# Synthetic approaches to monocatenar and bolaform choline-based ionic liquids

Mahasoa-Salina Souvenir-Zafindrajaona, Sarah Nadir, Jean-Pierre Mbakidi, Věra Jandová, Mark-Arthur Ndong, Vincent Lequart, Patrick Martin, Magdalena Bendova, Sandrine Bouquillon

► To cite this version:

Mahasoa-Salina Souvenir-Zafindrajaona, Sarah Nadir, Jean-Pierre Mbakidi, Věra Jandová, Mark-Arthur Ndong, et al.. Synthetic approaches to monocatenar and bolaform choline-based ionic liquids. Journal of Molecular Liquids, 2025, 429, pp.127642. 10.1016/j.molliq.2025.127642. hal-05421900

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Submitted on 17 Dec 2025

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# Synthetic approaches to monocatenar and bolaform choline-based ionic liquids

Mahasoa-Salina Souvenir-Zafindrajaona<sup>a,c</sup>, Sarah Nadir<sup>b</sup>, Jean-Pierre Mbakidi<sup>a</sup>, Vêra Jandová<sup>c</sup>, Mark-Arthur Ndong<sup>b</sup>, Vincent Lequart<sup>b,D</sup>, Patrick Martin<sup>b,D</sup>, Magdalena Bendova<sup>c,d,D</sup>, Sandrine Bouquillon<sup>a,*</sup>

## ARTICLE INFO

### Keywords:

Ionic liquids
Choline
Ester
Monocatenar
Bolaform
Levulinate
Lactate
Fatty acid

## ABSTRACT

For more than three decades, ionic liquids (ILs) have already proven themselves as a promising class of materials with widespread applications in catalysis, electrochemistry, and biotechnology. Among the various types, choline-based ionic liquids have attracted considerable attention due to their unique properties and potential applications for use in pharmaceutical and biological systems. The present study addresses two different synthetic approaches used to prepare monocatenar and bolaform choline-based ionic liquids (ChILs), highlighting recent advances and challenges in this field. Nine cholinium based derivatives have been prepared, cholinium lactate and levulinate, three cholinium ester perchlorate, lactate and levulinate and four bolaforms. To obtain these bolaforms, the first approach consists of esterifying choline with an unsaturated fatty acid, followed by a cross-metathesis catalyzed by a Grubbs catalyst; the second one consists of synthesizing the fatty diacid and then esterifying it in the presence of choline. Both approaches have been discussed and preliminary physical properties (viscosities, degradation temperatures) of some of these ChILs are given.

## 1. Introduction

The most common definition of ionic liquids defines them as salts with melting points below 100 °C, very often liquid at room temperature. They consist of an organic cation and an inorganic or organic anion and may be used in numerous application domains [1] as for examples synthesis [2], catalysis [3–5], electrochemistry [6], extraction of bioactive agents [7] and dissolution of biopolymers [8].

Ionic liquids derived from choline (ChILs) recently attracted significant attention because of their unique properties and potential applications in various domains such as pharmaceutical formulations, bioseparations and biocatalysis [9]. Choline is a quaternary ammonium compound, naturally available in many living organisms, where it plays a crucial role in various biological processes [10]. The different anions associated with cholinium cation provide a variety of ChILs that have excellent ionic conductivity, high thermal stability, and tunable physicochemical properties.

Indeed, ChILs have been reported to show high thermal stability, with decomposition temperatures ranging from 200 °C to over 400 °C [11]. Choline chloride (ChCl) presents a decomposition temperature of around 260 °C [12] and the ionic conductivity of choline-based ILs is relatively high, making them suitable for electrochemical applications [13]. Choline-based ILs have also efficient solubilization properties of various organic and inorganic compounds such as choline acetate (ChAc) in cellulose dissolution [14]. In addition, ChILs are generally considered relatively non-toxic towards various microorganisms and cell lines [15], as well as biodegradable, with some studies reporting degradation rates comparable to those of traditional surfactants [16]. Recent works show the importance of these choline-based ILs, as for examples biocompatible choline amino acid ILs (ChAAILs) for biomass processing [17,18] and CO₂ capture [17] with optimization and scale-up, and choline (or methylcholine) cinnamate as new sustainable corrosion inhibitors [19].

The most common method of synthetizing monocatenar ChILs

<footnote><sup>a</sup> Institut de Chimie Moléculaire de Reims UMR CNRS 7312 – Université de Reims Champagne-Ardenne, Boîte n° 44, B.P. 1039, F-51687 Reims, France</footnote>

<footnote><sup>b</sup> Université Artois-UniLaSalle, Unité Transformations & Agroressources, ULR7519, F-62408 Béthune, France</footnote>

<footnote><sup>c</sup> Institute of Chemical Process Fundamentals CAS, v. v. l., Rozvojová 135/1, 165 02 Prague 6 – Lysolaje, Czech Republic</footnote>

<footnote><sup>d</sup> Department of Physical Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 – Dejvice, Czech Republic</footnote>

<footnote>* Corresponding author.
E-mail address: sandrine.bouquillon@univ-reims.fr (S. Bouquillon).</footnote>
involves the alkylation of choline chloride [20], introducing various alkyl chains to the quaternary ammonium center and enabling control over the IL's lipophilicity and biological activity. An alternative approach involves the quaternization of trialkylamines with alkyl halides or tosylates [21], yielding a large panel of varying alkyl chain lengths and substitution patterns.

The development of synthetic routes to monocatenar and bolaform ChILs has facilitated the exploration of their unique properties and potential applications. Continued progress in this area is expected to lead to designing of novel ILs for use in pharmaceutical, biological, and technological systems.

