Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Br?nsted acidic ionic liquid

Article abstract of DOI:10.3762/bjoc.16.34

Raw material from biomass and green preparation processes are the two key features for the development of green products. As a bio-lubricant in metalworking fluids, estolides of ricinoleic acid are considered as the promising substitute to mineral oil wit

Full text of DOI:10.3762/bjoc.16.34

Oligomeric ricinoleic acid preparation promoted by an
efficient and recoverable Brønsted acidic ionic liquid
Fei You1, Xing He1, Song Gao1, Hong-Ru Li*1,2 and Liang-Nian He*1
Full Research Paper
Open Access
Address:
State Key Laboratory and Institute of Elemento-Organic Chemistry,
College of Chemistry, Nankai University, Tianjin 300071, China and
College of Pharmacy, Nankai University, Tianjin 300353, China
Beilstein J. Org. Chem. 2020, 16, 351–361.
doi:10.3762/bjoc.16.34
1
2
Received: 07 January 2020
Accepted: 24 February 2020
Published: 10 March 2020
Email:
Hong-Ru Li* - lihongru@nankai.edu.cn; Liang-Nian He* -
heln@nankai.edu.cn
This article is part of the thematic issue "Green chemistry II".
Guest Editor: L. Vaccaro
*
Corresponding author
Keywords:
© 2020 You et al.; licensee Beilstein-Institut.
License and terms: see end of document.
bio-lubricant; ionic liquids; oligomeric ricinoleic acid; ricinoleic acid;
sustainable catalysis
Abstract
Raw material from biomass and green preparation processes are the two key features for the development of green products. As a
bio-lubricant in metalworking fluids, estolides of ricinoleic acid are considered as the promising substitute to mineral oil with a
favorable viscosity and viscosity index. Thus, an efficient and sustainable synthesis protocol is urgently needed to make the prod-
uct really green. In this work, an environment-friendly Brønsted acidic ionic liquid (IL) 1-butanesulfonic acid
diazabicyclo[5.4.0]undec-7-ene dihydrogen phosphate ([HSO3-BDBU]H2PO4) was developed as the efficient catalyst for the pro-
duction of oligomeric ricinoleic acid from ricinoleic acid under solvent-free conditions. The reaction parameters containing reac-
tion temperature, vacuum degree, amount of catalyst and reaction time were optimized and it was found that the reaction under the
conditions of 190 °C and 50 kPa with 15 wt % of the [HSO3-BDBU]H2PO4 related to ricinoleic acid can afford a qualified product
with an acid value of 51 mg KOH/g (which corresponds to the oligomerization degree of 4) after 6 h. Furthermore, the acid value of
the product can be adjusted by regulating the reaction time, implying this protocol can serve as a versatile method to prepare the
products with different oligomerization degree and different applications. The other merit of this protocol is the facile product sepa-
ration by stratification and decantation ascribed to the immiscibility of the product and catalyst at room temperature. It is also worth
mentioning that the IL catalyst can be used at least for five cycles with high catalytic activity. As a result, the protocol based on the
IL catalyst, i.e. [HSO3-BDBU]H2PO4 shows great potential in industrial production of oligomeric ricinoleic acid from ricinoleic
acid.
Introduction
In recent years, the biomass has attracted much attention due to and utilization of biomass provides an alternative avenue to
its abundance, renewability and potential of conversion to use- liberate us from the reliance on petroleum resource [1]. Nowa-
ful chemicals. It can’t be denied that the diverse transformation days, fuels, fine chemicals and functional molecules/materials
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Beilstein J. Org. Chem. 2020, 16, 351–361.
can be derived from biomass such as lignocellulose and plant efficient, green and recyclable catalyst and design simple oper-
oils [2,3], wherein the plant oils play an important role in the ating procedures for the preparation of estolides oligomeric rici-
polymer industry [4]. Especially, the characteristics of non- noleic acid.
volatility and biodegradability make plant oil the most promis-
ing material to develop functional polymeric materials with su- Ionic liquids (ILs) have been proved to be efficient catalysts in
perior performance [5-7].
various organic syntheses due to the designable structure,
tunable properties as well as superior solubility [26,27].
