11082.

Copyright (2014) American Chemical Society

[2][3]The type I DESs is composed of metal chloride and quaternary ammonium salts. This sort of DESs can be considered as an analogous type to the metal halide/imidazolium system that has already been well studied.

Type II DESs is actually pretty similar to type I DESs. But instead of using metal chlorides, they use hydrated metal chloride as one of the materials. This sort of change makes some change on the properties of deep eutectic solvents, which will be mentioned later.

Type III DESs is generally composed of quaternary ammonium salts and various kinds of hydrogen bond donors such as carboxylic acids, alcohols, and amides. The

8 broad range of materials makes them quite versatile in applications. Other than the wide potential window of application, they are also easy to synthesize, low cost, which make their use in industry becomes more and more widespread.

The type IV DESs are quite rare. They are composed of hydrated metal halide composed of certain sorts of transition metals (e.g. zinc, aluminum), and some hydrogen bond donors that are different from those are used in type III DESs, such as , acetamide.

1.7 Hole theory[3]

The hole theory has a certain level of correlation with the properties of deep eutectic solvents such as , here’s some principles and concept of the hole theory. This theory was first proposed by Furth, and expanded by Bockris. In this theory, it is assumed that in ionic materials, there are holes (vacant sites) in the materials while they’re in liquid or molten state. The holes are in random size and location, undergoing constant flux moreover. The equation below can help us determine the size of the holes and ions:

4π(r2) = 3.5 kT/ γ r: radius of the void

γ: surface tension of the liquid k: Boltzmann constant

9 T: absolute temperature (K)

Through calculation, we got to know the average size of the holes is 1.5-2.5Å, and the average size of the ions is 1-2.6Å, the magnitudes are quite similar.

The viscosity of the fluids is affected by the size of the holes in them. At low temperature, the size of the holes is smaller, and the size of the ions becomes relatively big, and the hole size becomes bigger at high temperature. Thus under low temperature, it becomes harder for the ions to move into the vacant places (the

“availability” of the holes is low) , which means the ion mobility was reduced, and the viscosity becomes higher consequently. At high temperature the situation is vice versa.

For ionic liquids and deep eutectic solvents, the optical products are those with low viscosities, that is, with larger holes and smaller ions in the materials. Through the hole theory, we have a chance of synthesizing liquids with such properties, which will make their potential window of applications become wider.

1.8 Properties of DESs

Now we’re talking about several obvious and important properties of deep eutectic solvents.

1.8.1 Melting point[2][3]

One of the most obvious properties of deep eutectic solvents is the change in

10 melting points. Since the materials in DESs are bonded via hydrogen bonds, charge delocalization occurs because of the bonding, which then cause the melting points of the products to decrease.

There are other factors that will affect the depression of melting points. For instance, the decrement of the melting points also relies on the intensity of interaction between the materials: the stronger the interactions are, the larger the decrement will have.

Besides, the sort of materials may also have some influence on the melting points.

For instance, with type I DESs, the melting points of the solvents are approximately

300℃, the decrement is between 200 to 300℃. But when it comes to type II DESs, the decrement becomes larger, though the main difference is that the hydrogen bond acceptor material turns from metal chloride to hydrated metal chloride. It’s probably due to the presence of the . The water in the system decreases the lattice energy, and thus decreases the melting temperatures of the liquids. So the pure metal salts (without water) shall cause smaller depression of the melting point than those with water in it. Additionally, it is shown that materials with lower lattice energy would have lower decrement of melting points, too.

For type III deep eutectic solvents, there is a quite interesting feature of the melting point: When using carboxylic acids as hydrogen bond donors, it is shown that

11 we need two (-OH) groups to coordinate with one halide anion. For instance, if we try to synthesize deep eutectic solvent with choline chloride and , the ratio that will form a liquid with a lowest melting temperature is about 1:2; However, if we use succinic acid, adipic acid, as hydrogen bond donor, the ratio becomes about 1:1.

Thus, for hydrogen bond donors with difunction, the “eutectic ratio” is tend to be closer to 1:1. The figure below shows such tendency:

Figure 1.5 Freezing points of choline chloride with five carboxylic acids. Adapted with permission from reference[2] Chem. Soc. Rev., 2012, 41,7108–7146. Copyright (2012)

Royal Society of Chemistry

12 1.8.2 Viscosity[2]

Another obvious trait that we can observe through our bare eyes is the viscosity of the deep eutectic solvents. Viscosity is also a very important property on DESs that we can do some research on, since it affects the mass transport phenomena quite strongly; besides, liquids with lower viscosities have a wider potential window for industrial application. Thus, synthesizing deep eutectic solvents with lower viscosity is a quite desirable direction in this domain.

There are several factors that affect the viscosity of the deep eutectic solvents:

The high viscosity of the conventional deep eutectic solvents is mainly due to the hydrogen bonding between the HBD and HBA. The intense interaction and bonding between the material would reduce the mobility of the system, thus increase the viscosity of the solvent.

Also, like mentioned previously, at room temperature, deep eutectic solvents often appear as liquids with high viscosities. But the viscosities aren’t invariant. Normally, it is shown that the higher the temperature, the lower the viscosities (Arrhenius-like behavior). That is, the viscosity of the liquids has a negative correlation with temperature. And this phenomena can be described through the equation, which is based on the Arrhenius model, below:

η= η∞ exp(-Ea/RT)

13 η: viscosity of the system (mPa)

η∞: pre-exponential constant (mPa)

Ea: activation energy (KJ mol-1)

From this equation we can also observe that: the higher the activation energy is, the higher the viscosity would be. The activation energy maybe determined by the interaction or the size of the material.

Additionally, the viscosity may be affected by the water content in the product.

Whether the amount is high or low, water seems to have a tendency of promoting an easier and similar flux of the different ions.

Figure 1.6 Relationship between viscosity and temperature of multiple types of different kinds of DESs. Adapted with permission from reference[13] ACS Sustainable

Chem. Eng. 2014, 2, 2416-2425. Copyright (2014) American Chemical Society.

1.8.3 Density[2]

Generally, deep eutectic solvents possess high density. The density is often higher than both the materials that form the DESs. 14 There are several causes that may influence the densities of DESs:

First of all, the higher magnitude to the densities can be explained by the hole theory: Like mentioned previously, it is assumed that there are holes in the system of deep eutectic solvents, just like other ionic materials. By mixing different HBDs and

HBAs together, it might reduce the average radius of the holes (increase the volume of the system), and thus increase the densities of deep eutectic solvents.

Another cause is the sort of the materials. For instance, we can use carboxylic acids as hydrogen bond donors in type III deep eutectic solvent. The chain length

(number of ) will have a negative correlation with the densities, that is, the longer the chain length, the lower the densities. The reason is when the chain length gets longer, so does the molar mass and the molar volume. With higher molar volume, we get lower densities of the products as well.

Besides the effect of hole theory and chain length of HBDs, the content of certain material might also affect densities of the products. Here’s an example of DES composed of glycerol and choline chloride:

15 Figure 1.7 Densities of the glycerol/ChCl DES as a function of the molar composition.

Adapted with permission from reference[2] Chem. Soc. Rev., 2012, 41,7108–7146.

Copyright (2012) Royal Society of Chemistry.

As we can see in the figure, the amount of choline chloride did have an effect on the densities of the products. The more choline chloride we have in the system, the lower the density it will have.

1.8.4 Conductivity

There is a strong relationship between the conductivities and the viscosities of deep eutectic solvents. Due to the general high viscosities of DESs, the liquids often possess a poor conductivity. Thus, it is understandable that the conductivity also improves while the temperature rises, just like the viscosity. So, the equation we used in section 1.8.2, which is based on Arrhenius model, can also be viable when it comes to conductivities of deep eutectic solvents.

1.9 Applications of DESs[2][3][13]

16 The applications of deep eutectic solvents have drawn more and more attention in industry lately. Due to their various properties that are similar with traditional ionic liquids, and several advantages such as the ease of synthesis, low cost, the green credential, they have a great potential of replacing ionic liquids and even some non- ionic solvents as a new generation of solvent being used in many domains.

Deep eutectic solvents have been used in various parts of industry nowadays. For example, they have been used for metal processing, adsorbing, synthesizing domain, and biotransformations. The section below is going to introduce some of the main applications of DESs.

1.9.1 Gas adsorption[1]

This is one of the most well-known applications of deep eutectic solvents. Like traditional ionic liquids, DESs have a strong capability of dissolving gas like dioxide, which makes them a kind of solvent that has a potential of reducing global warming.

One of the most well known deep eutectic solvent that has been discovered as a good gas adsorbent is composed of choline chloride and urea. This example is discovered by Han et al. They not only discovered the fact about choline chloride/urea DES, but also did some research about the properties and the affecting

factors of its capability of adsorbing CO2. For instance, it is known that the

17 of CO2 is influenced by the content of choline chloride and several change in the environment such as pressure, temperature. Like the eutectic point is reached at

certain ratio of HBD and HBA, the solubility of CO2 will be maximized at a certain ratio of materials. In this case, is 1:2 of choline chloride: urea. Additionally, the ability

of choline chloride/urea DES to dissolve CO2 has a negative correlation with the temperature (the lower the temperature, the higher the solubility), and a positive correlation with pressure (the higher the pressure, the higher the solubility).

More and more kinds of DESs that are formed with different combination of HBD and HBA have been discovered by various researching team or facilities. It is shown that this sort of -like solvents indeed have a large potential in this domain.

Figure 1.8 The correlation between the CO2 adsorption of polyDEM and pressure.

Adapted with permission from reference[1] Macromol. Rapid Commun. 2016, 37,

1135-1142. Copyright (2016) Wiley

1.9.2 Extraction of glycerol in biodiesel[13]

Biodiesel is considered as one sort of green fuel. Normally it is synthesized via a 18 transesterification reaction of vegetable oil with methanol or . During the process, glycerol is a by-product we don’t want that would form inevitably. Unlike biodiesel, the polarity of glycerol is rather high. So generally we take advantage of this property, and remove most of the glycerol through the “decantation” method.

However, this method is not enough, there will still be some glycerol left in the biodiesel, and this is when deep eutectic solvent comes in handy. During the synthesis of deep eutectic solvent, glycerol can play a role as a hydrogen bond donor.

By using this property, the extraction of glycerol was then processed by the following method:

When we want to remove the glycerol completely, we usually add some DESs composed of quaternary ammonium salts and glycerol with certain ratio into the biodiesel. Upon the addition of deep eutectic solvent, the glycerol that exists in the diesel will start to bond with the DES. Eventually, the glycerol in the diesel will bond with the DES we added and form a deep eutectic solvent with a new ratio of HBD and

HBA. After removing the DES from the biodiesel, the purification is completed. Here’s an example of the glycerol content in the DES after added into the biodiesel[13]:

19 Figure 1.9 Glycerol mole fraction in an AcChCl–glycerol mixture in contact with

biodiesel containing glycerol as a function of time. Adapted with permission from reference[2] Chem. Soc. Rev., 2012, 41,7108–7146. Copyright (2012) Royal Society of

Chemistry

As we can see in the figure, at a certain period of time, the glycerol content in the deep eutectic solvent will dramatically increase. This is when most of the glycerol corresponded with the DES, and been removed from the biodiesel.

1.9.3 Ionothermal synthesis

Traditionally, we use “hydrothermal synthesis” method to synthesize single or inorganic materials. In this method, structure-directing agents (SDAs) were added into the solvent (water) during the reaction. The whole system was heated to a high temperature, and the pressure have been controlled in a certain range. Under such unstable and imbalance system, we can synthesize good-quality .