Several ammonium- or phosphonium-based ionic liquids having carboxylates from biosourced acids like L-lactic, L-tartaric, pyruvic, malic, malonic, succinic and osidic acids, but also from L or D-proline or L-hydroxyproline as counter anions, were developed by our group over the past few years. The resulting ionic liquids are not readily biodegradable (36 % as highest biodegradation yield), however, they show lower toxicity towards various organisms than commonly used chlorinated and commercial ILs [22–24]. Other ionic liquids based on betaine [25] or choline [26–28] were also prepared in the recent years. As for choline derivatives, cholinium esters with saturated carbon chains were prepared. The ecotoxicity of these ILs was determined using a haemocyte-based bioassay [25], demonstrating the importance of the nature of both cations and anions in influencing the IL toxicity.

In this present study, we describe the synthesis of bolaform ionic liquids from choline using two different approaches, i.e. esterification/ cross metathesis or cross metathesis/esterification with suitable starting substrates. The originality of our approach lies in functionalizing the OH function of choline rather than quaternizing a tertiary amine to provide an ammonium [20,21]. In previous work, we prepared choline-derived ionic liquids with carbon chains of 6 to 12 carbons whose physical or chemical properties and applications are quite different [26–28]. In this paper, we will describe the synthesis of analogous ionic liquids with terminal C=C double bonds as starting materials for bolaform ionic liquids prepared by cross-metathesis, these bolaforms then being able to behave like micelles in catalysis (work in progress).

The advantages and drawbacks of each sequence will be discussed along with a preliminary physico-chemical characterization of the studied structures. A detailed study of the physico-chemical properties of these ionic liquids will then be reported on in a subsequent paper.

## 2. Experimental section

### 2.1. Chemicals used

Choline, methane sulfonic acid, carboxylic acids (10-undenoic, lactic and levulinic acids), Grubbs II catalyst, potassium lactate 60 % in H₂O and sodium perchlorate were purchased from Sigma Aldrich and used as received (see Table 1).

### 2.2. Physicochemical characterization

An AC 250 Bruker and a Bruker Alpha-T FTIR spectrometer were used for ¹H and IR spectra of liquid and solid compounds at room

<table><caption>**Table 1**

Chemicals used for the synthesis of choline-based ionic liquids.</caption><thead><tr><th>Chemicals</th><th>CAS No.</th><th>purity</th></tr></thead><tbody><tr><td>Choline Chloride</td><td>67-48-1</td><td>≥ 98 %</td></tr><tr><td>Methane sulfonic acid</td><td>75-75-2</td><td>≥ 99.0 %</td></tr><tr><td>10-undenoic acid</td><td>112-38-9</td><td>98 %</td></tr><tr><td>D-L Lactic acid</td><td>50-21-5</td><td>≥ 85 %</td></tr><tr><td>Levulinic acid</td><td>123-76-2</td><td>98 %</td></tr><tr><td>Grubbs II catalyst</td><td>246047-72-3</td><td>≥ 99.5 %</td></tr><tr><td>Potassium L-Lactate 60 % in H<sub>2</sub>O</td><td>85895-78-9</td><td>60 % in H<sub>2</sub>O</td></tr><tr><td>Sodium perchlorate</td><td>7791-07-3</td><td>≥ 98.0 %</td></tr></tbody></table>

temperature, respectively. Elemental analyses (C, H and N) were realized using a Perkin – Elmer 2400C, H, N, S element analyser.

The direct infusion MS analysis was performed by means of a Waters Acquity UPLC system coupled with a Waters SYNAPT G2-Si High Resolution Mass Spectrometry equipped with electrospray ionization (ESI) source (Waters Corp., Manchester, UK). The mobile phase A consisted of water containing 0.1 % formic acid, while acetonitrile constituted the mobile phase B. Mass detection was conducted in a negative ion mode, with the source temperature at 100 °C, capillary voltage and cone voltage were set at 2 KV (3 KV in positive mode) and 40 V. The desolvation gas was optimized to 650 L/h, the cone gas flow of 50 L/h and the scan range from 50 to 1600 m/z. Mass was corrected during acquisition using external reference (Lock-Spray) consisting of a 1 ng/µL solution of leucine encephalin at a flow rate of 5 µL/min, in order to make sure the accuracy and reproducibility during the MS analysis. All data collected were acquired using MassLynx™ (V4.1) software in continuum mode.

Thermal decomposition of the studied ionic liquids was measured using a NETZSCH TG 209 F1 Libra recording microbalances in a stream of inert gas (Ar) at the flow rate 50 mL·min⁻¹. The samples of mass of several milligrams were heated in the oven whose temperature was regulated by programmable digital temperature controller to 600 °C at the rate of 2 °C·min⁻¹. The flow of carrier gas was controlled by electronic mass flowmeters. In addition to the TGA and DTG (first derivative of the TGA) curves, endothermic and exothermic effects determined by means of the calculated DTA signal (c-DTA) can also be obtained.

Melting temperatures were measured for the samples solid or waxy at room temperature using the Optimelt (Stanford Instruments) automated melting point apparatus. The samples were prepared by loading the liquid equivalent of 10 µL of the solid salt sample into glass capillary tubes, which were sealed on one end and open on the other. The temperature of the tubes was ramped from 30 to 140 °C at a ramp rate of 0.5 to 2 °C·min⁻¹.

Viscosity as a function of temperature was measured (in mPa·s) using a Brookfield LV-DVII + PRO viscometer using a CP51 cone spindle. The instrument was connected to a HUBER-ministat circulation-type thermo-regulated water bath. The measurements were carried out between 298.15 and 353.15 K. The repeatability of the viscometer was of 0.20 % with an uncertainty in the viscosity measurements of 1.00 % of the full-scale range, declared by the manufacturer.

Density was measured at 298.15 K and constant atmospheric pressure using an Anton Paar oscillating tube densitometer DSA 5000. The device was calibrated using bi-distilled water and heptane (calibration standards provided by H&D Fitzgerald Ltd). The standards and samples were degassed by sonication prior to measurements. The uncertainty of the device stated by the manufacturer of 0.00001 g·cm⁻³ was confirmed by our previous measurements [29,30] in, however for the very viscous samples studied in this work it was estimated to be of 0.0001 g·cm⁻³. Due to the high hygroscopicity of the studied ILs, densities were measured for samples with defined water contents. Density of the pure ILs was then obtained by extrapolation to zero water mass fraction.

The reactions under microwave conditions were carried out using a single-mode CEM DISCOVERS-CLASS microwave oven.

#### 2.2.1. General synthesis process of cholinium-based ILs (CHILs)

In a 250 mL two-necked flask, the corresponding carboxylic acid (levulinic or lactic, 1 eq., 61.09 mmol) was added dropwise to the cholinium hydroxide solution (1 eq., 46 % in H₂O, 61.09 mmol, 15 mL) and water (20 mL). After 24 h of stirring at room temperature under nitrogen atmosphere, the excess of water was evaporated under reduced pressure at 50 °C. The final product was a light or dark yellow orange oil, respectively, and was dried under vacuum for 48 h at 45 °C.

#### 2.2.1.1. Cholinium lactate 1
<figure><img src="image_4.png" /></figure>

Light yellow orange oil. Quantitative Yield.

IR: $\nu$ (cm$^{-1}$) 3500–2800 (CH$_2$OH, N$^+$(-CH$_3$)$_3$), 1587 (COO$^-$), 1478–1343 (CH$_2$), 1118, 1087 (C-O). $^1$H NMR (500 MHz, DMSO) $\delta$ 3.8 (t, $J$ = 7.0, 2H, H3), 3.54 (t, $J$ = 6.7 Hz, 1H, H2'), 3.43–3.39 (m, 2H, H2), 3.12 (s, 9H, H1), 1.08 (d, $J$ = 6.7 Hz, 3H, H1'). $^{13}$C NMR (126 MHz, DMSO) $\delta$ 177.6 (C3'), 67.4 (C2'), 67.2 (C2), 55.3 (C3), 53.2 (C1), 21.5 (C1'). Elemental Analysis: % Calc. for C$_8$H$_{19}$NO$_4$.1.3 H$_2$O: C 44.35, H 10.05, N 6.46. % Found: C 44.40, H 9.720, N 6.42.

### 2.2.1.2. Cholinium levulinate 2

<figure><img src="image_5.png" /></figure>

Dark yellow orange oil. Quantitative Yield.

IR: $\nu$ (cm$^{-1}$) 3500–2800 (CH$_2$OH, N$^+$(-CH$_3$)$_3$), 1704 (C=O), 1567 (COO$^-$), 1478–1368 (CH$_2$), 1165, 1087, 1057 (C-O). $^1$H NMR (500 MHz, DMSO) $\delta$ 3.82 (t, $J$ = 5.7, 2H, H3), 3.42–3.38 (m, 2H, H2), 3.12 (s, 9H, H1), 2.45 (t, $J$ = 7.0 Hz, 2H, H3'), 2.07 (t, $J$ = 6.9 Hz, 2H, H4'), 2.04 (s, 3H, H1'). $^{13}$C NMR (126 MHz, DMSO) $\delta$ 209.7 (C2'), 175.9 (C5'), 67.8 (C2), 55.7 (C3), 53.5, 53.5, 53.4 (C1), 40.5 (C4'), 32.7 (C3'), 29.9 (C1'). Elemental Analysis: % Calc. for C$_8$H$_{19}$NO$_4$.1.6 H$_2$O: C 48.41, H 9.83, N 5.65. % Found: C 48.24, H 9.70, N 5.74.

### 2.2.2. General synthesis process of cholinium ester-based ILs

#### 2.2.2.1. Cho-C11-Cl 3
In a 500 mL three-necked flask choline (1 eq, 89.53 mmol, 12.5 g) and methane sulfonic acid (2 eq, 179.06 mmol, 11.63 mL) with 10-undecenoic acid (2 eq., 179.06 mmol, 36.2 mL) were placed along with molecular sieves. The reaction medium was then heated to 115 °C under reduced pressure (50–100 mbar) and maintained at these conditions for 19 h, yielding a brown solution. The obtained solution was then cooled to room temperature and filtered to remove the molecular sieves. The compound was used without purification for the second step, assuming that the conversion in the current step is 100 %.

#### 2.2.2.2. Cho-C11-ClO$_4$ 4
A solution of Cho-C11-Cl 3 (in 15 mL of water) obtained in the previous step was introduced into a 250 mL Erlenmeyer flask. An excess of sodium perchlorate monohydrate (4 eq., 358.12 mmol, 51.76 g), previously dissolved in a small amount of water (100 mL), was then added. A white precipitate formed immediately, and the reaction medium was then stirred for 24 h to optimize the anionic metathesis between the chloride and perchlorate ions. After the addition of dichloromethane (50 mL) and washing with water (5 x 100 mL) to remove unreacted choline chloride and excess of sodium perchlorate and methane sulfonic acid, the organic phase was evaporated under reduced pressure. Finally, diethyl ether (4 x 100 mL) was added to the reaction medium to help precipitate the perchlorate salt and to remove the unreacted fatty acid. Finally, after filtration and drying under vacuum, a yellow powder was obtained (24 g, 73 % yield).

