Knoevenagel reaction promoted by functional ionic liquids with primary and tertiary amines

Figures & data

Scheme 1. Knoevenagel reactions promoted by the functional ionic liquid IL-NH₂.

Table 1. Synthesis of amine ionic liquids.

Table 2. Effect of ionic liquids with different structures on the Knoevenagel reaction^a.

Entry	Ionic liquids	VH2O/mL	Time	Isolated Yield (%)
1	[DABCO-CH2CH2CH2NH2]Br	0	3 h	85
2	[DABCO-CH2CH2CH2NH2]Br	0.5	40 min	94
3	[DABCO-CH2CH2CH2NH2]Br	1	15 min	99
4	[DABCO-CH2CH2CH2NH2]Br	3	30 min	97
5	[DABCO-CH2CH2CH2NH2]Br	9	2 h	96
6	[HMTA-CH2CH2CH2NH2]Br	1	50 min	92
7	[HMTA-CH2CH2OH]Br	1	1 h	90
8	[HMTA-CH2CH3]Br	1	4 h	85
9	[DABCO-CH2CH2OH]Br	1	29 min	92
10	[DABCO-CH2CH2CH2CH3]Br	1	3 h	91
11	[DABCO-CH2CH3]Br	1	3 h	90
12	[DABCO-CH2C6H5]Br	1	3 h	88
13^b	[DABCO-CH2CH2CH2NH2]Br	1	15 min	95
14	No ionic liquid	1	24 h	Trace
15^c	[DABCO-CH2CH2CH2NH2]Br	1	25 min	98
16^d	[DABCO-CH2CH2CH2NH2]Br	1	15 min	99

^aReactions were performed with 4-chlorobenzaldehyde (5 mmol) and ethyl cyanoacetate (5 mmol) in the ionic liquid (3 g) at ambient temperature.

^b Ultrasound irradiation with ultrasonic power 360 W, frequency 40 kHz at 35°C.

^c Refers to ionic liquid (2.5 g, 10 mmol).

^d Refers to ionic liquid (3.5 g, 14 mmol).

Table 3. Knoevenagel reaction accelerated by the composite solvent-catalyst system^a.

Entry	RCHO	Product	Time	mp (°C) (lit. mp)	Yield (%)
1			16 h	188.2–188.8 (187)^47	92
2			25 h	100.2–100.9	98
3			15 h	Oil	86
4 ^b			20 h	198.4–199.5	92
5			24 h	139.4–140.2	95
6			35 min	121.6–122.4 (121.8)^48	98
7			12 h	170.8–171.2(170–171)^49	82
8			24 h	162.5–162.9 (162.5)^48	79
9			5 h	107.8–108.4 (108–109)^50	92
10			50 min	74.0–74.7 (72–74)^51	91
11			5 h	82.1–82.8 (81–82)^51	95
12			11 h	140.5–140.9 (140.5)^48	88
13			10 h	125.1–125.7 (125.3)^48	90
14			12 min	51.2–51.9 (50–52)^49	98
15			15 min	92.6–93.2 (92–94)^52	99
16			8 min	96.8–97.5 (94–96)^51	99
17			18 min	81.5–82.1 (81–82)^53	99
18			10 min	169.8–171.5 (168–171)^53	99
19			10 min	168.6–169.2 (168.7)^48	99
20			18 min	129.7–130.5 (130–131)^51	98
21^b			20 min	200.1–200.5 (199–200)^54	98
22			10 min	80.6–81.2 (79–80)^53	85
23			8 h	180.6–181.2(180.0–181.0)^54	89
24			10 h	186.8–187.6(187.5–188.0)^55	93
25			6 min	161.9–162.7 (162–163)^55	99

^a Reactions were performed with aldehyde (5 mmol) and ethyl cyanoacetate (5 mmol) or malonitrile (5 mmol) in the composite solvent-catalyst system with ionic liquid [DABCO-CH₂CH₂CH₂NH₂]Br (12 mmol, 3 g) and water (1 mL) at ambient temperature.

^b Refers to ethyl cyanoacetate (10 mmol).

Table 4. Reusability of the composite solvent-catalyst.

Run	Time (min)	Isolated yield/%
1	15	98
2	15	99
3	15	98
4	15	98
5	15	97
6	15	98

Table 5. Comparisons of the catalyst [DABCO-CH₂CH₂CH₂NH₂]Br with various homogeneous or heterogeneous catalysts in Knoevenagel condensation of 4-chlorobenzaldehyde with ethyl 2-cyanoacetate.

Entry	Catalyst	Solvent	T (°C)	Time (min)	Yield (%)
1^58	Imidazolium chlorideimmobilized SBA-15	solvent free	120	3(microwave)	80
2^59	Nanocrystalline CexZr1-xO2	C2H5OH	80	60	78
3^60	Mesoporous carbon nitride	Toluene	120	12(microwave)	92.1
4^61	L-Proline	PEG400	r.t.	60	82
5^62	PS-[MeIm]Cl-XAlCl3	C2H5OH	r.t.	36	94
6^63	Ni-nanoparticles	C2H5OH	r.t..	45	95
7^64	[γ-H2GeW10O36]^6-	CH3CN	80	60	97
8^65	PMO-IL-NH2	solvent free	r.t..	100	95
9^66	Ag(5%)@TiO2	EtOH	65	30	95
10^28	[DBU][Lac]	solvent free	r.t..	5	93
11^48	Fe3O4@SiO2@propyl@DBU	H2O + PEG-400	40	15	98
12^67	Fe3O4@SiO2@propyl@DABCO	H2O + PEG-400	60	8	100
13^68	DABCO	[HyEtPy]Cl–H2O	50	10	98
14^68	DABCO	H2O	50	30	46
15	Catalyst in this work	H2O	r.t..	15	99

Note: r.t.: room temperature.

Scheme 2. Proposed reaction mechanism.

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