Meilen, 4.12.2007
Organic chemistry practical course (OCPI)
HS 07
529-0229-00
Fabienne Vukotic
06-910-541
D-BIOL
Assistant: Guo Xiaoqiang
Synthesis of
Dibenzalacetone
(1,5-Diphenyl-1,4-pentadien-3-one)
1. Method
The method for the synthesis of Dibenzalacetone is a mixed aldole
condensation of one equivalent acetone with two equivalent benzaldehyde.
Sodium hydroxide acts as the basic catalyst.
2. Reaction Equation
O
O
O
2
H
NaOH
+
3. Mechanism
Aldole condensation (base catalyzed)
O
OH
H
O
H
H
OH
- H2 O
O
O
H
H
- H2 O
trans-elimination*
O
OH
O
O
O
H
O
H
OH
- H2 O
- H2 O
trans-elimination*
O
*
HO
H
trans-elimination:
OH
COR
H
ROC
this is what actually happens
H
Phe
HO
H
H
Phe
H
H
OH
H
cis-elimination:
H
Phe
H
COR
HH
Phe
COR
this is impossible because the
staggered conformation is
sterically extremely hindered
4. Physical and Chemical Properties of Substances
Sodium hydroxide
CAS: 1310-73-2
M: 40.00 g/mol
mp: 318 °C
CH-toxicity class: 2
Risk Phrases
-R35: Causes severe burnsIrritating to eyes,
respiratory system and skin
Safety Phrases
-S26: In case of contact with eyes, rinse
immediately with plenty of water and seek
medical advice
-S37/39: Wear suitable gloves and eye/face
protection
-S45: In case of accident or if you feel unwell,
seek medical advice immediately (show label
where possible)
Ethanol
CAS: 64-17-5
M: 46.07 g/mol
d: 0.789 g/mL at 25 °C
bp: 78 °C
n20D: 1.3600
MAK: 1900 mg/m3, 1000 mL/m3
CH-toxicity class: free
Risk Phrases
-R11: Highly flammable
-R20/21/22: Harmful by inhalation, in contact
with skin and if swallowed
Safety Phrases
-S7: Keep container tightly closed
-S16: Keep away from sources of ignition - No
smoking
-S36/37: Wear suitable gloves and eye/face
protection
Benzaldehyd
CAS: 100-52-7
M: 106.12 g/mol
d: 1.045 g/mL at 25 °C
CH-toxicity class: 4
bp: 178-179 °C
n20D: 1.545
Risk Phrases
-R22: Harmful if swallowed
Safety Phrases
-S24: Avoid contact with skin
Acetone
CAS: 67-64-1
M: 58.08 g/mol
d: 0.791 g/mL at 25 °C
bp: 56 °C
n20D: 1.359
MAK: 2400 mg/m3, 1000 mL/m3
CH-toxicity class: 5
Risk Phrases
-R11: Highly flammable
-R36: Irritating to the eyes
-R66: Repeated exposure may cause skin
dryness or cracking
-R67: Vapors may cause drowsiness and dizziness
Safety Phrases
-S9: Keep container in a well-ventilated place
-S16: Keep away from sources of ignition - No
smoking
-S26: In case of contact with eyes, rinse
immediately with plenty of water and seek
medical advice
Acetic acid
CAS : 64-19-7
M: 60.05 g/mol
d: 1.049 g/mL at 25 °C
bp: 117-118 °C
mp: 16.2 °C
n20D: 1.3716
MAK: 25 mg/m3, 10 mL/m3
CH-toxicity class: 4
Risk Phrases
-R10: Flammable
-R35: Causes severe burns
Safety Phrases
-S23: Do not breathe gas/fumes/vapor/spray
(appropriate wording to be specified by the
manufacturer)
-S26: In case of contact with eyes, rinse
immediately with plenty of water and seek
medical advice
-S45: In case of accident or if you feel unwell,
seek medical advice immediately (show label
where possible)
Dibenzalacetone
CAS: 538-58-9
M: 234.29 g/mol
mp: 104-107 °C
5. Experimental Setup
reflux:
vacuum filtration:
20o
20o
safety bottle
500 mL
100
mL
75
50
25
NS 14
20o
250 mL
LaboBib©
300
50
AN
AN
AUS
AUS
1500
0 U/min
250
500
100
o
C
200
150
1000
750
vacuum
6. Amounts of Substance used
Substance
measured
amount [ml]
2.40
0.90
25
6.5
[g]
[mmol]
eq
Benzaldehyde
2.51
23.6
2.0
Acetone
0.71
12.3
1.04
NaOEt (aq.)