<figure><img src="image_6.png" /></figure>

mp: 68.90 °C. IR: $\nu$ (cm$^{-1}$) 2921, 2852 (CH$_2$, N$^+$(-CH$_3$)$_3$), 1744 (COOR), 1480–1450 (-CH$_2$-), 1166 (C-O-C), 1075 (ClO$_4^-$). $^1$H NMR (500 MHz, DMSO) $\delta$ 5.79 (qt, $J$ = 16.9, 1H, H13), 5.03–4.89 (dd, 2H, H14), 4.44 (m, 2H, H3), 3.67–3.61 (m, 2H, H2), 3.11 (s, 9H, H1), 2.33 (t, $J$ = 7.5 Hz, 2H, H5), 2.00 (q, $J$ = 7.1 Hz, 2H, H12), 1.53 (m, 2H, H6), 1.35–1.24 (m, 10H, H7, H8, H9, H10, H11). $^{13}$C NMR (126 MHz, DMSO) $\delta$ 172.3 (C4), 138.8 (C13), 114.65 (C14), 63.8 (C2), 57.6 (C3), 52.9, 52.9, 52.2 (C1), 33.3 (C5), 33.2 (C12), 28.7, 28.7, 28.5, 28.4, 28.2 (C7, C8, C9, C10, C11), 24.2 (C6). Elemental Analysis: % Calc. for C$_{16}$H$_{32}$ClNO$_6$ C 51.96, H 8.97, N 3.79. % Found C 52.07, H 9.06 N 3.74.

#### 2.2.2.3. Cho-C11-Lac 5. 4
(1 eq., 13.54 mmol, 5 g) was dissolved in 100 mL of ethanol in a 250 mL Erlenmeyer flask. An aqueous solution of potassium lactate (60 %) (1 eq., 13.54 mmol, 2.870 g) was added to the mixture that was then stirred at room temperature for 24 h. A white precipitate was obtained and filtered. Finally, after evaporation of the solvents under reduced pressure, a yellow-brown oil was obtained (4.58 g, 94 %).

<figure><img src="image_7.png" /></figure>

IR: $\nu$ (cm$^{-1}$) 3371 (OH), 2924, 2853 (CH$_2$, N$^+$(-CH$_3$)$_3$), 1736 (COO$^-$), 1596 (COO$^-$), 1480–1450 (CH$_2$), 909 (HC=CH$_2$). $^1$H NMR (500 MHz, DMSO): $\delta$ 5.78 (m, 1H, H13), 5.03–4.90 (dd, $J$ = 10.5, 7.4 Hz, 2H, H14), 4.44 (t, $J$ = 4.9 Hz, 2H, H3), 3.71–3.65 (m, 2H, H2), 3.44 (q, $J$ = 6.7 Hz, 1H, H2'), 3.13 (s, 9H, H1), 2.33 (t, $J$ = 7.5 Hz, 2H, H5), 2.04–1.95 (m, 2H, H12), 1.58–1.48 (m, 2H, H6), 1.26 (d, $J$ = 6.2 Hz, 10H, H7, H8, H9, H10, H11), 1.05 (d, $J$ = 6.7 Hz, 3H, H1'). $^{13}$C NMR (126 MHz, DMSO) $\delta$ 177.0 (C3'), 172.8 (C4), 139.3 (C13), 115.1 (C14), 67.4 (C2'), 64.1 (C3), 58.2 (C2), 53.4, 53.3, 53.2 (C1), 33.80 (C6), 33.64 (C12), 29.2, 29.1, 29.0, 28.9, 28.7 (C7, C8, C9, C10, C11), 24.6 (C5), 22.1 (C1'). Elemental Analysis: % Calc. for C$_{19}$H$_{37}$NO$_5$: C 63.48, H 10.37 N 3.90. % Found C 63.72, H 10.82 N 3.46.

#### 2.2.2.4. Cho-C11-Lev 6
Similar procedure as for 5 was used with 4 (1 eq., 13.54 mmol, 5 g) dissolved in 100 mL of ethanol and a solution of potassium levulinate (1 eq., 13.54 mmol, 2.08 g) in ethanol (20 mL). A yellow-brown oil was obtained (5.40 g, > 95 %).
<figure><img src="image_8.png" /></figure>

IR: $\nu$ (cm$^{-1}$) 2925, 2854 (CH$_2$, N$^+$(-CH$_3$)$_3$), 1738 (COO), 1711 (CO), 1580 (COO$^-$), 1480–1450 (CH$_2$), 909 (HC=CH$_2$). $^1$H NMR (500 MHz, DMSO): $\delta$ 5.79 (m, 1H, H13), 4.95 (dd, $J$ = 10.9, 7.3 Hz, 2H, H14), 4.44 (t, $J$ = 4.9, 2.4 Hz, 2H, H3), 3.67 (t, $J$ = 5.2, 4.8 Hz, 2H, H2), 3.13 (s, 9H, H1), 2.47 (t, $J$ = 6.9 Hz, 2H, H3'), 2.33 (t, $J$ = 7.5 Hz, 2H, H5), 2.15 (t, $J$ = 6.9 Hz, 2H, H4'), 2.05 (s, 3H, H1'), 2.03 – 1.97 (m, 2H, H12), 1.55 – 1.51 (m, 2H, H6), 1.37 – 1.20 (m, 10H, H7, H8, H9, H10, H11). $^{13}$C NMR (126 MHz, DMSO): $\delta$ 208.5 (C2'), 172.4 (C4), 174.2 (C5'), 138.8 (C13), 114.6 (C14), 63.7 (C3), 57.7 (C2), 52.9, 52.8, 52.8 (C1), 39.7