Though this method was quite widely used, another method of synthesizing those

20 materials was designed in 2004. It’s called the “ionothermal synthesis”. During the reaction process of this method, ionic liquids or deep eutectic solvents can be added in. But not only were they been added, they also served as both the reacting solvent and the SDA. The property that deep eutectic solvents are unstable under high temperature makes them a suitable media as hydrothermal synthesis; moreover, under high temperature, the DESs are likely to decompose, and the materials that formed the solvent may breakdown. The material (HBD or HBA) would become a suitable structure-directing agent (SDA). Thus, ionothermal synthesis can be processed with DESs.

1.9.4 Metal processing application

DESs is also viable on various domains of metal processing application, such as metal electropolishing, plating. This is probably due to the properties of DESs (e.g. high solubility of metal salts, the elimination of influence of water)

In traditional metal processing applications, the solvents we use are usually aqueous solvents. Despite the advantages that they have such as good for metal salts, good conductivities, they also have several drawbacks, like toxicity issues, hydrogen embrittlement, electrochemical stability.

Thus, in some instances of metal processing application, deep eutectic solvents started to replace the role of conventional aqueous solvents to be the main liquids

21 we use while dealing with metal application issues, since they have the similar advantages as the aqueous solvents, while in some aspects they can also overcome the obstacles aqueous solvents may come across.

For example, when performing electropolishing, the solvents we use is traditionally aqueous phosphoric and sulfuric acid mixtures along with associated additives. Yet, this sort of is highly toxic, and low current efficiency (due to the gas evolution). However, if we switch the aqueous into deep eutectic solvents, we may get a similar or even better result of electropolishing since they have advantages such as low gas evolution (which will reduce the current efficiency), low toxicity.

2. Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry (DSC) is the most used method, due to its speed, simplicity, and availability. In DSC a sample and a reference are placed together in holders in the instrument. Heaters either ramp the temperature linearly as a function of time or hold the DSC isothermally. The instrument measures the difference in the heat flow between the sample and the reference. The reference sample should have a well-defined heat capacity over the range of temperature to be scanned.

There is a basic principle of this technique is that when the sample undergoes a

22 physical transformation such as , different amount of heat will be needed to maintain the sample and the reference at the same temperature. The increase or decrease of heat flow depends on whether the process is exothermic or endothermic. For endothermic transition, it requires more heat flowing to the sample to increase the temperature at the same rate as the reference. Likewise, less heat is required when it comes to exothermic transition process. By observing the difference of heat flow between the sample and the reference, the DSC instrument can measure the heat absorbed or released during the phase transitions. Besides simple endothermic or exothermic process, DSC can also be used to observe more physical property changes, such as .

With modern DSC instruments, there are software that can help the analysis of the data. Through DSC we can determine properties like the melting points, glass transition temperatures, and heat capacity values.

3. Nuclear Magnetic Resonance Spectroscopy (NMR)

NMR spectroscopy is based on the measurement of absorption of electromagnetic radiation in the radio-frequency region of roughly 4 to 900 MHz. To cause nuclei to develop the energy states required for absorption to occur, it’s necessary to place the analyte in an intense magnetic field (Nuclear magnetic resonance is a physical phenomenon in which nuclei in a strong magnetic field are perturbed by a weak

23 oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at nucleus.)

The intramolecular magnetic field around an atom in a changes the resonance frequency, giving access to details of the electronic structure of a molecule and its individual functional groups. Thus, when it comes to identify organic compounds, NMR spectroscopy is the definitive method.

Preferably, the sample should be dissolved in a solvent (e.g. CDCl3, DMSO.) because NMR analysis of requires a dedicated spinning machine and may not give equally well-resolved spectra.

4. Polarized optical microscopy (POM)

The techniques of polarized optical microscopy include the illumination of the sample with polarized light. Directly transmitted light can be blocked with a polarizer orientated at 90 degrees to the illumination.

Figure 1.10 Material under Figure 1.11 Material under polarized normal microscopy microscopy

24 CHAPTER II

EXPERIMENT I

1. Introduction

One of the advantages of deep eutectic solvents is that they are not hard to make, and the price of the materials are low, non-toxicity. Generally, by simply mixing two materials (HBD and HBA) and heat them up until both materials melts, we can get a homogeneous liquid at certain ratio of material mixture. At that point (the eutectic point), the DES is completed.

In this section, we used several commercial quaternary ammonium salts and diacids as materials to make deep eutectic solvents. The structures of materials we used were pretty simple, the goal of experiment in this section is to try to synthesize a typical deep eutectic solvent and try to illustrate a phase diagram to determine whether it correspond with the figure and phenomena mentioned in other papers.

2. Experimental section

2.1 Materials

Hydrogen bond donor (HBD): Adipic acid

25 Figure 2.1 Structure of adipic acid

Hydrogen bond acceptor (HBA): (i) Tetra-n-butylammonium bromide

Figure 2.2 Structure of Tetra-n-butylammonium bromide

2.2 Preparation of deep eutectic solvent

The preparation of deep eutectic solvents in this section was quite easy: By simply mixing two materials in a 4 mL vial, and heat them up on a hot plate until both materials melts. The amount of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) were calculated at different mole ratio (e.g. 30 mole% of HBD + 70 mole% of HBA, 40 mole% of HBD + 60 mole% of HBA.). In order to make both materials melt, we set the heating temperature to be slightly higher than both materials’ melting points. In this case, it’s 160℃.

By the time all the samples were melted into homogeneous liquids, they were taken out from the hot plate to cool to room temperature. After the temperatures of

26 the vials were low enough, they were checked if any of the combinations remained homogeneous liquid.

2.3 Illustration of phase diagrams

In order to illustrate the phase diagram, we used differential scanning calorimetry (DSC, Pyris DSC8500) as the instrument to characterize the samples.

After running the DSC tests, we are able to determine the melting points of each samples. With those data points, we were supposed to illustrate phase diagrams that are similar to the typical phase diagram of DESs mentioned previously.

Figure 2.3 Photo of Pyris DSC8500 machine

3. Result and discussion

The experiment results of deep eutectic solvents are first visually observed at room temperature. At room temperature, they are supposed to remain transparent liquid with high viscosity.

27 To further confirm their property of melting points, DSC is a very useful tool. In theoretical results, the samples should have melting points that are lower than any of the single materials; At certain ratio, they are supposed to reach a minimum melting point, which is the “eutectic point”.

3.1 Adipic acid + tetra-n-butylammonium bromide:

In this experiment, after the samples were all cooled down to room temperature, we first observed that at the ratio of 40 mole% of adipic acid and 60 mole% of tetrabutylammonium bromide, the product formed a transparent and high viscosity liquid. However, when the samples were put under room temperature longer, all of them crystallized. After running DSC tests, we found that at 43.22℃, we reached the lowest melting point. Thus, the eutectic mixture was formed at 43.22℃, with the ratio of 40 mole% of adipic acid and 60 mole% of tetrabutylammonium bromide.

DSC figure of the samples:

Figure 2.4 DSC figures from 0-50% mole percentage of adipic acid

28 (At first we thought that the product with 40 mole% of HBD and 60 mole% of HBA had a melting point way below room temperature. But it turns out that it eventually crystallized after a very long period of time)

Figure 2.5 DSC figures from 0-50% mole percentage of adipic acid

As you can see from the DSC results, the melting peaks of each combination did follow the trend that were mentioned previously: Started from the eutectic point, the melting points of other combinations of samples had become higher and higher as the difference of mole percentage between the two materials became bigger and bigger.

Then we measured the melting points of all the samples and illustrate a phase diagram. Here’s the result:

29 Table 2.1 Melting points of products with different ratio of materials

Figure 2.6 Phase diagram of DES composed of adipic acid and tetra-n-

butylammonium bromide

The phase diagram we obtained was similar with the typical phase diagram of deep eutectic solvent.

30 4. Conclusion

Through the experiment, we can see that:

(i) The ratio of the acid and quaternary ammonium compounds. It seems that when the mole percentage of both materials are getting closer, the more likely they will form homogeneous liquids, even if they will eventually crystallize, the rate will be slower than other combination that had big difference of mole percentage. In this case, it’s 40 mole% of HBD and 60 mole% of HBA that would form the eutectic solvent.

For this situation, it’s probably due to the number of -OH group on the HBA, which is a diacid.

From Chem. Soc. Rev., 2012, 41,7108–7146:

The figure shows the phase diagram for mixtures of ChCl with five carboxylic acids as a function of the molar composition. For phenylpropionic acid and phenylacetic acid-based DESs, the lowest freezing point was formed at a composition of 67 mol% of acid, which was similar to the case of the ChCl–urea system (Fig. a). This also means that two carboxylic acid molecules are required to complex each chloride anion of choline in order to form the eutectic mixture. In the case of diacids such as oxalic, malonic and succinic acid, the eutectic is formed at 50 mol% of diacid,

31 suggesting a 1 : 1 complex between the HBD and chloride. This is in accordance with the interaction of two carboxylic acid functions per chloride of ChCl (Fig. b).

Figure 2.7 Freezing points of choline chloride with five carboxylic acids. Adapted with permission from reference[2] Chem. Soc. Rev., 2012, 41,7108–7146 Copyright (2012)

Royal Society of Chemistry

Thus, it is speculated that the ratio close to 1:1 of HBD and HBA is because of adipic acid is a “diacid”. With two acid groups in a carboxylic acid molecule, only one acid molecule is required to complex with the halide anion of the quaternary ammonium.

32 CHAPTER III

EXPERIMENT II

1. Introduction

In the last chapter, we successfully reached the eutectic point and illustrated a phase diagram that followed the typical concept of deep eutectic solvents. However, the materials we used in the last chapter, their structures were pretty simple, and the hydrogen bond acceptor (in that case, it was tetra-n-butylammonium bromide) was just monofunctional. This may cause the formation of deep eutectic solvent to be easier.

In this chapter, the hydrogen bond donors we used were still diacids, but we tried to use different kinds of diacids (including adipic acid, succinic acid, and dodecanedioic acid) with different chain lengths, to see if the chain length really had a influence on the synthesis process. Moreover, the hydrogen bond acceptor we used became difunctional, and the structures were more bulky and complicated. The goal of the experiments in this section, is to synthesize deep eutectic solvents, just like the last chapter as well. If the attempt fail, we will still characterize the samples with

33 various instruments, and try to analyze the cause of the failure, to determine whether the structure of HBD and HBA have a influence on the formation of the liquid.

2. Experimental section

2.1 Materials:

Dibromo-p-xylene (CAS#: 623-24-5), tributylamine (CAS#: 102-82-9), trioctylamine

(CAS#: 1116-76-3), adipic acid (CAS#: 124-04-9), dodecanedioic acid (CAS#: 693-23-

2), succinic acid (CAS#: 110-15-6), acetonitrile, methanol

HBD:

(i) adipic acid,

Figure 3.1 Structure of adipic acid

(ii) succinic acid

Figure 3.2 Structure of succinic acid

(iii) dodecanedioic acid

Figure 3.3 Structure of dodecanedioic acid 34 HBA:

(i) n,n'-(benzene-1,4-diyldimethanediyl)bis(n,n-dibutylbutan-1-aminium)

dibromide (Br-Ph-(N(Bu)3)2)

Figure 3.4 Structure of (Br-Ph-(N(Bu)3)2)

