Vol. 27, No. 9 (2015)
Efficient Synthesis of α-Hydroxyacetophenone 3187
TABLE-4
EFFECT OF CATALYST TYPE IN THE SYNTHESIS OF α-HYDROXYACETOPHENONEa
Entry
Reaction type
MW P10
MW P10
MW P30
MW P30
MW P30
MW P30
MW P30
MW P30
MW P50
Catalyst
-
Tetrabutylammonium chloride
-
Tetrabutylammonium chloride
Tetrabutylammonium bromide
Polyethylene 400
Conv. (%)b
Yield (%)b
4.6
1
2
3
4
5
6
7
8
9c
5.1
38.3
29.7
51.6
32.8
36.4
35.7
40.9
36.4
27.3
49.8
30.1
35.0
34.3
39.2
83.7
Benzyltriphenylphonium ammonium chloride
Polyethylene 20000
Tetrabutylammonium chloride
85.7
aα-Bromoacetophenone (0. 5 mmol) in water (10 mL) was irradiated by microwave for 10 min; bYields were determined by GC with 4-nitrotoluene
as internal standard; cα-Bromoacetophenone (0. 5 mmol) in water (10 mL) was irradiated by microwave
of 1,4-dioxane. HBr/H2O2 system has many advantages, such
as simple experimental procedure, high yields of α-bromo-
acetophenone, a lower impact on the environment since
bromine is generated in situ from HBr/H2O2. The synthesis of
α-hydroacetophenone is also simple, clean and environment
friendly. Microwave reaction was found significantly to improve
the α-hydroacetophenone yield and shorten the reaction time
of the key step reactions.
yield, several phase transfer catalysts were also tested (Table-4,
entry 4-8). When the reaction was carried out with tetrabutyl-
ammonium chloride as phase transfer catalyst, the conversion
and yield were higher than others and the conversion got to
85.7 %, the yield of α-hydroxy acetophenone obtained 83.7 %.
This could be ascribed to that tetrabutylammonium chloride
was better dissolving in both aqueous phase and organic phase
than other catalysts, it accelerated the hydrolysis of α-bromo-
acetophenone and improved the yields.
It was also found that microwave power played an impor-
tant role in improvement of the reaction. The conversion and
yield of α-hydroxyacetophenone under different microwave
power in water were summarized in Table-5.
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TABLE-5
EFFECT OF MICROWAVE POWER IN THE
SYNTHESIS OF α-HYDROXYACETOPHENONEa
Entry
Reaction type
MW P10
MW P30
MW P50
MW P80
Conv. (%)b
-
Yield (%)b
-
1
2
3
4
5
40.1
85.7
89.3
88.9
37.6
83.7
77.2
73.1
MW P50
aα-Bromoacetophenone (0. 5 mmol) in water (10 mL) was irradiated
by microwave for 5 min; bYields were determined by GC with 4-
nitrotoluene as internal standard
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As can be seen from Table-5, it was found that with the
microwave power rising, the conversion and yield were signifi-
cantly increasing (Table-5, entry1-5). But when the microwave
power was MW P80 and MW P100 (Table-5, entry4-5), the yield
of α-hydroxyacetophenone were decline. Based on this result,
we inferred that when the microwave power was MW P80 and
MW P100, the reaction temperature got too high and α-hydroxy-
acetophenone was decomposition. Therefore, we selectted the
microwave power as MW P50.
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Conclusion
In summary, α-bromoacetophenon was highly selectively
prepared in high yield with a HBr/H2O2 system in the presence