IR: $\nu$ (cm$^{-1}$) 2930, 2852 (CH$_2$, N$^+$(-CH$_3$)$_3$), 1743 (COOR), 1588 (CO Lact.), 1485–1450 (–CH$_2$–), 1155 (C=O-C), 950 (C=C E), 614 (C=C Z). $^1$H NMR (500 MHz, DMSO): $\delta$ 5.39 (m, 2H, H13, H14), 4.44 (m, 4H, H3, H24), 3.69 – 3.60 (m, 4H, H2, H25), 3.44 (2H, q, $J$ = 7.5 Hz, H2'), 3.12 (s, 18H, H1, H26), 2.34 (t, $J$ = 7.5 Hz, 4H, H5, H22), 1.95 (m, 4H, H12, H15), 1.52 (t, $J$ = 7.3 Hz, 4H, H6, H21), 1.30 – 1.20 (m, 20H, H7, H8, H9, H10, H11, H16, H17, H18, H19, H20), 1.05 (d, $J$ = 7.5 Hz, 6H, H1'). $^{13}$C NMR (126 MHz, DMSO): $\delta$ 177.2 (C3'), 172.8 (C4, C23), 130.5 – 131.7 (C13, C14), 67.5 (C2'), 64.2 (C3, C24), 58.2 (C2, C25), 53.5, 53.4, 53.3 (C1, C26), 33.6 (C12, C15), 32.4 (C16, C11), 29.5, 29.4, 29.2, 29.0, 28.9 (C6, C7, C8, C9, C10, C17, C18, C19, C20, C21), 22.1 (C1').
Elemental Analysis: % Calc. for C$_{36}$H$_{70}$N$_2$O$_{10}$: C 63.04; H 10.29; N 3.97 %.
Found: C 62.96; H 10.62; N 3.75 %.

2.2.2.6. Synthesis of BChoLev$_2$ 8. Similar procedure as for compound 7 was followed with compound 6 (1 eq. 10.98 mmol, 4.23 g) in 20 mL of anhydrous dichloromethane and Grubbs catalyst II (0.01 eq., 0.11 mmol, 3 x 31.07. mg). Compound 8, a dark yellow viscous liquid, was obtained with 54 % yield (2.2 g).

<figure><img src="image_9.png" /></figure>

(C3'), 33.3 (C5), 33.2 (C12), 31.3 (C4'), 29.8, 28.7, 28.6 (C9, C10, C11), 28.5, 28.4, 28.3 (C6, C7, C8) 24.2 (C1'). Elemental Analysis: % Calc. for C$_{22}$H$_{43}$NO$_5$S: C 54.86, H 9.0, N 2.91 %. Found C 57.23, H 9.18, N 2.99.

2.2.2.5. Synthesis of BChoLac$_2$ 7. In a three-necked flask the compound 5 (1 eq. 8.6 mmol, 3.17 g) was dissolved in 20 mL of anhydrous dichloromethane. The reaction medium was stirred under argon at 45 °C for 30 min. The Grubbs catalyst II was then added three times every 30 min (0.01 eq., 0.06 mmol, 3 x 16.19 mg). After 24 h, the solvent was evaporated under vacuum and the resulting mixture washed with a water-ethanol mixture (50 mL, ratio of H$_2$O/EtOH was 1/8). The aqueous phase was then treated three times with activated carbon. After evaporation of the water, compound 7, a yellow viscous liquid, was dried under vacuum (2.39 g, 79 %).

IR: $\nu$ (cm$^{-1}$) 2932, 2851 (CH$_2$, N$^+$(-CH$_3$)$_3$), 1740 (COOR), 1715 (CH$_3$CO), 1585 (COO$^-$), 1154 (C=O-C), 948 (C=C E), 612 (C=C Z). $^1$H NMR (500 MHz, DMSO): $\delta$ 5.23 (m, 2H, H13, H14), 4.26 (m, 4H, H3, H24), 3.67 (m, 4H, H2, H25), 3.12 (s, 18H, H1, H26), 2.51 (4H, t, $J$ = 7.5 Hz, H4'), 2.31 (t, $J$ = 7.5 Hz, 4H, H5, H22), 2.21 (4H, t, $J$ = 7.5 Hz, H3'), 2.04 (6H, s, H1'), 1.83 (m, 4H, H12, H15), 1.48 (t, $J$ = 7.3 Hz, 4H, H6, H21), 1.27–1.18 (m, 20H, H7, H8, H9, H10, H11, H16, H17, H18, H19, H20). $^{13}$C NMR (126 MHz, DMSO): $\delta$ 207.4 (C2'), 176.6 (C5'), 170.9 (C4, C23), 132.4 – 130.9 (C13, C14), 64.5 (C3, C24), 58.6 (C2, C25), 53.5, 53.4, 53.3 (C1, C26), 45.2 (C4'), 32.6 (C3'), 32.4 (C12, C15), 29.5, 29.4, 29.2, 29.0, 28.2 (C6, C7, C8, C9, C10, C17, C18, C19, C20, C21), 30.0 (C1').
Elemental Analysis: % Calc. for C$_{40}$H$_{74}$N$_2$O$_{10}$: C 64.66; H 10.04; N 3.77 %. Found: C 64.22; H 10.43; N 3.47 %.