Castor oil is one kind of nonedible oil and can be extracted Furthermore, the thermal stability and negligible vapor pres-
from the seeds of the castor bean plant. Globally, around one sure of ILs can facilitate the product separation after reaction.
million tons of castor seeds are produced every year and the To the best of our knowledge, the IL 1-butylsulfonic-3-
leading producing areas are India, China, and Brazil [8]. The methylimidazolium tosylate ([HSO3-BMim]TS) can be used as
castor oil has long been used as purgative or laxative to counter catalyst in the synthesis of oligomeric ricinoleic acid, the
constipation and nowadays it is used commercially as a highly estolide with an acid value of 48 ± 2.5 mg KOH/g was ob-
renewable resource for the chemical industry [9,10]. Numerous tained after 14 h [28]. Nevertheless, the product separation and
platform chemicals such as ricinoleic acid and undecylenic acid catalyst reusability have not yet been investigated until now.
can be prepared from castor oil, wherein ricinoleic acid is a
crucial platform chemical for derivation of useful chemicals Based on the fact that Brønsted acids present excellent catalytic
[
11-14].
activity for this intermolecular esterification reaction and
Brønsted acidic ionic liquids have been successfully used as
Ricinoleic acid can be easily prepared by hydrolysis of castor catalyst in organic syntheses [29-31], we designed a series of
oil [15]. The presence of both hydroxy and carboxy groups in Brønsted acidic ionic liquids and applied them as catalysts for
the molecule of ricinoleic acid enables it to undergo intermolec- the preparation of oligomeric ricinoleic acid from ricinoleic
ular esterification, thus resulting in the formation of the acid to develop a facile synthesis and separation protocol. Grati-
oligomeric ricinoleic acid. The oligomeric ricinoleic acid with fyingly, the IL [HSO3-BDBU]H2PO4 showed to be efficient
different acid value (which is an indirect index for oligomeriza- both in synthesis and product separation [32]. Through process
tion degree) has different applications. For example, as an addi- parameter selection, it was found that a product with different
tive in shampoos, the oligomeric ricinoleic acid with an acid acid value can be obtained by changing the reaction time at
value of 60–90 mg KOH/g is required while for cosmetic 190 °C and 50 kPa with 15 wt % IL as catalyst. The viscosity
formulations, an acid value of 20–40 mg KOH/g is suitable [16- characterization showed the product derived from 6 h of reac-
1
9]. The oligomeric ricinoleic acid can also be used as lubri- tion, whose acid value is 51 mg KOH/g and the corresponding
cant for metal cutting oils due to its appropriate viscosity, good average oligomerization degree is 4, meets the requirement of
adsorptivity and film formation ability on metal surfaces. lubricant additive index. Notably, after reaction, the product and
Furthermore, the biodegradability of these estolides in the envi- IL catalyst can be easily separated by phase separation and the
ronment makes them attractive as green products.
recovered catalyst can be used at least for five cycles without
obvious deactivation, which shows tremendous advantage for
In parallel with the increasing demand for high-quality large-scale industrial application. The reaction and separation
oligomeric ricinoleic acid, the synthetic method has kept on procedures are depicted in Scheme 1.
developing. Traditionally, p-toluenesulfonic or sulfuric acid are
used as catalysts for the preparation of oligomeric ricinoleic Results and Discussion
acid. However, the equipment corrosion and the tedious workup Considering protic acids have catalytic effects on the esterifica-
process are inevitable, which reduce the process efficiency. tion reaction, we designed and synthesized a series of ILs con-
Moreover, the byproduct formation and the resulting product taining protic anions as shown in Scheme 2. With the synthe-
coloration reduce the product quality. To address the above sized ILs as catalyst, the ricinoleic acid esterification was per-
issues, the enzyme catalysis is proposed accordingly. Neverthe- formed and the catalytic activity of these functional ILs was
less, the high cost, low efficiency and operational unstability of evaluated with the acid value of the product as it is a conve-
enzymatic reaction make it difficult to industrial production nient index to monitor the degree of oligomerization by
[
20-25]. Very recently, tin(II) 2-ethylhexanoate has been re- reflecting the concentration of carboxy groups in the system,
ported as an efficient catalyst for the synthesis of oligomeric which has been cross verified by HPLC method [19,28].
ricinoleic acid [19]. Unfortunately, the separation of oligomeric
ricinoleic acid and the recovery of the catalyst still encounters The results showed that the protic anion is necessary for the
difficulties. Therefore, it is urgently desirable to develop an intermolecular esterification as no catalytic activity can be ob-
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Beilstein J. Org. Chem. 2020, 16, 351–361.
