One-pot, three-component Mannich-type reaction
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aldehydes bearing an electron-withdrawing group were
favorable for the Mannich-type reaction compared with
those carrying electron-donating substituents, and anilines
with electron-donating groups are beneficial for the
reaction.
Table 1 Effect of the [DDPA][HSO4]/solvent system on the Mannich-
type reaction
Entry
Catalyst/solvent
Isolated yield (%)
1
2
3
4
5
6
7
8
[DDPA][HSO4]/H2O
78
87
81
82
65
64
60
62
[DDPA][HSO4]/C2H5OH
[DDPA][HSO4]/CH3OH
[DDPA][HSO4]/CH3CN
[DDPA][HSO4]/CH2Cl2
[DDPA][HSO4]/CHCl3
[DDPA][HSO4]/C6H5CH3
[DDPA][HSO4]/None
The recycling performance of [DDPA][HSO4] in the
same model Mannich-type reaction was also investigated.
After the reaction, the products were isolated from the
catalytic system by filtration. The filtrate (ethanol media
containing the catalyst) was reused in the next run without
further purification. As shown in Fig. 1, the catalyst could
be reused at least six times without appreciable decrease in
yield and reaction rate.
Reaction conditions: 10 mmol benzaldehyde, 10 mmol aniline,
10 mmol cyclohexanone, 1 mmol [DDPA][HSO4], r.t., 6 h
In summary, it was demonstrated that the readily
available, functionalized ionic liquid behaved as a recy-
clable catalyst for the three-component Mannich-type
reaction at room temperature, offering a procedure with
generality and which is environmentally benign, and has
the practical convenience of easy product separation from
the reaction system.
Table 2 Effect of amount of [DDPA][HSO4] on Mannich-type
reaction
Entry
Catalyst (mol%)
Reaction time (h)
Isolated yield (%)
1
2
3
4
5
6
7
8
None
2
36
6
0
59
62
74
87
87
68
87
5
6
8
6
Experimental
10
20
10
10
6
6
Melting points were determined by use of an X6-Data
microscope apparatus. 1H NMR spectra were recorded on a
Bruker DRX300 (300 MHz). Mass spectra were obtained
with an automated Finnigan TSQ Quantum Ultra AM
(Thermal) LC–MS spectrometer. All chemicals (AR grade)
were commercially available and used without further
purification.
3
10
Reaction conditions: 10 mmol benzaldehyde, 10 mmol aniline,
10 mmol cyclohexanone, and 6 cm3 C2H5OH, r.t.
the model reaction to screen the effect of the amounts of
[DDPA][HSO4] on the Mannich-type reaction (Table 2). The
results showed thatnoMannich base could be detected when a
mixture of benzaldehyde, cyclohexanone, and aniline was
stirred for 36 h without any catalyst (entry 1), which indicated
that the catalyst was absolutely necessary for the Mannich-
type reaction. When the amount of [DDPA][HSO4] was
increased, a ramp in the yield of Mannich base was clearly
observed. The optimum amount of [DDPA][HSO4] was
1.0 mmol (10 mol% based on cyclohexanone) (entry 5), and
increasing the amount of catalyst beyond this led to no sub-
stantial improvement in the yield (entry 6).
The SO3H-functionalized ionic liquid [DDPA][HSO4]
was synthesized according to our previous method [29]
with some changes.
3-(N,N-Dimethyldodecylammonio)propanesulfonate
(C17H37NO3S)
To
a solution of 21.3 g N,N-dimethyldodecylamine
(0.10 mol) in 50 cm3 1,2-dichloroethane was added
12.2 g 1,3-propanesulfone (0.10 mol), in portions, within
15 min. The mixture was then stirred under nitrogen for
2 h at 55–60 °C. The white precipitate thus formed was
cooled to room temperature, and then isolated by filtration
and washed with petroleum ether. The product was
recrystallized from a mixture of water, ethanol, and diethyl
ether to give 98% yield of white solid product, mp 300–
302 °C (dec) with darkening at 300 °C.
Subsequently, the scope of the Mannich-type reaction of
other aromatic aldehydes 1, aromatic amines 2, and ketones
3 in the presence of [DDPA][HSO4] was investigated under
the optimized reaction conditions (Table 3). In general, the
three-component Mannich-type reaction proceeded
smoothly to give the corresponding products in reasonable
to good yields ranging from 77 to 96%. For aromatic
ketones, aromatic aldehydes carrying either electron-with-
drawing or electron-donating substituents could facilitate
Mannich-type reaction, and gave almost the same yields
(entries 15–19). For cyclohexanone, however, aromatic
3-(N,N-Dimethyldodecylammonio)propanesulfonic acid
hydrogen sulfate (C17H39NO7S2)
To a solution of 33.6 g 3-(N,N-dimethyldodecylammo-
nio)propanesulfonate (0.10 mol) in 10 cm3 water was
added 10.0 g sulfuric acid solution (98%) (0.10 mol).
The mixture was then stirred for 2 h at 80 °C. The
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