Vol. 27, No. 1 (2015)
Efficient Synthesis of Benzoylformic Acid Under Mild Conditions 79
for an appropriate time. The catalyst was separated by filtration.
GC quantitative analyses of the filtrate extracts showed yield
of styrene oxide. The filtrate was diluted with deionized water
TABLE-1
SYNTHESIS OF STYRENE EPOXIDE
UNDER VARIOUS CATALYSTS
a
Conversion (%)
a,b
Yield (%)
Entry
Catalyst
–
(
50 mL) and extracted with ethyl acetate (10 mL × 3). The
1
2
> 99
91.0
95.0
87.0
> 99
> 99
> 99
> 99
22.5
39.2
Trace
73.4
combined organic phase was concentrated and subjected to
column chromatography on silica gel with a mixture of n-
hexane/ethyl acetate (10:1) which afforded pure epoxides.
Procedure for synthesis of 2-hydroxy-1-phenylethanone:
Into the solution of II (0.20 g, 1.6 mmol) in mixtures (5 mL)
of acetonitrile and water in 9:1 (v/v) was added cerium ammo-
nium nitrate (0.20 g, 0.36 mmol) then bromine sources (1 g)
at 30 °C with stir.After completion of the reaction, the mixture
was diluted with water and extracted with ethyl acetate (10
mL × 3). The combined organic extract was dried over sodium
sulfate and concentrated under vacuum. The product III was
purified by column chromatography on silica gel using n-
hexane/ethyl acetate (10:1) as eluent.
Mg Al (OH) CO
3
1
0
2
24
c
d
3
Mg Al (OH) CO
3
86.4
10
2
24
e
4
Mg Al (OH) CO
3
82.6
9.0
10
2
24
5
6
7
8
CuBEA-25
CoBEA-25
CuZSM-5
CoZSM-5
MoO3
17.1
11.0
11.9
22.1
52.8
f
9
10
MgO
a
b
Determined by GC using an internal standard technique; Based on the
c
styrene; The reaction was carried out with acetonitrile-benzene media
d
of volume ratio of 1 : 9 instead of acetonitrile as the solvent; Isolated
e
yield; The reaction was carried out with acetonitrile-formamide media
f
of volume ratio of 1 : 9 instead of acetonitrile as the solvent; The
reaction was carried out with tert-butyl hydroperoxide (2.4 mL) instead
of aqueous hydrogen peroxide as the solvent
Procedure for synthesis of benzoylformic acid: Into a
three-necked reaction flask with a reflux condenser were succe-
ssively placed III (0.45 g, 3.3 mmol), water (10 mL), phase
transfer catalyst (0.01 g) and 40 % aqueous hydrogen bromide
conversion were only obtained respectively. Therefore much
attention has been focused on developing the novel catalytic
processes based on efficient hydrotalcite catalysts with easy
workup. In the presence of Mg Al (OH) CO in acetonitrile-
(
0.75 g, 5 mmol). Then 30 % aqueous hydrogen peroxide
3 g, 26.7 mmol) was added dropwise to the mixture at room
(
10
2
24
3
temperature in no less than 0.5 h. The reaction was maintained
at 65 °C for defined time with vigorous stirring by TLC track.
After reaction, the mixture was cooled to room temperature
and product was extracted with ethyl acetate (15 mL × 3). The
combined organic layer was washed with dilute solutions of
sodium thiosulfate and dried with anhydrous sodium sulfate.
The sample was purified by silica gel column chromatography
using petroleum ether/ethyl acetate (95:5) as eluent.
benzene media of volume ratio of 1:9, the yield of styrene
epoxide could be promoted to 86.4 % of isolated yield in a
95 % substrate conversion (entry 3 in Table-1). Similarly the
yield could be raised to 82.6 % in acetonitrile-formamide media
of volume ratio of 1:9 (entry 4 in Table-1). It is likely that the
Brønsted basic sites derived from surface hydroxyl groups on
the hydrotalcite play an important role in the epoxidation of
9
-13
olefins in the presence of nitriles
Next, the synthesis of the desired a-hydroxyketone(III)
.
1
Styrene epoxide (II): Pale oil; H NMR (400 MHz,
14
CDCl
T, 1H).
-Hydroxy-1-phenylethanone (III): Pale yellow solid;
3
): δ = 7.33-7.30 (m, 5H), 3.9 (T, 1H), 3.1 (T, 1H), 2.8
began with substrate II using Rao's procedure . A 96 % of
yield was achieved with 30 % aqueous hydrogen peroxide,
cerium ammonium nitrate (CAN) and N-bromosuccinimide
in acetonitrile and water media (entry 1 in Table-2). It was
found that N-bromosuccinimide in reaction media play a key
role in promoting reaction selectivity. Especially, the moisture
was imperative since only trace of product was detected by
high performance liquid chromatography under anhydrous
conditions (entry 2 in Table-2). Other various bromine sources
such as potassium bromide, sodium bromide and hydrogen
bromide under similar conditions gave poor yield of α-hydroxy-
ketone (entries 3-5 in Table-2).
(
2
1
3
m.p. = 86-87 °C. H NMR (400 MHz, CDCl ): δ = 8.01-7.94
(
m, 2H), 7.70-7.64 (m, 1H), 7.58-7.56 (m, 2H), 4.79 (s, 2H),
3
.65 (s, 1H).
Benzoylformic acid (IV): White solid; m.p. = 62-63 °C.
H NMR (400 MHz, CDCl ): δ = 9.19 (s, 1H), 8.04-8.01 (m,
H), 7.73-7.70 (m, 1H), 7.54-7.52 (m, 2H).
1
3
2
RESULTS AND DISCUSSION
First of all, the feedstock styrene (I) was conveniently
transferred styrene epoxide (II) by employing aqueous
hydrogen peroxide as oxidant over various catalysts shown in
Table-1.
TABLE-2
SYNTHESIS OF 2-HYDROXY-1-PHENYLETHANONE
UNDER SOME BROMINATION REAGENTS
It could be seen that the selectivity of epoxidation in a
1.0 % of substrate conversion could reach relatively high level
a
Entry Bromination reagent Time (h) Conversion (%) Yield (%)
a
9
b
1
NBS
NBS
HBr
4
> 99
> 99
> 99
> 99
> 99
96.0
Trace
16.6
59.6
19.2
in a yield of 73.4 % over hydrotalcite catalyst (entry 2 in
Table-1) compared with blank and other solids. From Table-1,
epoxidation was rather feeble in the absence of any catalyst
c
2
10
4.5
5
3
4
5
KBr
(
entry 1 in Table-1). Surprisingly, the reaction selections were
NaBr
4.5
a
poor to epoxidation although a 100 % conversion could be
obtained in the presence of metal ion-exchanged zeolites cata-
lysts (entries 5-8 in Table-1). We also selected metal oxides as
catalysts to apply to the preparation of styrene epoxide (entries
Calculated from HPLC peak area
Finally, the formation of benzoylformic acid (IV) was
extensively optimized under reaction conditions involving
different amount ratios of III to aqueous hydrogen peroxide,
9, 10 in Table-1). And 22.1 and 52.8 % yields in low substrate