Scheme 1: [HSO3-BDBU]H2PO4-promoted oligomerization and separation.
Scheme 2: Structures of ILs used in this work.
served for the IL with aprotic anion (Table 1, entries 1 and 2). acid value as catalytic activity index, the ionic liquid 1-butane-
For the ILs containing protic anions, the ILs containing sulfonic acid triethylamine dihydrogen phosphate ([HSO3-
polyprotic anions are more conducive to esterification (Table 1, BNEt3]H2PO4) performed best among the tested ionic liquids in
entries 1–4 vs 5), which may originate from its higher proton this study (Table 1, entry 8). However, the IL [HSO3-
concentration in the reaction system. With H2PO4− as anion, the BDBU]H2PO4 showed a much more attractive feature in prod-
ILs containing different cations were then synthesized and their uct separation as stratification of product and catalyst was ob-
catalytic activity on the esterification reaction was investigated. served in the flask within a few minutes after reaction (Table 1,
The results (Table 1, entries 5–9) revealed that the cation also entry 9). Therefore, the IL [HSO3-BDBU]H2PO4 not only acts
affected the catalytic activity of the IL. Taking the decrease of as an efficient catalyst but also provides a facile protocol for
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Beilstein J. Org. Chem. 2020, 16, 351–361.
Table 1: Screening of ILs in the esterification of ricinoleic acida.
Entry
IL
Acid value (mg KOH/g)
1
2
3
4
5
6
7
8
9
–
153
152
83
90
68
63
53
51
92
[NMP]CF3SO3
[NMP]HSO4
[NMP]PTSA
[NMP]H2PO4
[HSO3-BPy] H2PO4
[HSO3-BMim] H2PO4
[HSO3-BNEt3]H2PO4
[HSO3-BDBU]H2PO4
aReactions were performed with ricinoleic acid (10 g, 30 mmol) and IL (15 wt %).
product and catalyst separation and thus avoids the workup pro- intermolecular dehydration esterification. The reaction tempera-
cedure. In this context, [HSO3-BDBU]H2PO4 was selected as ture, catalyst loading, and vacuum degree on the reaction
the suitable catalyst for further investigations.
outcome were in detail investigated and the acid value of the
product was used to evaluate the reaction results (Table 2). It
Having selected the IL [HSO3-BDBU]H2PO4 as catalyst, the was easily found that a higher temperature was favorable for the
process optimization was performed to further promote the formation of oligomeric ricinoleic acid (Table 2, entries 1–5).
Table 2: Optimization of the key reaction parametersa.
Entryb
IL amountc (wt %)
Temp. (°C)
Vacuum degree (kPa)
Acid value (mg KOH/g)
1
2
3
4
5
6
7
8
9
10
10
10
10
10
0
160
170
180
190
200
190
190
190
190
190
190
190
190
190
50
50
50
50
50
50
50
50
50
0
123
106
92
88
86
148
117
73
69
101
63
5
15
20
15
15
15
15
15
1
1
1
1
1
0
1
2
3
4
10
30
50
70
52
44
43
aStandard reaction conditions: ricinoleic acid (10 g, 30 mmol) and different amount of IL at a variety of temperature and vacuum degree; breaction
time, 2 h (entries 1–9), 8 h (entries 10–14); cbased on ricinoleic acid.
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Beilstein J. Org. Chem. 2020, 16, 351–361.
