2023 Volume 6 Issue 5 (Published 20 August 2024)
INEOS OPEN, 2023, 6 (5), 138–139 Journal of Nesmeyanov Institute of Organoelement Compounds |
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Cadmium Iodide as a Catalyst for the Addition of Carbon Dioxide to Oxiranes
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, str. 1, Moscow, 119334 Russia
Corresponding author: S. E. Lyubimov, e-mail: lssp452@mail.ru
Received 20 February 2024; accepted 30 March 2024
Abstract
The CdI2-catalyzed addition of CO2 to oxiranes is presented. The catalysts are obtained by mixing amines with CdI2. It is found that amines with a large number of aliphatic groups provide the higher conversion; the presence of additional OH and NH groups negatively affects the conversion.
Key words: cadmium iodide, amines, epoxides, CO2 fixation, organic carbonates.
Introduction
Carbon dioxide is the main anthropogenic greenhouse gas produced by the chemical, thermoelectric and steel industries, as well as the transport sector. Worldwide CO2 emissions have caused many environmental problems, such as climate change and global warming, which makes the recycling of carbon dioxide into different compounds for application purposes an urgent task, despite the sufficient inertness of the molecule. One popular group of chemicals that can be produced from CO2 is comprised by organic carbonates. The latter are used as fuel additives, electrolytes for lithium-ion batteries, polar solvents, monomers for the production of polycarbonates and non-isocyanate polyurethanes [1, 2]. Nowadays, transition metal complexes, ionic liquids, as well as non-metallic catalysts such as organic ammonium, imidazolium and phosphonium salts, including those covalently or weakly bound to solid substrates, are used as catalysts for this process [3, 4]. One of the appealing approaches to reduce the cost of this process is the use of inorganic salts as catalysts owing to their widespread availability. However, due to the low solubility of inorganic halides in organic media, the reactions involving them require high temperatures and a long time [5].
Herein, we report on the use of cadmium iodide as a catalyst for the addition of CO2 to oxiranes, leading to organic carbonates, and the methods for the catalyst activation.
Results and discussion
Cadmium iodide is an inorganic compound that features high solubility in water, alcohols and diethyl ether, suggesting its compatibility with organic compounds. However, its application (1 mol %) in the addition of CO2 to propylene oxide (8a, Scheme 1) afforded only low conversion (Table 1, entry 1).
Scheme 1. Addition of CO2 to oxiranes.
Table 1. CdI2-catalyzed (1 mol %) addition of CO2 to oxiranes (56 atm)
Entry
|
Additive
|
Oxirane
|
T, °С
|
Time, h
|
Conversion, %
|
Yield, %
|
1
|
–
|
8a
|
110
|
2
|
26
|
–
|
2
|
1
|
8a
|
110
|
2
|
81
|
–
|
3
|
2
|
8a
|
110
|
2
|
90
|
–
|
4
|
3
|
8a
|
110
|
2
|
60
|
–
|
5
|
4
|
8a
|
110
|
2
|
72
|
–
|
6
|
5
|
8a
|
110
|
2
|
65
|
–
|
7
|
6
|
8a
|
110
|
2
|
88
|
–
|
8
|
7
|
8a
|
110
|
2
|
80
|
–
|
9
|
2
|
8a
|
120
|
2
|
100
|
95
|
10
|
2
|
8b
|
120
|
2
|
88
|
–
|
11
|
2
|
8b
|
120
|
2.5
|
100
|
97
|
12
|
2
|
8c
|
120
|
2
|
100
|
96
|
13
|
2
|
8d
|
120
|
2
|
100
|
96
|
14
|
2
|
8e
|
120
|
2
|
100
|
92
|
15
|
2
|
8f
|
120
|
2
|
100
|
93
|
16
|
2
|
8g
|
120
|
2
|
100
|
95
|
17
|
2
|
8h
|
120
|
2
|
100
|
94
|
18
|
2
|
10
|
120
|
12
|
100
|
96
|
In order to increase the conversion, we decided to add amines (2 mol %) as the ligands for CdI2. It was found that the higher conversions are provided by amines with a large number of aliphatic groups (Table 1, entries 2, 3 and 4, 5). The presence of additional OH and NH groups negatively affects the conversion (Table 1, entries 2–8), which is most likely associated with the competitive coordination with the oxirane oxygen atom. Triethylamine provides the highest performance. For the optimization of the reaction conditions, the temperature was increased from 110 to 120 °C, which led to the quantitative conversion in the case of triethylamine used as an additive (Table 1, entry 9). The reaction of epoxide 8b bearing an ethyl substituent (Scheme 1) required a longer time (Table 1, entries 10, 11). In the case of more polar oxiranes 8c–h, the complete conversion was achieved in 2 h (Table 1, entries 13–18).
The catalytic system based on triethylamine and CdI2 was also tested for the addition of CO2 to bis-oxirane 10. The quantitative conversion of the substrate was achieved in 12 h. It is noteworthy that bicarbonate 11 is used in the production of high-temperature and mechanically stable adhesives and hydrophilizing coatings [6, 7].
Experimental section
The 1H NMR spectra (400.13 MHz) were recorded on a Bruker Avance 400 spectrometer in CDCl3. Amines 1–7 and epoxides 8a–e, 10 were purchased from commercial sources. Epoxides 8f–h were synthesized according to the published procedures [8–10]. The work was performed with CO2 of 99.99% purity using HIP equipment for its handling.
Synthesis of carbonates 9a–h, 11 from epoxides. CdI2 (0.06 mmol) and amine (0.06 or 0.12 mmol) were placed in a 10 mL autoclave. Then the corresponding oxirane (6.00 mmol) was added. CO2 was introduced into the autoclave at room temperature and heated to the required temperature in a thermostat. After the specified time, the autoclave was cooled to 5 °C, CO2 was released, and CDCl3 (2 mL) was added. The resulting mixture was filtered through a thin layer of silica gel to remove the catalyst residues, and the solution obtained was analyzed by NMR spectroscopy. The spectral characteristics of the carbonates were in good agreement with the literature data [8, 10–13].
Conclusions
Hence, we tested a series of amines in combination with CdI2 in the addition of CO2 to oxiranes. It was found that amines with a large number of aliphatic groups provide the higher conversion, while the presence of additional OH and NH groups negatively affects the conversion. In addition, this report is the first example of the cadmium-catalyzed addition of CO2 to oxiranes [14].
Acknowledgements
This work was performed with financial support from the Ministry of Science and Higher Education of the Russian Federation (agreement no. 075-00277-24-00).
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