(ii) n,n'-(benzene-1,4-diyldimethanediyl)bis(n,n-dioctylbutan-1-aminium)

dibromide (Br-Ph-(N(Oct)3)2)

Figure 3.5 Structure of (Br-Ph-(N(Oct)3)2)

2.2 Synthesis:

2.2.1 Synthesis of n,n'-(benzene-1,4-diyldimethanediyl)bis(n,n-dibutylbutan-1-

aminium) dibromide (Br-Ph-(N(Bu)3)2):

Material: 35 Dibromo-p-xylene, Tributylamine, Acetonitrile

Procedure:

Tributylamine (4g, 5.14mL, 22mmol) in 30 mL of acetonitrile was added dropwise into a stirred solution of dibromo-p-xylene (2.64g, 10mmol) in 10mL of acetonitrile at

55℃. Once the addition completed, the mixture was stirred for 8 hours at 55℃, then allowed to cool to room temperature. After cooling, the acetonitrile was mainly removed on a rotary evaporator, then the product was placed in a vacuum oven and dried at room temperature for 12 hours to remove the rest of acetonitrile completely. The final product after appeared as white powder.

Figure 3.6 Photo of (Br-Ph-(N(Bu)3)2)

36 Figure 3.7 NMR figure of (Br-Ph-(N(Bu)3)2)

2.2.2 Synthesis of n,n'-(benzene-1,4-diyldimethanediyl)bis(n,n-dioctylbutan-1-

aminium) dibromide (Br-Ph-(N(Oct)3)2):

Material:

Dibromo-p-xylene, Trioctylamine, Acetonitrile

Procedure:

Trioctylamine(7.78g, 9.6mL, 22mmol) in 35 mL of acetonitrile was added dropwise into a stirred solution of dibromo-p-xylene(2.64g, 10mmol) in 10mL of acetonitrile at

55℃. Once the addition completed, the mixture was stirred for at least 8 hours at 55·

℃, then allowed to cool to room temperature. After cooling, the acetonitrile was mainly removed on a rotary evaporator, then the product was placed in a vacuum oven and dried at room temperature for 12 hours to remove the rest of acetonitrile 37 completely. The final product after drying appeared as yellow powder.

Figure 3.8 Photo of (Br-Ph-(N(Oct)3)2)

Figure 3.9 NMR figure of (Br-Ph-(N(Oct)3)2)

2.2.3 Preparation of deep eutectic solvents (DESs):

Traditionally, we prepare the DESs by simply mixing two materials (HBD & HBA); 38 however, due to the high melting points of Br-Ph-(N(Bu)3)2 and Br-Ph-(N(Oct)3)2, we have a different method here.

First, we calculate the ratios of mixtures (HBD: various acids, HBA: Br-Ph-(N(Bu)3)2

& Br-Ph-(N(Oct)3)2) based on mole percentages (e.g. 30 mole% of acid+70 mole% of

Br-Ph-(N(Bu)3)2) in the total weight of 500mg, the ratio ranges from 30% of acid to

70% of acid. Second, we dissolve the mixtures into methanol in 20Ml vials, then heat the vials on hot plate at 58℃ for 2.5 hours while stirring.

After heating, the methanol was mainly removed on a rotary evaporator, then the products were placed in a vacuum oven and dried at room temperature for 5 hours to remove the rest of methanol completely. The preparation of deep eutectic solvents (DESs) was then done.

2.3 Characterization:

2.3.1 Polarized optical microscopy (POM)

After the products were completed, they were placed on a glass slide to get the images through the polarized optical microscopy. The microscopy was used to observe the of the products. Not only the initial products, but also those that had been through different time periods, to determine the crystallization conditions.

39 2.3.2 1H NMR:

1H NMR spectroscopy ( 300 spectrometer) was used to determine the

structure of the material (Br-Ph-(N(Bu)3)2, Br-Ph-(N(Oct)3)2, various acids) and the products (HBD+HBA in different mole percentage ratios) Then we compare the results of the materials and the products. Through observing the peaks in the NMR figure, we can infer the bonds between the materials or if there are any new molecules formed in the process of reaction. Additionally, we can find out if there were any common grounds between different ratios of products.

2.3.3 Differential Scanning Calorimetry (DSC):

Differential Scanning Calorimetry (DSC) was used to determine the different traits of the materials and products, including melting points, glass transition temperatures. The instrument measures the differences in the heat flow between the sample and the reference, we can observe the physical transformation such as phase transition. And through analyzing the result figures, we can gather different data points and determine the difference of melting points between each ratio of products, and illustrate a phase diagram of each combinations of HBD and HBA, to see if we can really reach the eutectic point.

Detail of DSC process:

(i) adipic acid + Br-Ph-(N(Bu)3)2

40 (1) equilibrate at 25℃

(2) rise the temperature to 120℃ at the rate of 10℃/min

(3) isothermal for 2 min

(4) cool the temperature to -10℃/min

(5) isothermal for 2 min

(2 cycles, equilibrate at 25℃ after the process is done)

(ii) succinic acid+ Br-Ph-(N(Bu)3)2

(1) equilibrate at 25℃

(2) rise the temperature to 130℃ at the rate of 10℃/min

(3) isothermal for 2 min

(4) cool the temperature to -30℃ at the rate of 10℃/min

(5) isothermal for 2 min

(2 cycles, equilibrate at 25℃ after the process is done)

(iii) dodecanedioic acid + Br-Ph-(N(Bu)3)2

(1) equilibrate at 25℃

(2) rise the temperature to 110℃ at the rate of 10℃/min

(3) isothermal for 2 min

(4) cool the temperature to -10℃ at the rate of 10℃/min

(5) isothermal for 2 min

41 (2 cycles, equilibrate at 25℃ after the process is done)