When the temperature was 190 °C, the acid value dropped to C12-H bond. That is, in ricinoleic acid (l1, Figure 1), the C12 is
8
8 mg KOH/g in 2 h. Further increasing the reaction tempera- attached to the hydroxy group while in the corresponding ester
ture cannot lead to a significant drop of acid value. Thus, product (l2–10, Figure 1), C12 is linked to the ester bond, thereby
90 °C was selected as the suitable reaction temperature. With resulting in a change in the chemical shift of H connected with
1
the optimal reaction temperature, the amount of catalyst was C12. As the chemical shift of H in methyl at 0.87 ppm does not
studied at 190 °C and a vacuum degree of 50 kPa (Table 2, change before and after the reaction, it is used as reference and
entries 6–9). As expected, the introduction of [HSO3- the peak integral ratio of C12-H (An) to methyl-H (Am) in the
BDBU]H2PO4 can improve the intramolecular esterification 1H NMR spectra is used to determine the oligomerization
greatly compared with the scenario without catalyst and the degree. Theoretically, oligomeric ricinoleic acids with different
catalyst loading has a positive effect on the oligomerization oligomerization degree have their characteristic An/Am values
degree. When the amount of [HSO3-BDBU]H2PO4 exceeded as listed in Table 3. For a specific sample, both the peaks for
1
5 wt % relative to ricinoleic acid, the catalytic efficiency was C12-H and for methyl-H were integrated and the ratio of An/Am
almost unchanged. Therefore, the optimum amount of catalyst was calculated. Then the resulting value was compared with the
was determined to be 15 wt % in the following investigation.
theoretical ones to determine the oligomerization degree of the
product. It should be noted that this calculation is based on the
The vacuum degree is another factor to affect the intermolecu- assumption that the oligomerization degree of the product is
lar esterification as different vacuum degree can result in a dif- monodisperse. Actually, the obtained oligomerization degree is
ferent water removal rate, which may lead to a different equilib- the average oligomerization degree. By adopting the index
rium toward estolides product. Five different levels of vacuum An/Am, the relationship of acid value and oligomerization
degrees were applied to the reaction system, the results showed degree can be constructed. According to the 1H NMR results,
the oligomerization degree increased with increasing vacuum the value An/Am increased as the reaction proceeded (Table 3,
degree (Table 2, entries 10–14). A stable acid value was entries 2–10 vs entry 1), which means that the average oligo-
approached when the vacuum degree was higher than 50 kPa. merization degree of oligomeric ricinoleic acid can be adjusted
Consequently, 50 kPa was select as a suitable vacuum degree. by changing the reaction time.
According to the above results, the suitable conditions for the For oligomeric ricinoleic acid, its physicochemical properties
esterification of ricinoleic acid were set at 190 °C under a depend on the oligomerization degree. In order to be used as
vacuum degree of 50 kPa and with 15 wt % [HSO3- lubriant in metal-working fluid, the viscosity and the viscosity
BDBU]H2PO4 as catalyst. Under the selected conditions, the index of oligomeric ricinoleic acid should fall into the accept-
acid value versus reaction time was inspected by sampling able scope according to Hostagliss L4 oil soluble lubricant addi-
every 2 h (Table 3, entries 2–10). Simultaneously, the 1H NMR tive product index. To determine the suitable reaction time and
spectra of the samples in CDCl3 were also examined. In the obtain the qualified product, the viscosity and viscosity index of
1
H NMR study, a peak found at 3.62 ppm gradually disap- samples derived from 4 h, 6 h and 8 h of reaction (i.e. NK-A,
peared and a new peak at 4.88 ppm appeared (Figure 1). This is NK-B and NK-C) were further measured and the results are
associated with the changes of the chemical environment for the compared with the commercial product Hostagliss L4 (Table 4).
Table 3: Acid value and the average oligomerization degree of oligomeric ricinoleic acid versus reaction timea.
Entry
Reaction time
Acid value
(mg KOH/g)
Experimental
Theoretical
An/Am
Average oligomerization
degree
(h)
An/Am
1
2
3
4
5
6
7
8
9
0
2
4
6
8
10
12
14
16
18
162
73
60
51
44
38
32
26
21
17
–
–
–
2
3
4
5
6
7
8
9
0.1682
0.2219
0.2530
0.2680
0.2781
0.2861
0.2915
0.2963
0.2999
0.1670
0.2220
0.2500
0.2670
0.2780
0.2857
0.2917
0.2963
0.3000
1
0
10
aThe ricinoleic acid with an acid value of 162 mg KOH/g was used as raw material and interval sampling was performed every 2 h.