<figure><img src="image_10.png" /></figure>
<figure><img src="image_11.png" /></figure>

mp: 137.40 °C. IR: ν (cm⁻¹) 2918, 2849 (CH₂, N⁺-(CH₃)₃), 1727 (COOR), 1470–1450 (–CH₂–), 1155 (C-O-C), 1077 (ClO₄⁻), 952 (C=C E), 622 (C=C Z). ¹H NMR (500 MHz, DMSO): δ 5.35 (m, 2H, *H10*, *H11*), 4.47 – 4.40 (m, 4H, *H3*'), 3.68–3.62 (m, 4H, 2H, *H2*'), 3.11 (s, 18H, *H1*'), 2.33 (t, *J* = 7.5 Hz, 4H, *H2*, *H19*), 1.96 (m, 4H, *H9*, *H12*), 1.54 (t, *J* = 7.3

Hz, 4H, H3, H18), 1.25 (m, 20H, H4, H5, H6, H7, H8, H13, H14, H15, H16, H17). ¹³C NMR (126 MHz, DMSO): δ 172.8 (C1, C20), 130.5 (C10, C11), 64.2 (C3'), 58.1 (C2'), 53.5, 53.4, 53.3 (C1'), 33.8 (C2, C19), 32.4 (C9, C12), 29.5, 29.4, 29.2, 29.0, 28.9 (C3, C4, C5, C6, C7, C14, C15, C16, C17, C18), 24.7 (C8, C13). Elemental Analysis: % Calc. for

<figure><img src="image_12.png" /><figcaption>**Scheme 1.** Synthesis of cholinium lactate and levulinate.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Scheme 2.** Synthesis of monocatenar and bolaform cholinium ester lactate and levulinate.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Scheme 3.** Synthesis of bolaform diacid 9.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>Fig. 1. Influence of the nature of the Grubbs catalyst on the cross metathesis of the 10-undecenoic acid.</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Scheme 4. Synthesis of bolaform cholinium ester lactate and levulinate involving a microwaves step.</figcaption></figure>

C₃₀H₆₀N₂Cl₂O₈ with 1.5 H₂O C 53.4, N 4.19, H 9.41 Found C 53.5, N 3.19, H 8.49. HRMS (ESI + ): m/z [M + H]⁺ calcd for C₃₀H₆₀N₂Cl₂O₈: 647.3705; found: 647.3806.

2.2.2.10. Synthesis of BChoLac₂. A solution of **10** (1 eq, 11.31 mmol, 8 g) in DMSO (20 mL) was added to a solution of potassium lactate 60 %

(1 eq., 11.31 mmol, 2.42 g) in ethanol (80 mL). The mixture was heated to 80 °C to solubilize all compounds and then maintained at this temperature and stirred for 24 h. It was then filtered and the remaining solvents removed under reduced pressure. The residue was washed with diethylether (3 x 50 mL) and dissolved in acetone (50 mL) to precipitate the potassium lactate which was then filtered. The solvents were
<table><caption>**Table 2**
Comparison between esterification/metathesis and metathesis/esterification sequences.</caption><thead><tr><th></th><th>Esterification/metathesis</th><th>Metathesis/esterification</th></tr></thead><tbody><tr><td><u>7</u></td><td>54 %</td><td>60 %</td></tr><tr><td><u>8</u></td><td>34 %</td><td>–</td></tr><tr><td><u>11</u></td><td>66 %</td><td>–</td></tr></tbody></table>

concentrated under reduced pressure and a light yellow viscous oil was obtained (7.50 g, 91 %). The same NMR and elemental analyses were obtained as after following the first “classical” pathway, IR spectrometry confirming the absence of the KClO₄ salt.

2.2.2.11. *Synthesis of BChoLev₂ 8.* Under the same conditions employed for the synthesis of compound **7**, the reaction remained incomplete after 24 h, likely due to the limited solubility of the reagents in the DMSO/ethanol mixture.

### 3. Results and discussion

We first prepared the cholinium-based ionic liquids by an acid-base reaction between the cholinium hydroxide and lactic or levulinic acids with quantitative yields (Scheme 1). This approach is different from the method described in the literature for cholinium lactate. Indeed, Zendebad *et al.* [31] prepared first cholinium hydroxide from choline and potassium hydroxide which then reacted with the lactic acid to furnish the cholinium lactate **1**. The one step methodology was extended to levulinic acid to yield cholinium levulinate **2** quantitatively too. Both ionic liquids are quite hygroscopic and water is detected in elemental analysis even after 48 h drying under vacuum.

As previously mentioned, we had already synthesized ionic liquids from choline with saturated chains [26–28]. We therefore used the same methodology herein to synthesize cholinium esters from fatty alcohols, this time with unsaturation at the end of the chain (Scheme 2). The first step consists in a vacuum esterification step to obtain the cholinium

<table><caption>**Table 3**
Decomposition temperatures determined by TGA analysis and density at 25 °C of the studied ChILs.</caption><thead><tr><th>CHILs</th><th>T<sub>dec</sub> / °C</th><th>T<sub>m</sub> / °C</th><th>ρ / g·cm<sup>-3</sup></th></tr></thead><tbody><tr><td>1</td><td>219.9</td><td>amorphous liquid</td><td>1.1283</td></tr><tr><td>2</td><td>198.7</td><td>amorphous liquid</td><td>1.1563</td></tr><tr><td>4</td><td>251.7</td><td>68.90</td><td>Nd – powder</td></tr><tr><td>5</td><td>198.0</td><td>amorphous liquid</td><td>Nd – viscous oil</td></tr><tr><td>6</td><td>195.3</td><td>amorphous liquid</td><td>Nd – viscous oil</td></tr><tr><td>10</td><td>254.5</td><td>133.19</td><td>Nd- powder</td></tr><tr><td>11</td><td>249.5</td><td>137.30</td><td>Nd – powder</td></tr></tbody></table>

Nd: not determined. Estimated relative uncertainties of measurement $U_r(T_{dec}) = 0.1\%$, $U_r(T_m) = 0.1\%$, $U_r(\rho) = 0.01\%$.