(iv) adipic acid + Br-Ph-(N(Oct)3)2

(1) equilibrate at 25℃

(2) rise the temperature to 160℃ at the rate of 10℃/min

(3) isothermal for 2 min

(4) cool the temperature to -10℃ at the rate of 10℃/min

(5) isothermal for 2 min

(2 cycles, equilibrate at 25℃ after the process is done)

(v) succinic acid + Br-Ph-(N(Oct)3)2

(1) equilibrate at 25℃

(2) rise the temperature to 130℃ at the rate of 10℃/min

(3) isothermal for 2 min

(4) cool the temperature to -50℃ at the rate of 10℃/min

(5) isothermal for 2 min

(2 cycles, equilibrate at 25℃ after the process is done)

(vi) dodecanedioic acid + Br-Ph-(N(Oct)3)2

(1) equilibrate at 25℃

(2) rise the temperature to 130℃ at the rate of 10℃/min

(3) isothermal for 2 min

42 (4) cool the temperature to -20℃ at the rate of 10℃/min

(5) isothermal for 2 min

(2 cycles, equilibrate at 25℃ after the process is done)

3. Result and discussion

Deep eutectic solvents are generally composed of two materials, which are bonded with each other through hydrogen bonds. The materials are the hydrogen

bond acceptors (HBAs, in this case, (Br-Ph-(N(Bu)3)2), (Br-Ph-(N(Oct)3)2)) and hydrogen bond donors (HBDs, in this case, adipic acid, succinic acid, dodecanedioic acid).

When deep eutectic solvents are formed, they often appear as high viscosity liquids, the HBD and HBA homogenize into one phase at certain ratio, and the melting point of the solvent will reduce to a minimum temperature, that temperature is called the “eutectic point”. The eutectic point is normally a lot lower than the melting points of both materials, which enable the solvent to stay at liquid state at room temperature.

43 Figure 3.10 Schematic representation of a eutectic point of binary eutectic system.

Adapted with permission from reference[3] Chem. Rev. 2014, 114, 11060−11082

Copyright (2014) American Chemical Society

If the product doesn’t satisfy the condition of reaching the eutectic point, the products would normally still remain liquid at high temperature, but starting to crystallize when they gradually cool down to room temperature.

However, in this section, the products didn’t follow the general phenomena that was mentioned above.

3.1 Visual observation

Ideally, the products were supposed to be homogeneous, high viscosity liquids at room temperature. However, in this section, the results didn’t do as expected. Some of the products did appear as liquid state at the first place; but they started to crystallize through time. Others just directly crystallized after the solvent was completely removed.

For combinations that were with (Br-Ph-(N(Bu)3)2), the products crystallized

44 quickly upon the moment the solvent was removed

And for Br-Ph-(N(Oct)3)2, the rate of crystallization was clearly much slower than

those with Br-Ph-(N(Oct)3)2 as material. This is probably due to the carbon length difference on the side chains of the materials. The amount of carbon made it harder

to crystallize compared to the products made by (Br-Ph-(N(Bu)3)2)

Figure 3.11 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) at initial

Figure3.12 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) after 1 hour

Figure 3.13 State of 45 mole% adipic acid and 55 mole% (Br-Ph-(N(Bu)3)2) after 2

hours 45 3.2 Polarized optical microscopy (POM)

Through the microscopy, we could observe the structure of the crystal that formed in the product. Even though we put the sample that was still at liquid state under the microscopy as soon as possible, there was already some small crystal particles inside the liquid droplet, and through time passed, the amount of crystal increased. It showed that the initial products were at a meta-stable state, and had a continuous tendency of crystallizing.

Figure 3.14 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Bu)3)2)

Figure 3.15 POM figure of 60 mole% adipic acid+40 mole% (Br-Ph-(N(Bu)3)2)

46 Figure 3.16 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Oct)3)2)

Figure 3.17 POM figure of 50 mole% adipic acid+50 mole% (Br-Ph-(N(Oct)3)2)

3.3 1H NMR

First of all, these are the NMR figures of the materials:

Figure 3.18 NMR figure of (Br-Ph-(N(Bu)3)2)

47 Figure 3.19 NMR figure of (Br-Ph-(N(Oct)3)2)

Figure 3.20 NMR figure of adipic acid

Figure 3.21 NMR figure of succinic acid

48 Figure 3.22 NMR figure of dodecanedioic acid

Then, it’s the comparison between the materials and some of the products:

Figure 3.23 NMR figure of 40 mole% adipic acid + 60 mole% (Br-Ph-(N(Bu)3)2

Figure 3.24 NMR figure of 50 mole% adipic acid + 50 mole% (Br-Ph-(N(Bu)3)2

49 Figure 3.25 NMR figure of 60 mole% adipic acid + 40 mole% (Br-Ph-(N(Bu)3)2

As you can see, the figures just look like the figures of adipic acid and (Br-Ph-

(N(Bu)3)2) overlap, the peaks in the NMR figures of the products barely have shifting.

Figure 3.26 NMR figure of 40 mole% succinic acid + 60 mole% (Br-Ph-(N(Bu)3)2

50 Figure 3.27 NMR figure of 50 mole% succinic acid + 50 mole% (Br-Ph-(N(Bu)3)2

Figure 3.28 NMR figure of 60 mole% succinic acid + 40 mole% (Br-Ph-(N(Bu)3)2

Figure 3.29 NMR figure of 50 mole% dodecanedioic acid + 50 mole% (Br-Ph-(N(Bu)3)2

51 Figure 3.30 NMR figure of 70 mole% dodecanedioic acid + 30 mole% (Br-Ph-N(Oct)3)2

The situations of other combinations were quite similar (the NMR figures of the products looked like the overlap of HBD and HBA, the shifting of peaks was barely seen). We assume that the interactions between the HBD and HBA were rather weak.