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Beilstein J. Org. Chem. 2020, 16, 351–361.
Figure 1: Monitoring oligomerization process by 1H NMR (400 MHz, CDCl3).
Table 4: Physicochemical properties of oligomeric ricinoleic acid compared to Hostagliss L4.
Viscosity (mm2/s)
Entry
Sample
Acid value (mg KOH/g)
Viscosity index
4
0 °C
100 °C
1
2
3
4
Hostagliss L4
NK-A
52
60
51
44
400
373
408
514
45
39
46
53
169
154
171
167
NK-B
NK-C
As the results listed, NK-B meets the specifications of lubricant, thus renders an easy catalyst recyclability and product separa-
which indicated that 6 h of reaction under the catalysis of tion. After decanting the upper product and washing the
[
HSO3-BDBU]H2PO4 can afford the standard-compliant bio- remaining IL with a small amount of dichloromethane, the
lubricant oligomeric ricinoleic acid.
weight of [HSO3-BDBU]H2PO4 was examined and then the
fresh ricinoleic acid was added for the next cycle synthesis of
oligomeric ricinoleic acid. The IL catalyst was used in five
Reusability of [HSO3-BDBU]H2PO4
As the IL catalyst [HSO3-BDBU]H2PO4 is immiscible with the cycles of reaction and the resulting acid value of the product in
product at room temperature, stratification occurs after reaction, each cycle was presented in Figure 2 along with the weight of
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Beilstein J. Org. Chem. 2020, 16, 351–361.
Figure 2: Reusability of the IL catalyst. Reaction conditions: 10 g (30 mmol) ricinoleic acid, 190 °C, 6 h, 50 kPa.
catalyst. It can be seen that [HSO3-BDBU]H2PO4 can be [HSO3-BDBU]H2PO4 was examined after five cycles of reac-
utilized repeatedly for at least five times and only a slight de- tion and the results were presented in Figure 3. It can be seen
crease in catalytic activity was observed, which may be due to that the IL catalyst was stable during the reaction as the spec-
the weight loss of the recovered catalyst. To check the stability trum remained basically unchanged compared with the fresh
of the [HSO3-BDBU]H2PO4 during reusability, the 1H NMR of catalyst.
Figure 3: 1H NMR (400 MHz, DMSO-d6) spectra of [HSO3-BDBU]H2PO4: a) Fresh one; b) used one after five cycles.
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Beilstein J. Org. Chem. 2020, 16, 351–361.
Proposed mechanism
hydroxy groups in the dimeric ricinoleic acid may further
According to our experimental results, the protic acid is crucial undergo esterification, providing the oligomeric ricinoleic acid
for the reaction. Therefore, it is inferred that the reaction under- with different oligomerization degree.
goes proton-promoted intermolecular esterification and the
reaction mechanism with catalyst [HSO3-BDBU]H2PO4 is Conclusion
depicted in Scheme 3. Firstly, the Brønsted acidic IL [HSO3- To conclude, a highly efficient Brønsted acidic IL catalyst
BDBU]H2PO4 activates the carbonyl group of ricinoleic acid, [HSO3-BDBU]H2PO4 was developed for the esterification of
leading to the generation of intermediate A. Concurrently, the ricinoleic acid. The reaction performed well under solvent-free
hydroxy group in another ricinoleic acid molecule may be acti- conditions, the qualified biolubricant oligomeric ricinoleic acid
vated by the cation of IL and attacks the intermediate A (step I), can be prepared at 190 ºC and under vacuum degree of 50 kPa
generating a tetrahedral intermediate B. Finally, dehydration with 15 wt % IL as catalyst in 6 h. Both the acid value and aver-
and deprotonation of the tetrahedral intermediate occurs age oligomerization degree of the product were determined and
(
step II), forming dimeric ricinoleic acid C. The carboxyl and it was found the acid value was 51 mg KOH/g and the average
Scheme 3: Proposed mechanism for [HSO3-BDBU]H2PO4 catalyzed oligomeric ricinoleic acid synthesis.
