Zurich, 04.12.2007
Synthesis of
Dibenzalacetone
O
Tobias Langenegger
tobiasla@student.ethz.ch
05-918-362
D-Biol (chem.)
assisted by
Guo Xiaoqiang
Method
Aldocondensation with acetone in basic solution.
Chemical equation
O
O
2
O
base
+
Mechanism
O
O
H
+
OH-
O
O
+
H
H
OH
O
O
- H 2O
H
HO-
O
O
+
O
- H2O
Physical and safety data
substance
Mw
(g/mol)
density
(g/cm3)
mp
(°C)
bp
(°C)
NaOH
(solved)
40
-
-
1.045
Benzaldehyde
106.1
R-phrases
S-phrases
-
Poiso
n
CH
3
35
26, 37, 39, 45
-
177
4
22
24
Acetone
56
0.791
-
55-57
5
11, 67
9, 26
Dibenzalacetone
234.3
-
111-113
-
-
10, 20, 22, 34
23, 26,45
Ethanol
46.07
0.79
-114.5
78.3
-
11
7, 16
Equipment
reflux:
vac. filtration:
Preparation
Substance
Benzaldehyde
Acetone
eq
1.863
1.0
n (mmol)
23.64
12.69
V (mL)
2.4
0.9
m (mg)
-
Experimental section
To a solution of 2.4 mL benzaldehyde and 0.9 mL acetone, 25 mL of aqueous
ethanolic sodium hydroxide (1.8 g NaOH in 18 mL water and 13.5 mL ethanol) were
added slowly over a drop funnel. The solution was stirred for 30 min at room
temperature and turned from white (cloudy) over a light yellow to a dark yellow.
Finally a yellow solid formed from the solution. This solid was collected by vacuum
filtration and washed with 6 pipettes of cold water. The solid was transferred to a
beaker with 20 ml 5% acetic acid in ethanol and stirred. Than it was vacuum filtrated
and washed with 3 pipettes of cold ethanol. The product was purified by
recrystallisation (2 x from 95% ethanol and 1 x from ethyl acetate), collected by
filtration and characterized.
Yield
V
-
m
0.35 g
n
1.494 mmol
Yield
12.%
Characterisation
Melting point
109.8 - 111.2 °C
(lit. 111 – 113 °C)
Peaks in IR spectrum
3025 cm-1
1649 cm-1
1588 cm-1
aromat
C=O
aromat
Discussion
After my first recrystallisation with 95% ethanol I didnʼt get only crystals. The biggest
part of my product was in form of viscous yellow oil. The IR and mp of the crystals I
got wehere ok. I tried a second time to recrystallize with ethanol, but the result was
the same. So I chanced the solvent and used ethyl acetate. And this third time, it
worked. The mp was little bit higher than the first time, so I think it was more pure.
I donʼt know exactly, why this problem happed but I think this could be because of
impurity.
Literature
http://chemfinder.cambridgesoft.com/
https://www.discoverygate.com/
http://www.chemexper.com/
http://www.wikipedia.org/
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
Attachment
-
Copy of the lab notebook
IR spectrum (once after the first recrystallisation and once after the last)
Reference IR spectrum
Reference IR spectrum
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi