JOURNAL OF CHEMICAL RESEARCH 2011 485
Table 2 Effects of reaction conditions on the yield of the
reaction catalysed by β-CD-[bmim]PF
out, and further work on ionic liquid as both catalyst and
solvent in this reaction is in progress.
6
Entry
T
°C
Time Ratioa
/h
β-CD:
cat./Reactant Yield
c d
/
ionic liquidb
/%
/%
Experimental
Mandelic acid (2a): Benzaldehyde, chloroform, and the phase transfer
catalyst were placed in a three-neck 100mL flask, and stirred in water
bath at 50 °C. Then 13 ml 50% aq. sodium hydroxide was added drop-
wise in 0.5h. After addition, the reaction was continued at 50 °C for
6 h. Then reaction mixture was quenched in 100ml water, and the
aqueous layer and organic layer were separated. The phase transfer
catalyst was separated from the organic layer by distillation under
reduced pressure and directly recycled for reuse. The aqueous layer
was acidified to a pH value of approximately one by using 50% aq.
sulfuric acid, and then extracted with the ethyl ether (15 mL×3).
The combined extracts were distilled to remove ethyl ether under
reduced pressure. After recrystallisation from toluene, pure crystalline
mandelic acid was obtained by filtration.
1
2
3
4
5
6
7
8
9
40
50
60
70
50
50
50
50
50
50
50
50
50
50
50
50
50
50
6
6
6
6
2
4
8
6
6
6
6
6
6
6
6
6
6
6
1:2
1:2
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
2:1
1:2
1:3
1:2
1:2
1:2
1:2
1:2
5
5
5
5
5
5
5
5
5
5
5
5
5
62
80
76
68
65
75
77
60
81
80
70
82
78
64
85
79
1:2
1:2
1:2
1:2
1:2
1:1
1:1.5
1:2.2
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
2.5
10
20
10
10
Melting points measured on MRS-1A apparatus are uncorrected.
IR spectra were recorded as KBr pellets on Nicolet IR 200 spectro-
1
photometer. H NMR spectra were determined on Bruker (400 MHz)
e
80f
spectrometer in DMSO-d using TMS as an internal standard.
6
60
−1
Mandelic acid (2a): IR(cm ) 3400, 2965, 2630, 1714, 1450, 1378,
a
b
1
Ratio of benzaldehyde to chloroform in mole. Ratio in mole.
1298, 1063, 731, 695. H NMR δ 12.55 (1H, s, -COOH), 7.18–
c
d
In mole fraction. Isolated yield based on benzaldehydes.
*
7
.27 (5H, m, ArH), 5.28 (1H, s, ArCH (OH)-), 3.63 (1H, brs,
e
f
Catalyst is reused twice. Catalyst is reused three times.
*
ArCH(OH )-).
−
1
1
p-Hydroxymandelic acid (2b): IR(cm ) 3415, 1621, 1384, 824. H
NMR δ 12.38 (1H, s, -COOH), 6.85 (2H, d, J=8.6Hz, ArH), 7.30 (2H,
*
d, J = 8.6 Hz, ArH), 5.33 (1H, s, ArOH), 5.40 (1H, s, ArCH (OH)-),
Finally, several substituted mandelic acids (2) were synthe-
sised from corresponding substituted benzaldehyde (1) and
chloroform under the above optimized conditions catalysed by
*
3
.68 (1H, brs, ArCH(OH )-).
p-Methoxymandelic acid (2c): IR(cm ) 3404, 2968, 1718, 1611,
−
1
1
1
514, 1392, 1258, 1179, 1072, 827. H NMR δ 12.37 (1H, s, -COOH),
the composite catalyst β-CD-[bmim]PF , and the results being
6
7.32 (2H, d, J = 8.6 Hz, ArH), 6.89 (2H, d, J = 8.6 Hz, ArH), 5.20 (1H,
listed in Table 3. It is shown that the composite phase transfer
*
*
s, ArCH (OH)-), 3.80 (3H, s, -OCH ), 3.45 (1H, brs, ArCH(OH )-).
3
−
1
catalyst β-CD-[bmim]PF was also applicable to reactions
3-Methoxy-4-hydroxymandelic acid (2d): IR(cm ) 3441, 3229,
6
1
of some substituted benzaldehyde with function group p-
hydroxyl, p-methoxyl, and 3-methoxyl-4-hydroxyl but p-nitryl
group. Melting points of the product 2 were consistent with
the literature data except 2e which is much more like to be
1732, 1525, 1377, 1150, 1033, 830. H NMR δ 12.41 (1H, s, -COOH),
*
7.02–7.30 (3H, m, ArH), 5.40 (1H, s, ArCH (OH)-), 5.37(1H, s,
*
ArOH), 4.01 (3H, s, -OCH ), 3.55 (1H, brs, ArCH(OH )-).
3
−
1
p-Nitrobenzoic acid (2e): IR(cm ) 2600–3400, 1692, 1606, 1534,
1
1
1
1
1351, 1310, 1294, 718. H NMR δ 13.69(1H, s, -COOH), 8.32(2H,
p-nitrobenzoic acid (lit. m.p. 236–240 °C), and H NMR
chemical shift for hydrogen of 2e can also verify that 2e is
not p-nitromandelic acid but p-nitrobenzoic acid. In fact, p-
nitromandelic acid is sporadically reported in the literature
and its synthesis, unlike that of its other isomer, is surprisingly
d, J = 8.8 Hz, ArH), 8.16(2H, d, J = 8.8 Hz, ArH).
Received 3 July 2011; accepted 10 August 2011
Paper 1100771 doi: 10.3184/174751911X13131678182481
Published online: 29 August 2011
1
2
difficult to synthesise. The strong electron-withdrawing of p-
nitryo group could lead severely to Cannizzaro reaction under
the employed experimental conditions to give p-nitrobenzoic
acid.
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In conclusion, a new procedure employing the composite
2
3
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6
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Table 3 Synthesis of 2 with composite β-CD-[bmim]PF
6
as
a
phase transfer catalyst.
Compound. Colour
Yield/%b
M.p./°C)
Lit. m.p. (°C)
117.3–118.513
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2
2
2
2
2
a
b
c
d
e
White
White
White
White
–
85
78
75
67
120–121
110–112
104–108
130–132
–
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4
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13
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12
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–
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2
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a
All reactions were performed at 50 °C with stirring for 6 h
under catalyst of 10% to benzaldehyde in mole fraction.
1
1
3
4
H. Xu and Y. Chen, Ultrason. Sonochem., 2008, 15, 930.
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b
Isolated yield based on benzaldehydes.
c
p-Nitromandelic acid was obtained as yellow solid with the
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1
1
yield 35%, m.p. 238–240 °C (lit. m.p. 236–240 °C).