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Beilstein J. Org. Chem. 2020, 16, 351–361.
oligomerization degree was 4. The reaction has excellent selec- added into a 100 mL glass flask equipped with magnetic stirrer,
tivity and no other byproducts were detected except water. a reflux condenser and connected with vacuum line. Then,
More remarkably, a simple stratifying at room temperature will under a stirrer rate of 500 r/min, the temperature was increased
cause the separation of catalyst and product, which means the to 190 °C to promote the esterification reaction. Simultaneous-
additional solvent extraction or distillation separation em- ly, the reaction run at 50 kPa to remove the generated water.
ployed in the traditional IL catalysis was unnecessary in this After 2 h of reaction, the reaction mixture was cooled to room
system. Besides, the catalyst can be reused at least for five temperature for stratifying. The supernatant was oligomeric
cycles without significant activity lost. Therefore, this protocol ricinoleic acid and it could be decanted directly for further treat-
employing the Brønsted acidic ionic liquid as catalyst repre- ment and acid value analysis. The IL catalyst deposited in the
sents a green synthesis method for oligomeric ricinoleic acid lower layer can be washed with a small amount of dichloro-
and can be run in environmentally manner. It is a promising methane to remove the residual oligoester. After that, the fresh
candidate for the commercial production of oligomeric rici- ricinoleic acid was added for the second run reaction and the
noleic acid from ricinoleic acid.
recovered catalyst can be used repeatedly.
Experimental
Preparation procedure of [HSO3-
BDBU]H2PO4
Product characterization
The oligomeric ricinoleic acid is a yellow oily liquid, and all
experiments have yields greater than 90%, which are deter-
To prepare the IL [HSO3-BDBU]H2PO4, 0.1 mol (13.6 g) 1,4- mined by weighing. The spectral results identified the product.
butane sultone was mixed with 0.1 mol (15.2 g) 1,8-diazobi- 1H NMR (400 MHz, CDCl3) δ 0.85–0.88 (t, J = 3.9 Hz, 3H),
cyclo[5,4,0]undec-7-ene (DBU) in a flask containing 50 mL of 1.26–1.29 (m, 16H), 1.51–1.60 (m, 4H), 2.00–2.01 (m, 2H),
acetonitrile. After 24 h reflux at 80 °C, the reaction mixture was 2.25–2.26 (m, 4H), 4.86–4.89 (m, 1H), 5.30–5.46 (m, 2H) ppm;
cooled to room temperature. Then 30 mL diethyl ether was 13C NMR (100 MHz, CDCl3) δ 14.08, 22.58, 25.11, 25.35,
added to the reaction mixture to precipitate the product. After 27.20–27.35, 29.03–29.71, 31.75, 31.98, 33.62, 34.65, 73.69,
that, the precipitate was collected by filtration and washed twice 124.30, 132.51, 173.58 ppm; FTIR (KBr) νmax/cm−1: 3416.44,
with diethyl ether. The resulting light yellow precipitate was 3010.55, 2927.89, 2855.81, 1733.38, 1711.66, 1464.22,
then dried in vacuum at 60 ºC for 4 h. Afterwards, the aqueous 1245.41, 1183.74, 725.11; ESIMS (+) m/z: 579.3, 876.6,
solution containing a stoichiometric amount of phosphoric acid 1139.7, 1437.8, 1716.9, 1997.1.
