Synthesis of magnetic ionic liquids and teaching materials: practice in a science fair

1 Introduction

Ionic liquids are in general defined as liquid electrolytes composed entirely of ions. The melting point criterion has been proposed to distinguish between molten salt, In Japan, they have been defined as having a stable ‘liquid phase at room temperature’. ^{1 , 2} On the other hand, Ionic liquids are described as liquid compounds that display ionic-covalent crystalline structures. ^{3 , 4} This definition involves pure inorganic compounds (sodium chloride, melting point, mp 801 °C), organic compounds (tetrabutylphosphonium chloride, mp, 80 °C), or even eutectic mixtures of inorganic salts (such as lithium chloride/potassium chloride, 6/4, mp., 352 °C) or organominerals (triethylammonium chloride/copper chloride, 1/1, mp, 25 °C). Among the various known ionic liquids, those based on quaternary ammonium or phosphonium salts exhibit a relatively wide electrochemically stable window, good electrical conductivity, high ionic mobility, a broad range of room-temperature liquid compositions, negligible vapor pressure, and excellent chemical and thermal stabilities. Ionic liquids can be designed by combining cations and anions.

For example, 1,3-Dimethylimidazolium hexafluorophosphate, in which the substituents on either side of the imidazolium salt are the same, is a solid at room temperature, but 1-Butyl-3-methylimidazolium hexafluorophosphate, in which one of the methyl groups is replaced by a butyl group, shows a liquid state at room temperature. 1-Methyl-3-hexylimidazolium hexafluorophosphate has a melting point of −73.5 °C, which is extremely low, and both show a liquid state at room temperature. ⁵ These properties have been primarily explored for application in electrochemistry technologies and as solvents in electronic absorption spectroscopy for highly charged complex ions with high- or low-oxidation states. These materials have also been used as media for the clean liquid-liquid extraction processes, as recyclable alternatives to aprotic solvent or catalysts for organic and organometallic synthesis, catalytic cracking of polyethylene, and radical polymerization, and as media for analytical and physical chemistry, and some of them possess liquid crystal or lubricant properties.

Many reports have been published on the use of ionic liquids as solvents for transition metal catalytic reactions, and remarkable achievements have been noted. Compounds containing transition metal ions as anions in ionic liquids are expected to exhibit unique properties. It was hypothesized that if a single-phase liquid with magnetic properties could be synthesized, it would exhibit useful properties.

This study focuses on the synthesis of magnetic ionic liquids containing metal salts, which are thought to be capable of synthesizing ferromagnetic materials. For example, when 1 mmol of 1-Butyl-3-methylimidazolium Chloride ([C₄C₁IM][Cl]) and 1 mmol of Iron(III) Chloride Hexahydrate (FeCl₃·6H₂O) were weighed and mixed in equal molar proportions under an argon atmosphere, an endothermic solid phase reaction occurred, producing a dark brown 1-Butyl-3-methylimidazolium Tetrachloroferrate(III) ([C₄C₁IM][FeCl₄]), ⁵ liquid and water. Applications of the magnetic ionic liquids have been receiving growing interest recently, and iron-containing Magnetic Ionic Liquids have been used for extraction of aromatic cluster materials from coal direct liquefaction residues.

In the field of Science Education, it is essential to develop teaching materials that are easy and interesting for learners, especially younger ones. For this reason [C₄C₁IM][FeCl₄], was selected, for the Science Fair described here. These materials are readily available and commercially available with an eye on for future research. In addition, it was considered whether the phenomenon itself has scientific appeal and would interest the children attending the Science Fair. Another consideration was whether the process itself can be carried out smoothly by educators using this as teaching materials in school classes, and whether it can be used in science fairs as an activity that contributes to science education in the community.

2 Research methods

3 Results and discussion

As mentioned in the introduction, ionic liquids have unique physicochemical properties, such as low vapor pressure, high thermal stability, a wide electrochemical window, a broad liquid range, and excellent solvation abilities to dissolve many organic and inorganic compounds. Since they are easily recyclable, ionic liquids have been viewed as one of the key materials to realize Green Chemistry as an environmentally-benign solvent for electrochemical reactions, organic reaction, and even for enzymatic reactions.

The magnetic properties of [C₄C₁IM][FeCl₄] were first reported by Japanese researcher. ^{7 , 8} Since then, [C₄C₁IM][FeCl₄] has been reported to exhibit a high extraction selectivity and distribution coefficient, and to be a promising solvent for the extraction and separation of aromatic and aliphatic hydrocarbons. ⁹ Numerous other useful properties have been recognized. In the early stages of research, as ionic liquids are ‘liquids’, studies focused on their composition and what active species they contain. Anions of magnetic ionic liquids were studied as ionic liquids with Iron salts by Raman Scattering and ab Initio Calculations. ¹⁰ VIS-UV, Raman scattering and ab initio calculations indicate that [FeCl₄]⁻ is the predominant iron-containing species in these liquids. Interestingly, however, other properties of [C₄C₁IM][FeCl₄] as a magnetic ionic liquid had not received attention until then.

[C₄C₁IM][Cl] and 1-Ethyl-3-Butyl-imidazorium Chloride([C₂C₁IM][Cl]) was used to create a magnetic ionic liquid and to compare the thermal stability of ionic liquids and the magnetic ionic liquid. At first, TG/DTA analysis was performed to obtain information on the cationic components [C₄C₁IM][Cl] and [C₂C₁IM][Cl]. TG/DTA thermogravimetric measurements were performed to measure the upper temperature limit of magnetic ionic liquids and to investigate their thermal stability.

The experiment started with a sample of the raw material (10–20 mg). Measurements were performed in the temperature range from room temperature to 550 °C at a rate of 5 °C per minute. For [C₄C₁IM][Cl], weight loss begins at around 250 °C and ends at around 280 °C. For [C₂C₁IM][Cl], weight loss begins at around 250 °C and ends at around 280 °C in the same way. This indicates that both ionic liquids exhibit high thermal stability. TG/DTA of the synthesized magnetic ionic liquids were next performed next. The thermal decomposition of [C₄C₁IM][FeCl₄] used started at around 350 °C for weight loss and ended at around 400 °C for weight loss. This indicates that the thermal stability was further improved compared to the material ionic liquid. Magnetic ionic liquids were synthesized with useful magnetic properties from sulfates and have found that when the anions are hybridized, the magnetic properties improve, but the stability of the magnetic ionic liquid itself decreases. ¹¹ This means that high thermal stability is a characteristic of [FeCl₄]⁻. Information from the thermal analysis obtained by TG/DTA measurements represents a useful property of [C₄C₁IM][FeCl₄].

Researchers prepare [C₄C₁IM][FeCl₄], and conduct experiments under dry conditions, such as under an argon atmosphere. This is due to the fact that both [C₄C₁IM][Cl] and FeCl₃·6H₂O are highly hygroscopic. However, when planning to expand the use of [C₄C₁IM][FeCl₄] as a teaching material for classes or science exhibitions in the future, it is not always possible to adjust the reagents under the same conditions.

In this Science Fair, it was also planned to have the children adjust [C₄C₁IM][FeCl₄] on the spot so that they could observe and experience endothermic solid phase reactions and exothermic solid phase reactions. In such cases, it is possible that the proportions of the raw materials may not be exactly the same in the operations performed by the children. Therefore, the experiment was conducted at room temperature in an environment with not particularly dry conditions, and with varying the proportions of [C₄C₁IM][Cl] and FeCl₃·6H₂O in various ways. For the [FeCl₄]⁻ anion, which is the most common active species attracted to the magnet in the system, it was identified as having a stable layer above 300 °C, as seen when measuring [C₄C₁IM][FeCl₄] by TG/DTA, based on our earlier thermal analysis. In other words, [C₄C₁IM][FeCl₄] is attracted by a magnet at room temperature. Results of magnetic ionic liquid preparation mixed in various proportions with [C₄C₁IM][Cl] FeCl₃·6H₂O are shown in Figure 1. Below wiyh [C₄C₁IM][Cl] FeCl₃–6HO = 3:1, 2:1, 1.2:1, 1:1, 1:1.2 (0.83:1), 1:2 (0.5:1), 1:3 (0.33:1), molar ratios, respectively. The upper transparent part of the separation contains a lot of water produced after synthesis. Figures in parentheses are conversion ratios based on FeCl₃·6H₂O. Compared to the TG/DTA results, [C₄C₁IM][Cl] FeCl₃·6H₂O between 1.2: and 1:1.2, indicating that [C₄C₁IM][FeCl₄] is the appropriate ratio. This is also consistent with the results shown by Raman scattering and ab Initio calculations in previous studies. ¹⁰

Figure 1:

Various conditions of magnetic ionic liquids using Iron(Ⅲ) chloride hexahydrate. [C₄C₁IM][Cl] FeCl₃–6H₂O = 3:1, 2:1, 1.2:1, 1:1, 1:1.2(0.83:1), 1:2(0.5:1), 1:3(0.33:1), molar ratios, respectively. Figures in parentheses are conversion ratios based on FeCl₃–6H₂O.

There have been several reported cases of high school classes focusing on the properties of ionic liquids. ^{12 , 13} In Takamatsu, several experiments on the synthesis of ionic liquids and magnetic ionic liquids were taught by the author as a part of a visiting class in the Japan Science and Technology Agency, Super Science High School project (SSH). ¹⁴ The target audience was 48 high school students in Takamatsu, who were taking several advanced classes at the SSH high school, where textbooks containing magnetic ionic liquids are being used. ¹⁵ First, a synthesis experiment was conducted at the high school since it was found to be safe to conduct the experiment in air. ¹⁶ The contents of the classes were as follows.

Contents of the Super Science High School class

1. Comparison of ionic liquids and conventional solvents

   1. Smell the liquid

   2. Find out if a liquid conducts electricity

   3. Hold a flame close to a liquid

   4. Mix the liquids up

2. Synthesis reaction of ethyl butyrate

3. Synthesis experiment of magnetic ionic liquid

Since 2011, the Science Fair in Takamatsu has been held annually, with the exception of one year when the students were restricted from going outside due to Covid-19. As the inclusion of chemical experiments at previous Science Fairs had been planned only to a limited scale, it was decided to plan, organize, and conduct the Science Fair with the support of the Chemical Society of Japan, where chemical ideas took center stage.

The property of magnetism is one of the wonders of science and fascinates everyone from elementary school students to adults. Therefore, as mentioned earlier, it was planned to make this material available to the general public at these science fairs, with the aim of familiarizing students with science from the early grades of elementary school.

In developing the material for the science fair, various efforts were made to make it more interesting. In addition, it was urgent to develop materials that could convey the idea of chemistry to students, especially in the presence of Covid-19, even if it was implemented as a kit on a micro scale. ¹⁷

The brochure for the implementation of the 2024 event was prepared as follows. It included the following two substrates:

1. butyl-3-methylimidazolium chloride ([C₄C₁IM][Cl], Powder A 0.052 g)

2. Iron(III) chloride hexahydrate (FeCl₃·6H₂O, Powder B 0.077 g)

About the experiment the brochure stated that:

“Ionic liquids are solvents composed of ions only, and can dissolve various other substances. Ionic liquids can add various properties and are attracting attention as a new environmentally friendly material. Let’s play with magnetic ionic liquids designed to be attached to magnets.”

