Novel and highly efficient electro-catalytic cycloaddition of CO₂ and epoxides to cyclic carbonates over reusable ionic liquid-based cooperative catalytic system

Figures & data

Scheme 1. Electro-catalytic cycloaddition of CO₂ and epoxides to cyclic carbonates.

Table 1. Screening of supporting ionic liquid electrolytes for the cycloaddition of propylene oxide with CO₂ to produce propylene carbonate.^a

Entry	Ionic liquid electrolyte	Ionic liquid (mL)	Charge (F mol^−1)	Time (h)	Yield (%)^b	TOF (h^−1)
1	[BMIm]Cl	10	4	10	58	173
2	[HOOCMMIm]NTf2	10	3	8	79	410
3	[PrSO3HMIm]Cl	10	4	10	65	206
4	[HOEtMIm]OAc	10	2	5	80	578
5	[APMIm]Br	10	2	3	87	952
6	[APMIm]DCA	10	2	2	94	1285
7	[Bpy]BF4	10	3	8	61	315
8	[C4MPd]PF6	10	2	8	75	379
9	[BMIm]DCA	10	2	8	67	332
10	[HOOCMMIm]DCA	10	2	5	83	596
11	[PrSO3HMIm]DCA	10	2	8	71	365
12	[HOEtMIm]DCA	10	2	5	85	634
13	[Bpy]DCA	10	2	8	63	356
14	[C4MPd]DCA	10	2	8	79	410
15	–	0	3	24	27	–
16	[APMIm]DCA	3	2	6	52	471
17	[APMIm]DCA	6	2	4	74	580
18	[APMIm]DCA	8	2	2	91	1178
19	[APMIm]DCA	12	2	2	94	1205
20	[APMIm]DCA	10	0.5	4	57	572
21	[APMIm]DCA	10	1	3	73	810
22	[APMIm]DCA	10	1.5	2	85	935
23	[APMIm]DCA	10	2.5	2	91	1237

^a The reactions were carried out with propylene oxide (10 mmol), CO₂ (balloon), acetonitrile (15 mL) in a single compartment cell equipped with graphite anode, Ti/TiO₂-CNT-Pt cathode and current density 3.4 mA cm⁻² at 50°C.

^b Isolated yield.

Figure 1. Effect of reaction parameters on the electrocatalytic cycloaddition (a) Effect of electrode material on the cycloaddition (10 mmol propylene oxide, balloon CO₂, 15 mL acetonitrile, 10 mL [APMIm]DCA, graphite anode, current density 3.4 mA cm⁻², 50°C, 2 h), (b) effect of current density on the cycloaddition (10 mmol propylene oxide, balloon CO₂, 15 mL acetonitrile, 10 mL [APMIm]DCA, graphite anode, Ti/TiO₂-CNT-Pt cathode, 50°C, 2 h), (c) effect of reaction temperature on the cycloaddition (10 mmol propylene oxide, balloon CO₂, 15 mL acetonitrile, 10 mL [APMIm]DCA, graphite anode, Ti/TiO₂-CNT-Pt cathode, current density 3.4 mA cm⁻², 2 h), and (d) effect of reaction time on the cycloaddition (10 mmol propylene oxide, balloon CO₂, 15 mL acetonitrile, 10 mL [APMIm]DCA, graphite anode, Ti/TiO₂-CNT-Pt cathode, current density 3.4 mA cm⁻², 50°C).

Figure 2. Recycling stability of the electro-catalytic system (propylene oxide (10 mmol), CO₂ (balloon), acetonitrile (15 mL), recovered supporting ionic liquid electrolyte [APMIm]DCA, used graphite anode and Ti/TiO₂-CNT-Pt cathode in a single compartment cell with current density 3.4 mA cm⁻² at 50°C for 2 h).

Figure 3. SEM images of fresh (a) and six times recycled Ti/TiO₂-CNT-Pt (b).

Figure 4. XRD patterns of fresh (a) and six times recycled Ti/TiO₂-CNT-Pt (b).

Figure 5. EDX analysis of fresh (a) and six times recycled Ti/TiO₂-CNT-Pt (b)

Table 2. Electro-catalytic synthesis of cyclic carbonates from epoxides and CO₂.^a

Entry	Epoxide	Product	Time (h)	Yield (%)^b	Selectivity (%)^c	TOF (h^−1)
1			2	93	98	1210
2			2	94	97.2	1285
3			2	91	96.1	1198
4			1	95	96.8	1416
5			2	91	96.6	1192
6			5	86	96.3	967
7			3	90	97	1053

^a Unless otherwise noted, the reactions were carried out with epoxide (10 mmol), CO₂ (balloon), acetonitrile (15 mL), supporting ionic liquid electrolyte [APMIm]DCA (10 mL) in a single compartment cell equipped with graphite anode, Ti/TiO₂-CNT-Pt cathode and current density 3.4 mA cm⁻² at 50°C.

^b Isolated yield.

^c GC analysis.

Scheme 2. Possible cooperative mechanism for the electro-catalytic cycloaddition of epoxides and CO₂ to cyclic carbonates.