ester with chloride as counterion. This compound was not isolated but reacted consecutively with sodium perchlorate. The cholinium ester with perchlorate as counterion was easier to purify due to its low solubility in water, which dissolves the unreacted alcohol and choline and the excess of sodium perchlorate. A second anionic metathesis with potassium lactate or levulinate led to the cholinium lactate or levulinate ester with an 11-carbon chain including a terminal insaturation. Bolaform ionic liquids (**7** and **8**) are then obtained via a cross-metathesis of the two monocatenar ionic liquids (**5** and **6**). Grubbs I and Grubbs II catalysts were used as catalysts and highest yields were obtained with 0.1 eq. Grubbs II (79 % for compound **7** and 54 % for compound **8** compared to 59 and 45 % respectively with 0.1 eq. of Grubbs I). This observation is fully in accordance with the work of Trular *et al.* [32] on carbene rotamer switching in Grubbs I and II catalysts. No metathesis occurred without ruthenium catalyst.

The second approach involves first the synthesis of the diacid by cross-metathesis (Scheme 3).

Two Grubbs catalysts were used for this reaction, Grubbs I and Grubbs II catalysts, and a kinetic study was also carried out following the conversion determined by ¹H NMR (Fig. 1).

It appears that the cross-metathesis reaction was significantly

<figure><img src="image_17.png" /><figcaption>**Fig. 2.** Schematic view of the synthetic process.</figcaption></figure>
<table><caption>**Table 4**
Viscosity of CHILs **1** and **2** as a function of temperature.</caption><thead><tr><th rowspan="2">CHILs</th><th colspan="7">Viscosity (η/mPa·s)</th></tr><tr><th>25 °C</th><th>35 °C</th><th>45 °C</th><th>55 °C</th><th>65 °C</th><th>75 °C</th><th>80 °C</th></tr></thead><tbody><tr><td><sup>1</sup>/<sub>2</sub></td><td>199</td><td>111.35</td><td>67.745</td><td>45.005</td><td>35.535</td><td>27.005</td><td>25.11</td></tr><tr><td><sup>1</sup>/<sub>2</sub></td><td>79.59</td><td>49.745</td><td>34.545</td><td>25.555</td><td>20.375</td><td>17.530</td><td>16.585</td></tr></tbody></table>

Estimated relative uncertainties of measurement $U_r(η) = 0.2\%$.

<figure><img src="image_18.png" /><figcaption>**Fig. 3.** A summary of the TGA curves for structures **1**, **2**, **4**, **5**, **6**, **10**, and **11**.</figcaption></figure>

improved by using the Grubbs II catalyst. This observation is fully in agreement with previously described works, respectively the work of Paredes-Gil *et al.* which attributed this improved reactivity of Grubbs II to the readily formed ruthenacyclobutane intermediate with Grubbs II due to thermodynamics and dielectric polarizability [33], and the work of Trular *et al.* [32].

The reaction (in a similar ratio of substrates and catalyst) was then carried out through microwave activation [34]. The catalyst was added in 6 equal additions over an hour, the treatment of the reaction mixture remaining unchanged. The yield after purification was 77 % (1 h reaction time) versus 86 % (24 h reaction time), which represents a considerable improvement in the context of sustainable chemistry.

Esterification of the diacid **9** was then conducted with two different equivalents of methane sulfonic acid (Scheme 4). Under classical esterification conditions used previously, compound **10** was obtained with 77 % yield. In the presence of an excess of methane sulfonic acid and after anionic metathesis with sodium perchlorate, a mixed bolaform ionic compound is obtained with two different anions, chloride and perchlorate. This reproducible reaction is probably due to the highly acidic medium created by the excess of methane sulfonic acid, which can disturb the solubility of the ions involved for metathesis. Compound **11** (more hygroscopic than **10**) may be of particular interest because the chemical behavior of perchlorate and chloride in terms of oxidizing

power or suitable metathesis agents are quite different. Classical anionic metathesis applied to compound **10** led to the lactate bolaform ionic compound **7**, but concerning the anionic metathesis with potassium levulinate, compound **8** could not be obtained even after changing some conditions (substrate ratios, concentrations, solvents).

If we compare the two reaction sequences, the esterification/metathesis sequence yields compounds **7**, **8** and **11** in good yields, whilst with the esterification/metathesis sequence, only compound **7** can be obtained in a yield very close to that obtained with the first reaction sequence (see Table 2). The overall reaction scheme is summarized in Fig. 2.

Some preliminary physico-chemical properties were determined, such as the decomposition temperature, melting temperatures where applicable, density at 25 °C and viscosity as a function of temperature for cholinium lactate and levulinate (Tables 3).

The decomposition temperatures of the compounds **1**, **2**, **4**, **5**, **6** and **11** listed in Table 3 were determined by thermogravimetric analysis (see Fig. 3 for an overall representation of the thermograms and Figures SI-1 to **7** for the original thermograms showing TG and DTG curves) are comprised between 195.8 and 281.2 °C, the highest temperatures being related to the perchlorate derivative **4** and the bolaform **11**. This range is consistent with the decomposition temperatures reported in the literature for Parajo *et al.* [35]. As described in the literature, CHILs containing levulinate have a lower decomposition temperature than CHILs containing the same cation with the lactate anion [27]; this phenomenon is due to the hydrogen bonds present between lactate anions, which increase the decomposition temperature. The same applies to the perchlorate anion, which significantly increases the decomposition temperature. In addition, all the studied ionic liquids with the lactate and levulinate anions appear to decompose in one step, whereas two