For the children’s parents, points to be careful about when conducting the experiments were described in the following simple language: “If FeCl ₃ ·6H ₂ O gets on clothes, wipe them with vinegar and wash them to remove the color easily. Be careful not to get your hands caught in the neodymium magnets,” Figure 2.

Figure 2:

Experimental outline in the brochure. (A) From the left: water-repellent sheet, powder A, powder B, dropper, neodymium magnets, cotton swab, toothpick; (B) on the left: [C₄C₁IM][Cl], on the right; FeCl₃·6H₂O; (C) magnetic ionic liquid after stirring, the lower layer is placed on the water repellent sheet with a dropper; (D) neodymium magnets in action.

For two days in August 2024 at an exhibition hall near Takamatsu Station in the central part of Takamatsu, the prefectural capital, 17 booths were set up at the Science Fair, with the cooperation of nine sponsors, including participants from overseas, high schools, and corporate booths. In addition to the booth where visitors could experience magnetic ionic liquids, there were 15 other hands-on booths, such as one where visitors could make colorful beads using sodium alginate, and another where children could make toys modeled on the way dandelion fluff flies using straws. There were also two demonstration and observation booths, including one in which visitors could see invisible things using infrared cameras.

In order to improve the content and implementation of future Science Fairs, a questionnaire survey was conducted. The numbers surveyed were 350 in 2024. The top three participating age groups were the lower three grades of elementary school. There were also participants from junior high school. Since there was a larger number of participants and survey responses in 2024, it can be assumed that the survey results were more accurate than previous years.

In terms of where the participants lived, in 2024, 80 % and in 2022, 92 % of the participants were from Takamatsu. This year schools located in the second most populous city in Kagawa prefecture also participated, which may have been one of the reasons for the increased reach to other regions.

In 2021 for the online event, 40 % of the participants were from Takamatsu, the location of the event, with slightly less than 50 % from within Kagawa prefecture outside of Takamatsu. More than 10 % were from prefectures other than Kagawa. In the future, further means of online hybrid participation will be considered.

A questionnaire survey on the level of satisfaction and understanding of the science fair was conducted. The level of satisfaction was rated on a four-point Likert scale: 1, very interesting; 2, interesting; 3, not very interesting; 4, not interesting. The results showed that the face-to-face events in 2024 (1, 75 %, 2, 25 %) and 2023 (1, 86.5 %, 2, 13.5 %) received higher ratings than the hybrid formats in 2022 (1, 52 %, 2, 38 %) and 2021 (1, 65.5 %, 2, 31 %) respectively.

A four-point Likert scale was used to ascertain the participants’ levels of comprehension of the key points of the Science Fair. These were as follows: 1. understood well, 2. understood roughly, 3. didn’t understand much, 4. didn’t understand at all. Results were as follows: 2024 (1.75 % 2.19 %, 3.5 % 4.1 %) and 2023 (1.61 % 2.31), 2022 (1.52 %, 2.38 %, 3.7 %, 4.3 %) and 2021 (1.46 %, 2.43 %, 3.11 %). As can be seen, the years when the event was held as a hybrid event showed similar trends regarding the participants’ satisfaction levels.

The aim of this Science Fair is to inspire children by having them experience the joy of trying various things through hands-on experiments related to chemistry. Another aim is to convey the importance, interest, and wonder of chemistry and chemical technology to young people who will be responsible for Japan in the future. One of the goals of this event was to provide children with opportunities to turn their simple questions and curiosity into inspiration, as well as introducing the importance and wonder of chemistry and chemical technology to adults who are not familiar with chemistry. Furthermore, a special section explaining safety measures was included in the brochure handed out to all participants. Due to Covid-19, many experiments were conducted on a micro-scale, environmentally-friendly, experimental style. Many experiments were carried out at low cost. In addition, the staff, students and faculty members involved in this Science Fair were made up of volunteers who shared the same aspirations. In the future, further improvements will be made to continue contributing to the local community and children together with the parents in the coming years and beyond.