This is probably due to the materials we synthesized ((Br-Ph-(N(Bu)3)2), (Br-Ph-

(N(Oct)3)2): For traditional DESs, the HBD and HBA are mainly bonded by hydrogen bond (the H site of the O-H of the diacids and the lone pair on the N site of the quaternary ammonium salt); however, the materials synthesized in this section doesn’t have a lone pair electrons on the N site, instead, it possess a positive charge.

Thus, there’s no hydrogen bond interaction between the HBDs and HBAs, only the one between the bromide ion (Br-) and the H site of the H site on the acids, which is quite low, we assumed. That made the products couldn’t maintain a steady state as a

52 liquid, but soon to crystallize after synthesis. Another potential reason is probably the nature if the HBA themselves.

Additionally, though we considered there were little interactions between the HBD and HBA, we could still found some small peaks on the NMR figure. This is probably due to two reasons: First is the formation of HBr. There is a possibility that HBr might form during the synthesis process. The way to examine whether there is HBr in the system is by measuring the pH of the products. Additionally, since the synthesis method was quite simple, the purification procedure was lack. Those peaks observed in the NMR figures could probably be impurities, too.

3.4 Differential scanning calorimetry (DSC)

Figure 3.31 DSC figure of adipic acid+(Br-Ph-(N(Bu)3)2) (endo up)

53 Figure 3.32 DSC figure of succinic acid+(Br-Ph-(N(Bu)3)2) (endo down)

Figure 3.33 DSC figure of dodecanedioic acid+(Br-Ph-(N(Bu)3)2) (endo down)

54 Figure 3.34 DSC figure of adipic acid+(Br-Ph-(N(Oct)3)2) (endo up)

Figure 3.35 DSC figure of succinic acid+(Br-Ph-(N(Oct)3)2) (endo down)

55 Figure 3.36 DSC figure of dodecanedioic acid+(Br-Ph-(N(Oct)3)2) (endo down)

The results of the DSC figures are quite uncertain.

For the combinations with (Br-Ph-(N(Bu)3)2), it seemed that the figures of the

products would have similar peaks like (Br-Ph-(N(Bu)3)2): Two major peaks, one around 60℃, and another around 90-100℃.

Additionally, for the first figure, besides the fact that the figures of the results are

similar with the (Br-Ph-(N(Bu)3)2) itself. But started from 50 mole% of adipic acid and

50 mole% of (Br-Ph-(N(Bu)3)2), there was a broad peak appeared around 80-100℃,

and the ratio 70 mole% of adipic acid and 30 mole% of (Br-Ph-(N(Bu)3)2) only had one single peak around 100-110℃. For this result, we assume it’s because the bonding interaction between HBD and HBA was rather weak, thus at the temperature was up to a certain magnitude, the energy it provided caused the two materials to dissociate, and there would have a dissociate peak appear. 56 Here is the XRD figure of 55 mole% of adipic acid and 45 mole% of (Br-Ph-(N(Bu)3)2)

below. In this figure, we can find out that the XRD peaks of the product is quite

similar with (Br-Ph-(N(Bu)3)2), there is only a little different between the two of them.

When the crystallization happened, there is a possibility that the (Br-Ph-(N(Bu)3)2)

played a dominant role in the crystallization that happened in the vial. Thus, the

sample we took for the DSC tests had showed the tendency of showing the results

that were similar with (Br-Ph-(N(Bu)3)2).

Product

Adipic acid

Figure 3.37 XRD figure of the material and the DES product

And for Br-Ph-(N(Oct)3)2, there were no really an obvious tendency or phenomena happened in each sample. I think it’s because the rate of the crystallization were

much slower when it comes to products with Br-Ph-(N(Oct)3)2, when doing the tests, the samples might be in different states (Some in crystal state while others might still be in liquid states) and different states of samples had different properties. 57 4. Conclusion

From the experiments and tests above, we can get several conclusions that have space for discussion:

(i) With the lack of the hydrogen bond site, the materials seem to not have enough bonding strength to keep the DES at steady liquid state. The products stay at a meta- stable state and possess a tendency of keep crystallizing.

(ii) The length of carbon chain on the branches of (Br-Ph-(N(Bu)3)2) and Br-Ph-

(N(Oct)3)2 would likely to affect the rate of crystallization of the products.

(iii) The difunctional groups from the HBDs and HBAs might cause the molecule chain to form while synthesizing the DES. This might cause the decrease of , and thus increase the melting points of the products. So, the melting points of those products to be higher, and harder to form liquids at room temperature.

58 REFERENCES

[1]. Isik M.; Ruiperez F.; Sardon H. Innovative Poly(Ionic Liquid)s by the

Polymerization of Deep Eutectic Monomers Macromol. Rapid Commun. 2016,

37, 1135-1142

[2]. Zhang Q.；Vigier K.D.O.；Royer S. Deep eutectic solvents: syntheses,

properties and applications Chem. Soc. Rev., 2012, 41,7108-7146

[3]. Smith E.L.；Abbott A.P.；Ryder K.S. Deep Eutectic Solvents (DESs) and Their

Applications Chem. Rev. 2014, 114, 11060−11082

[4]. Green B.D.；Badini A.J.；O‘Brien R.A. Liquid–liquid equilibria of binary

mixtures of a lipidic ionic liquid with hydrocarbons Phys. Chem. Chem. Phys.,

2016, 18, 2459—2467

[5]. Abbott A.P.；Boothby D.；Capper G. Deep Eutectic Solvents Formed between

Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids J.

AM. CHEM. SOC. 2004, 126 , 9142-9147

[6]. Nkuku C.A.；LeSuer R.J. Electrochemistry in Deep Eutectic Solvents J. Phys.