Acetic acid in
EtOH (5%)
Benzaldehyde is the limiting reactant since it requires two equivalent for one
equivalent acetone.
7. Experimental Section (Procedure)
First, an aqueous ethanolic sodium hydroxide solution is prepared with 1.8 g
NaOH, 18.0 mL water and 13.5 mL 95% ethanol.
2.40 mL (2.0 eq.) Benzaldehyde and 0.90 mL (1.04 eq.) Acetone are
combined in a 50 mL two-neck round bottom flask. 25 mL of aqueous
ethanolic sodium hydroxide is added dropwisely with a dropping funnel. The
mixture is stirred at RT for 30min. The solution turns from clear to a milky light
yellow, which gets darker until it is orange, then turns back to light yellow as a
a light yellow precipitate forms. The crude product can is collected with
vacuum filtration and washed with a small amount of cold water. 20 mL of 5%
(v/v) acetic acid in ethanol is added to the solid product. When it is stirred,
clumps form. The product is vacuum filtered again and washed with ethanol.
Very light yellow, sparkling crystals are collected. The crystals are recristallized
in 6.5 mL 95% ethanol. The solution turns brownish. When it is allowed to cool
down to RT, bright yellow needle crystals form. The product is collected by
vacuum filtration and characterized.
8. Yield
The theoretical yield is 11.8 mmol. The experimental yield is 1.6565 g =
7.07 mmol.
The yield percentage therefore is 59.8%
9. Characterization
Melting point
A melting point range of 103.4 – 107.5 °C was measured. The literature value
for dibenzalacetone is 104 -107 °C.
IR-Spectrum (see attachement)
bands [cm-1]
3026
1672
1649
1589
1573
1494
1447
interpretation
unsat. C-H
C=O
C=C
C-C in the aromatic ring
Literature spectrum
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
10. Remarks and Discussion
The measured melting corresponds well to the literature value and the yield is
acceptable. The IR spectrum shows that the product is not entirely free of
water and ethanol (weak, broad band from 3600 – 3300 cm-1). Other than
that, the spectrum is very good and can be interpreted accordingly.
11. Literature
Coblentz Society, Inc., "Evaluated Infrared Reference Spectra" in NIST
Chemistry WebBook, NIST Standard Reference Database Number 69,
Eds. P.J. Linstrom and W.G. Mallard, June 2005, National Institute of
Standards and Technology, Gaithersburg MD, 20899. NIST Chemistry
Webbook. 4 Dec. 2007 <http://webbook.nist.gov>.
EMolecules - Searching the World's Chemistry. 2007. EMolecules, Inc. 4 Dec.
2007 <http://www.emolecules.com>.
IGS Giftliste. 31 July 2007. BAG. 4 Dec. 2007
<http://igs.naz.ch/igs/igsServer/de.kisters.igs.igs40.servlets.igs40Servlet>.
Kirste, Burkhard. "Chemikalien: Sicherheitsdaten." Institut für Chemie und
Biochemie an der FU Berlin. 28 July 1994. FU Berlin. 4 Dec. 2007
<http://www.chemie.fu-berlin.de/chemistry/safety/chemsafety.html>.
"Risk & Safety." Sigma-Aldrich. 2007. Sigma-Aldrich Co. 4 Dec. 2007
<http://www.sigmaaldrich.com/Help_Pages/Help_Welcome/Product_
Search/Risk___Safety_Statements.html#Safety%20Phrases>.
Sigma-Aldrich. 2007. Sigma-Aldrich Co. 4 Dec. 2007
<http://www.sigmaaldrich.com/Area_of_Interest/Europe_Home/
Switzerland__Schweiz_.html>.