Laboratory Report
Organic chemistry practical course (OCP1)
HS 07/08
26.11.2007
Lorenz Schwarzer
D-Biol
Assistant: Zhu Liang
Synthesis of Crystal Violet
(Methyl Violet 2B)
CH3
CH3
N
N
H3C
CH3
+
N
H3C
CH3
Method
Addition of Grignard-compounds: Addition of 4-bromo-N,N-dimethylaniline
(C8H10BrN) to diethyl carbonate, catalyzed by magnesium.
Reaction equation
CH3
CH3
N
N
H3C
CH3
O
CH3
Br
Mg
+
N
H3C
O
O
CH3
CH3
+
N
H3C
(C8H10BrN)
diethyl carbonate
CH3
crystal violet
Mechanism
N
N
Br
O
Mg
O
O
O
O
O
Br
H
N
MgBr
MgBr
O
O
O
HgBr
Br
O
N
Mg
O
O
O
H
N
N
N
MgBr
O
O
N
N
H
N
H
N
HN
N
H
N
H
N
N
O
OH
N
N
N
H
N
N
N
2
Physical properties of the substances
Magnesium
Molar weight
Density
Melting point
Boiling point
R-Phrases
24.31
1.74
650
1090
g/mol
g/ml
°C
°C
R11
R20
R22
S16
highly flammable
Harmful by inhalation
Harmful if swallowed
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
S33 Take precautionary measures
against static discharges
S36/37/39 Wear suitable protective
clothing, gloves and eye / face
protection
S-Phrases
Mg
Tetrahydrofuran THF
Molar weight
Density
Melting point
Boiling point
R-Phrases
O
72.11
0.889
-108.4
66
g/mol
g/ml
°C
°C
R11 Highly flammable
R19 May form explosive peroxides
R36-38 Irritating to eyes and.
S16 keep away from sources of
ignition – no smoking
S29 Do not empty into drains
S33 Take precautionary measures
against static discharges
S-Phrases
4-bromo-N,N-dimethylaniline
Molar weight
Density
CH3
Melting point
Br
N
Boiling point
R-Phrases
CH
R22
R33
-
3
S-Phrases
3
200.08 g/mol
- g/ml
54 - 55
°C
264
°C
harmful if swallowed
Danger of cumulative effects
Iodine
Molar weight
Density
Melting point
Boiling point
R-Phrases
126.90 g/mol
4.93 g/ml
113.7
°C
184.3
°C
R21 Harmful in contact with skin
R23 Toxic by inhalation
R25 Toxic if swallowed
R 34 Causes burns
S23 Do not breathe vapour
S25 Avoid contact with eyes
I
S-Phrases
Diethyl carbonate
Molar weight
Density
Melting point
Boiling point
R-Phrases
O
H3C
O
O
CH3
118.13
0.975
-43
126-128
g/mol
g/ml
°C
°C
R10 Flammable
R36-38 Irritating to eyes, skin and
respiratory system
S16 keep away from sources of
ignition – no smoking
S26 In case of contact with eyes, rinse
immediately with plenty of water
S36 Wear suitable protective clothing
S-Phrases
Hydrochloric acid (HCl)
Molar weight
Density
Melting point
Boiling point
R-Phrases
H-Cl
36.46
1.19
-40
84
g/mol
g/ml
°C
°C
R 34 Causes burns
R36-38 Irritating to eyes, skin and
respiratory system
S 26 In case of contact with eyes, rinse
immediately with plenty of water
S-Phrases
Crystal violet
CH3
CH3
N
N
H3C
CH3
Molar weight
Density
Melting point
Boiling point
R-Phrases
R22
R25
R40
R41
S26
+
N
H3C
CH3
S-Phrases
S39
4
407.88 g/mol
- g/ml
Decomposes (ca. 140-215)
°C
°C
harmful if swallowed
Toxic if swallowed
Limited evidence of a
carcinogenic effect
Risk of damage to the eyes
In case of contact with eyes, rinse
immediately with plenty of water
Wear eye / face protection
Educts
Substance
Amount
Magnesium
4-bromo-N,Ndimethylaniline
Diethyl carbonate
Molar amount
Volume
g
0.32
2.03
mol
0.013
0.010
ml
0.18
-
0.20
0.0017
0.21
Experimental accomplishment
1. Into a 250 ml flask (rinsed before with some THF), 0.32 g magnesium, 18 ml
THF, 2.03 g 4-bromo-N,N-dimethylaniline and one crystal iodine were added.
The solution became green.
2. It was heated gently under reflux for 30 min. The colour changed to browngreen. And then cooled down to room temperature.
3. 0.20 g diethyl carbonate in 2 ml THF (in one portion) was added and heated
again to reflux for 5 min. Then cooled down to room Temperature.
4. Slowly 6 ml of aqueous HCl (10 % solution) was added.
5. A piece of cotton was coloured by the crystal violet. But with soap it was
possible to wash out the colour.
6. The water was evaporated, a plastic violet mass with metal shine originated.
7. The mass was dried in the oven and the IR and the melting point were
measured. It was not possible to measure the yield, because the crystal violet
was very hard and clinged to the bottom of the flask.
Experimental setup
Thermometer
Reflux condenser
Thermometer
Condenser
Vacuum
Oilbath
4
3
21
5 67
8
11 9
4
3
2
1
5 67
8
9
1
0
Heating Apparatus
4
3
21
5 67
8
11 9
4
3
2
1
5 67
8
9
1
0
Distillation Apparatus
5
Results
Melting point:
Taken:
Crystal violet (lit.):
4-bromo-N,Ndimethylaniline (lit.):
IR-Spectrum-bands [cm-1]
159°C
ca. 140-215°C
54 - 55°C
1580
1514.57
1354.46
1296.26
1164.25
1059.54
C-C in-ring
C-C in-ring
C-H rock
C-N stretch
C-N stretch
C-N stretch
(aromatics)
(aromatics)
(alkanes)
(aromatic amines)
(aliphatic amines)
(aliphatic amines)
With the aid of the interpretation of the IR-spectrum, the product can be identified as
a molecule with aromatic rings and amines.
But it’s not possible to distinguish clearly between 4-bromo-N,N-dimethylaniline and
crystal violet, because there are no different bounds which could be measured.
But with the taken melting point, the product can be identified as crystal violet,
because the melting point of 4-bromo-N,N-dimethylaniline is much lower.
IR-Spectrum of the Product
6
Reference IR-spectrum of crystal violet
Literature






Script Organic chemistry II, Prof. Dr. Hans-Jürg Borschberg, ETH Zürich
Table of Characteristic IR Absorptions
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_index.cgi?lang=eng
http://en.wikipedia.org
http://www.discoverygate.com
http://physchem.ox.ac.uk/MSDS/#R%20and%20S
7