Chem. B 2007, 111, 13271-13277

[7]. Zhang L.；Zhang Z.；Shen D. 2‑Propanol Dehydration via Extractive

59 [8]. Using a Renewable Glycerol−Choline Chloride Deep Eutectic

Solvent: Vapor−Liquid Equilibrium J. Chem. Eng. Data 2017, 62, 872−877

[9]. Welton T. Room-Temperature Ionic Liquids. Solvents for Synthesis and

Catalysis Chem. Rev. 1999, 99, 2071−2083

[10]. Kulkarni P.S.；Branco L.C.；Crespo J.G. Comparison of Physicochemical

Properties of New Ionic Liquids Based on Imidazolium, Quaternary

Ammonium, and Guanidinium Cations Chem. Eur. J. 2007, 13, 8478-8488

[11]. Abbott A.P.；Capper G.；Davies D.L. Preparation of novel, moisture-stable,

Lewis-acidic ionic liquids containing quaternary ammonium salts with

functional side chains Chem. Commun., 2001, 2010-2011

[12]. Eike D.M.；Brennecke J.F.；Maginn E.J. Predicting melting points of

quaternary ammonium ionic liquids Green Chemistry, 2003, 5, 323-328

[13]. Weng J.；Wang C.；Li H.；Wang Y. Novel quaternary ammonium ionic

liquids and their use as dual solvent-catalysts in the hydrolytic reaction Green

Chem. , 2006, 8, 96-99

[14]. Florindo C.；Oliveira F.S.；Rebelo L.P.N. Insights into the Synthesis and

Properties of Deep Eutectic Solvents Based on Cholinium Chloride and

Carboxylic Acids ACS Sustainable Chem. Eng. 2014, 2, 2416−2425

[15]. Boger D.V.；Mackay M.E. Continuum and molecular interpretation of ideal

60 elastic fluids Journal of Non-Newtonian Fluid Mechanics, 41 (1991) 133-150

[16]. Angell C.A. Dynamic Processes in Ionic Chem. Rev. 1990, 90 . 523-

542

[17]. Xu W.；Cooper E.I.；Angell C.A. Ionic Liquids: Ion Mobilities, Glass

Temperatures, and Fragilities J. Phys. Chem. B 2003, 107, 6170-6178

[18]. Angell C.A. Liquid Fragility and the Glass Transition in Water and Aqueous

Solutions Chem. Rev. 2002, 102, 2627−2650

[19]. Wang L.M.；Velikov V.；Angell C.A. Direct determination of kinetic fragility

indices of glassforming liquids by differential scanning calorimetry: Kinetic

versus thermodynamic fragilities J. Chem. Phys., Vol. 117, No. 22, 8 December

2002

[20]. Richert R.；Angell C.A. Dynamics of glass-forming liquids. V. On the link

between molecular dynamics and configurational entropy J. Chem. Phys., Vol.

108, No. 21, 1 June 1998

[21]. Marquez A.S.；Guiseppi-Elie A. Role of Fragility in the Formation of Highly

Stable Organic Glasses PRL 113, 045901 (2014)

[22]. Morrison H.; Sun C.; Neervannan S. Characterization of thermal behavior of

deep eutectic solvents and their potential as drug solubilization vehicles

International Journal of Pharmaceutics 378 (2009) 136-139

61 [23]. Meng X.; Ballerat-Busserolles K.; Husson P.; Andanson J. Impact of water on

the melting temperature of urea + choline chloride deep eutectic solvent New

J. Chem., 2016, 40, 4492-4499

[24]. Senkov O.N.; Miracle D.B. A new thermodynamic parameter to predict

formation of solid or intermetallic phases in Journal of

Alloys and Compounds 658 (2016) 603-607

[25]. Chu K.; Yuan C.; Li H.; Yang K.; Wang Y. Pressure-induced amorphization and

crystallization of Choline chloride/Ethylene glycol deep eutectic solvent

Journal of Molecular Liquids 242 (2017) 109-114

[26]. Choudhury A.; Winterton N.; Steiner A. In situ Crystallization of Low-

Melting Ionic Liquids J. AM. CHEM. SOC. 2005, 127, 16792-16793

[27]. Craveiro R.; Aroso I.; Flammia V.; Carvalho T. Properties and thermal

behavior of natural deep eutectic solvents Journal of Molecular Liquids 215

(2016) 534-540

[28]. Chiarella R.; Davey R.; Peterson M. Making Co-Crystal The Utility if Ternary

Phase Diagram Crystal Growth & Design, Vol. 7, No. 7, 2007

[29]. Pethsangave D.; Khose R.; Wadekar P. Deep eutectic solvent functionalized

composite as an extremely high potency flame retardant ACS Appl.

Mater. Interfaces 2017, 9, 35319-35324

62 [30]. Deng G.; Cavicchi K. Tuning the Viscoelastic Properties of Poly(n-butyl

acrylate) Ionomer Networks through the Use of Ion-Pair Comonomers

Macromolecules 2017, 50, 9473-9481

[31]. Vittoria V.; Candia F.; Iannelli P.; Immirzi A. Solvent-induced crystallization

of glassy syndiotactic polystyrene Makromol. Chem., Rapid Commun. 9, 765-

769 (1988)

[32]. Ray B.; Elhasri S.; Thierry A.; Marie P. Solvent-induced crystallization of

syndiotactic polystyrene: thermodynamics and morphology Macromolecules

2002, 35, 9730-9736

[33]. Wei B.; Herlach D.M.; Sommer F. Rapid eutectic growth of undercooled

metallic alloys Journal of letters, 1993

[34]. Karma A. Phase-field model of eutectic growth Phys. Rev. E 49, 2245

[35]. Scott H. Phase relationships in the zirconia-yttria system Journal of Material

Science 10 (1975) 1527-1535

[36]. Ding M.; Xu K.; Jow T. Liquid-solid phase diagrams of binary carbonates for

lithium batteries Journal of The Electrochemical Society, 147 (5) 1688-1694

(2000)

[37]. Henderson D. Thermal analysis of non-isothermal crystallization kinetics in

glass forming liquids Journal of Non-Crystalline Solids 30 (1979) 301-315

63