was added dropwise to 50 mL CH2Cl2 containing 0.05 mol
(
14.4 g) [HSO3-BDBU] and stirred at 60 °C for 4 h, forming a Acid value determination
viscous liquid on the surface of CH2Cl2 which can be easily The acid value of product was determined using a modified
separated by centrifugation. Then the viscous liquid was ASTM D664 method [33], in which about 1 g sample was
washed twice with CH2Cl2 and dried at 100 ºC for 12 h, obtain- dissolved in 30 mL CH2Cl2 and the resulting solution was
ing 18.6 g yellow viscous liquid with the yield of 96%. The re- titrated against standard 0.1 N isopropanol KOH. Acid value
sulting compound was identified to be IL [HSO3- (mg KOH/g sample) was then calculated as follows:
BDBU]H2PO4. 1H NMR (400 MHz, DMSO-d6) δ 1.62–1.67
(
2
(
2
m, 10H), 1.92–1.98 (m, 2H), 2.41–2.45 (t, J = 6.8 Hz, 2H),
.85–2.88 (t, J = 4.8, 2H), 3.42–3.62 (m, 8H) ppm; 13C NMR
100 MHz, DMSO-d6) δ 19.65, 22.13, 22.88, 25.55, 27.12,
7.22, 27.90, 46.58, 48.52, 50.65, 52.92, 53.98, 165.98 ppm; where V (mL) and C (mol/L) are the consumed volume and
FTIR (KBr) νmax/cm−1: 3317.18, 2939.11, 2867.62, 1621.52, concentration of KOH solution, respectively, W (g) is the
527.51, 1452.10, 1328.75, 1201.00, 998.74, 726.90, 600.28; weight of the sample.
ESIMS (+) m/z: 100.1, 102.1, 153.2, 289.3, 390.1.
1
To exclude the presence of IL in supernatant and ensure the
For the preparation of other ILs in this paper and for full experi- reliability of acid value in oligomerization degree determina-
mental data see Supporting Information File 1.
tion, additional treatment was performed for the supernatant
before acid value determination. That is, the supernatant was
diluted with dichloromethane, and the putative IL in the sample
was extracted three times with distilled water. Then the
Catalytic dehydration esterification of
ricinoleic acid and catalyst recycling
The dehydration esterification of ricinoleic acid was investigat- remaining organic phase was dried with Na2SO4 for 24 h fol-
ed using ILs as catalyst. In a typical run, 10 g (30 mmol) rici- lowed by filtration. After that, the filtrate was collected and the
noleic acid and 1 g (2.6 mmol) [HSO3-BDBU]H2PO4 were dichloromethane solvent was removed by vacuum evaporation
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Beilstein J. Org. Chem. 2020, 16, 351–361.
6
.
Biermann, U.; Friedt, W.; Lang, S.; Lühs, W.; Machmüller, G.;
Metzger, J. O.; Rüsch gen. Klaas, M.; Schäfer, H. J.; Schneider, M. P.
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doi:10.1002/1521-3773(20000703)39:13<2206::aid-anie2206>3.0.co;2-
p
to obtain oligomeric ricinoleic acid for acid value measurement
Table 5, entries 1, 3 and 5). On the other hand, the acid value
of supernatant without any treatment was also determined for
comparison (Table 5, entries 2, 4 and 6). The acid values of the
two treatments were identical, indicating that IL settled well
after the reaction and was absent in the product.
(
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Table 5: Acid value measurement results of two different treatments
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Entrya
Reaction time
Acid value
(mg KOH/g)
(h)
1
2
3
4
5
6
1
1
2
2
4
4
108
108
74
73
60
4.Kim, H. T.; Baritugo, K.-A.; Oh, Y. H.; Hyun, S. M.; Khang, T. U.;
Kang, K. H.; Jung, S. H.; Song, B. K.; Park, K.; Kim, I.-K.; Lee, M. O.;
Kam, Y.; Hwang, Y. T.; Park, S. J.; Joo, J. C.
60
aReaction conditions: 10 g (30 mmol) ricinoleic acid, 1 g (2.6 mmol)
[HSO3-BDBU]H2PO4, 190 °C, 50 kPa.
ACS Sustainable Chem. Eng. 2018, 6, 5296–5305.
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1
1
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Experimental part and spectra of synthesized compounds.
1
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[
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1
2
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Funding
We thank the National Natural Science Foundation of China
(
21975135), Tianjin Nankai University Castor Engineering
26, 155–158. doi:10.1016/j.bej.2005.04.012
Science and Technology Co., Ltd. and Inner Mongolia Weiyu
Biotech Co., Ltd. for financial support.
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Murcia, M. D. Biochem. Eng. J. 2008, 39, 450–456.
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ORCID® iDs
Hong-Ru Li - https://orcid.org/0000-0002-4916-2815
Liang-Nian He - https://orcid.org/0000-0002-6067-5937
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