<figure><img src="image_19.png" /><figcaption>**Fig. 4.** Viscosity of CHILs **1** and **2** correlated with the Vogel-Tamman-Fulcher equation (Eq. (1), dotted and dash-dotted lines).</figcaption></figure>

<table><caption>**Table 5**
Parameters of the Vogel-Tamman-Fulcher equation for CHILs **1** and **2**.</caption><thead><tr><th rowspan="2">CHILs</th><th colspan="3">Parameters of the Vogel-Tamman-Fulcher equation (Eq.1)</th></tr><tr><th>η<sub>0</sub> (mPa·s)</th><th>B (K)</th><th>T<sub>0</sub> (K)</th></tr></thead><tbody><tr><td><sup>1</sup>/<sub>2</sub></td><td>2.42</td><td>272.6</td><td>236.3</td></tr><tr><td><sup>1</sup>/<sub>2</sub></td><td>2.92</td><td>196.0</td><td>238.9</td></tr></tbody></table>
steps are observed for the structures containing the perchlorate anion.

Then, concerning density and viscosity determination, those could only be measured for CHILs 1 and 2, considering that the other CHILs are waxy or even solid compounds. A more detailed study will be published subsequently, in which the present CHILs will be characterized in the presence of various quantities of water; this allowed for the studied ionic liquids to be liquefied.

It appears that the influence of the levulinate anion is similar to that discussed above, as the viscosities of cholinium lactate were found to be significantly lower than those of cholinium levulinate. It is interesting to note that the simple change of anion then not only has a strong impact on the overall viscosity, but also on its temperature dependence. Indeed, the viscosity of cholinium lactate appears to show a much weaker temperature function, whereas the viscosity of cholinium levulinate sharply decreases with the temperature rise. Although the structure of the anions is relatively similar, the bulkier levulinate has three oxygens with free electron pairs available to form hydrogen bonds with the OH group on the cation. Hydrogen bonding, both O···H and C···halogen, has been found to have a significant effect on the viscosity of ionic liquids, this influence being governed by very complex underlying molecular interactions [36,37]. For example, as shown by Ma et al. in [38], where the effect of hydrogen bonding on viscosity was studied for pyridinium ionic liquids in which C···F bonds were formed, and in [39], where O···H bonds were studied in ammonium-based ionic liquids, the strength of the hydrogen bonds, rather than their number, had a significant influence on the ionic liquid viscosity. The cholinium ionic liquids studied here have similar structures to the ammonium based ILs studied by Ma et al. [39]. Therefore, it can be assumed that in the case of the cholinium levulinate, the hydrogen bonds formed were weak enough to allow a lower viscosity of the ionic liquid.

The viscosity data were then correlated with the Vogel-Tamman-Fulcher (VTF) equation [40]

$$ \eta = \eta_0 \exp \left[ \frac{B}{T - T_0} \right], \quad (1) $$

where η₀, B, and T₀ are adjustable parameters, adjusted using a robust regression along a gnostic influence function [29,30,41] and listed in Table 5. The data correlation is then shown in Fig. 4.

Indeed, it has been shown by Seddon et al. [42] that the viscosity of ionic liquids appears to be non-Arrhenian and that the VTF equation provided a suitable description of the data. Along with density and conductivity measurements, viscosity data will enable us to better understand the microscopic structure of the studied ionic liquids at the origin of their bulk physico-chemical properties [40,43]. This aspect of our study will be further explored in our following work.

## 4. Conclusions

In the present work, nine cholinium ionic liquid structures (7 new ones) were synthesized; of these, two are based on cholinium cations, three on cholinium esters, and four bolaform of cholinium esters have been also prepared. For these last compounds, two synthetic approaches were tested. A classical one involving cross-metathesis of unsaturated cholinium esters provided satisfactory results. An alternative method involving an esterification of a bolaform acid, readily obtained by a micro-wave-assisted cross metathesis, was also found to be viable, however, at the level of the anionic metathesis, poor solubility of the reactants and products in the solvents used herein was found to hinder good yields, particularly for the levulinate derivatives. Moreover, by adjusting the ratios of compounds involved in anionic metathesis, a mixed bolaform IL with chloride and perchlorate as counter anions can be obtained if an excess of methane sulfonic acid is used.

The CHILs proposed in this work are currently undergoing a detailed physico-chemical characterization in the mixtures with various water contents; the results of this study will be published shortly. Indeed, these

CHILs are currently being tested as biopolymer solvents, and the influence of water on their physicochemical characteristics is of great interest in understanding the dissolution results already obtained. In a preliminary study of viscosity of the simple CHILs, an interesting influence of the anion on the structure of the studied compounds has been observed, that is worth to be investigated more thoroughly.

## CRediT authorship contribution statement

**Mahasoa-Salina Souvenir-Zafindrajaona:** Methodology, Investigation, Formal analysis. **Sarah Nadir:** Investigation, Formal analysis. **Jean-Pierre Mbakidi:** Supervision, Methodology, Investigation, Formal analysis. **Vêra Jandová:** Validation, Formal analysis. **Mark-Arthur Ndong:** Validation, Supervision, Formal analysis. **Vincent Lequart:** Funding acquisition. **Patrick Martin:** Funding acquisition. **Magdalena Bendova:** Writing – review & editing, Supervision, Funding acquisition, Formal analysis, Conceptualization. **Sandrine Bouquillon:** Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

This work was supported by the URCA and the Barrande Fellowship of the French Government (PhD of M.S.S.Z.), and the FEDER for material funds. S.N. was funded by the BQR of the University of Artois. M.B. gratefully acknowledges funding from the Czech Ministry of Education, Youth and Sports Mobility project No. 8J21FR0027.

## Data availability

Data will be made available on request.

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