Meilen, 16.12.2007
Organic chemistry practical course (OCPI)
HS 07
529-0229-00
Fabienne Vukotic
06-910-541
D-BIOL
Assistant: Guo Xiaoqiang
Synthesis of
Triphenylmethanol
1. Method
The method for the synthesis of Triphenylmethanol is a Grignard reaction with
benzophenone and phenylmagnesium bromide as the Grignard reagent.
2. Reaction Equation
O
H
Mg
Br
+
OH
3. Mechanism
Grignard reaction
Br
_.
+1
Br + Mg
0
+
Mg

Et 2 O

Br

Mg
OEt2
Et2 O
O
Ligand exchange
- Et2 O
(Mg as a Lewis acid,
carbonyl group as Lewis base)
Et 2 O

O
Mg

Mg
OEt 2

Br
Et2 O
+
Mg
Et 2 O
Br
Br
- Et2 O
Mg
O
recovery of
Grignard reagent
+ 2 Et 2 O

-

Br

Mg
Et2 O
Et 2 O
OEt2
O
Mg
+
Et 2 O
OEt 2
Et 2 O
O
Mg
Br
Mg
Br
Ligand exchange
Et2 O
Et 2 O
+ H3 O
OH
Br
4. Physical and Chemical Properties of Substances
Calcium chloride
dihydrate
CAS: 10035-04-8
M = 147.02g/mol
ρ = 0.70 g/mL
mp = 175 C
Risk phrases
- R36: Irritating to the eyes
Safety phrases
- S22: Do not breathe dust
- S24: Avoid contact with skin
Magnesium
CAS: 7439-95-4
M: 24.31 g/mol
bp: 1090 °C
mp: 648 °C
CH-toxicity class: free
Mg
Risk Phrases
-R11: Highly flammable
-R15: Contact with water liberates extremely
flammable gases
Safety Phrases
-S7/8: Keep container tightly closed and dry
-S43: n case of fire, use ... (indicate in the space
the precise type of fire-fighting equipment. If
water increases the risk add - Never use water)
Iodine
CAS: 7553-56-2
M: 253.81 g/mol
bp: 184 °C
d: 2.00 g/mL at 25 °C
mp: 113 °C
MAK: 1 mg/m3, 0.1 mL/m3
CH-toxicity class: 2
Risk Phrases
-R20/21: Harmful by inhalation and in contact
with skin
-R50: Very Toxic to aquatic organisms
I2
Safety Phrases
-S23: Do not breathe gas/fumes/vapor/spray
(appropriate wording to be specified by the
manufacturer)
-S25: Avoid contact with eyes
-S61: void release to the environment. Refer to
special instructions safety data sheet
Diethyl ether
(anhydrous)
CAS: 60-29-7
M: 74.12 g/mol
d: 0.706 g/mL
bp: 34.6 °C
mp: -116 °C
n20D: 1.3530
MAK: 1200 mg/m3, 400 mL/m3
CH-toxicity class: 4
Risk Phrases
-R12: Extremely Flammable
-R19: May form explosive peroxides
-R22: Harmful if swallowed
-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
-S29: Do not empty into drains
-S33: Take precautionary measures against static
discharges
Bromobenzene
CAS: 108-86-1
M: 157.01 g/mol
d: 1.491 g/mL
bp: 156 °C
mp: -31 °C
n20D: 1.559
CH-toxicity class: 3
Risk Phrases
-R10: Flammable
-R38: Irritating to the skin
-R51/53: Toxic to aquatic organisms, may cause
long-term adverse effects in the aquatic
environment
Safety Phrases
-S61: Avoid release to the environment. Refer to
special instructions safety data sheet
Phenylmagnesium
bromide
CAS: 100-58-3
M: 181.31 g/mol
d: 1.01 g/mL at 25 °C
Risk Phrases
-R12: Extremely flammable
-R14/15: Reacts violently with water, liberating
extremely flammable gases.
-R22: Harmful if swallowed
-R34: Causes burns.
-R67: Vapours may cause drowsiness and
dizziness.
Safety Phrases
-S16: Keep away from sources of ignition – no
smoking
-S33: Take precautionary measures against static
discharges.
S36/37/39: Wear suitable protective clothing,
gloves and eye/face protection.
-S43B: In case of fire, use fire-fighting equipment
on basis of sodium chloride or sodium
bicarbonate (never use water
-S45: In case of accident or if you feel unwell,
seek medical advice immediately (show label
where possible)
-S6A: Keep under nitrogen
S7/8: Keep container tightly closed and dry
Benzophenone
CAS: 119-61-9
M: 182.22 g/mol
d: 0.70 g/mL
CH-toxicity class: 4
bp: 305 °C
mp: 47-51 °C
Risk Phrases
-R36/37/38: Irritating to eyes, respiratory system
and skin
-R52/53: Harmful to aquatic organisms, may
cause long-term adverse effects in the aquatic
environment
Safety Phrases
-S26: In case of contact with eyes, rinse
immediately with plenty of water and seek
medical advice
-S61: Avoid release to the environment. Refer to
special instructions safety data sheet
Hydrochloric acid (6M
CAS: 7647-01-0
M = 36.46g/mol
ρ = 1.06g/mL at 25 C
CH toxicity class: 2
MAK: 5ml/m3, 7mg/ml3
bp =85 °C
mp = -25 °C
Risk-phrases
- R34: Causes burns
- R37: Irritating to the respiratory system
Safety-phrases
- S26: In case of contact with eyes, rinse
immediately with plenty of water and seek
medical advice
- S36/37/39: Wear suitable protective clothing,
gloves and eye/face protection
- S45: In case of accident or if you feel unwell, seek
medical advice immediately (show label where
possible)
HCl (aq.)
Sodium bicarbonate
CAS: 144-55-8
O
mp = 270 °C
+
Na
HO
M = 84.01g/mol
ρ = 2.16 g/mL at 25 °C
CH toxicity class: 5
O
-
Sodium chloride
CAS: 7647-14-5
NaCl
Sodium sulfate
CAS: 7757-82-6
Safety phrases
S24/25: Avoid contact with skin and eyes
M = 58.44g/mol
bp =1413 °C
ρ = 1.37g/mL
mp = 801 °C
CH toxicity class: non-toxic
Safety phrases
S24/25: Avoid contact with skin and eyes
M = 142.04g/mol
ρ = 2.68 g/mL at 25 °C
CH toxicity class: 5
mp = 884 °C
Triphenylmethanol
CAS: 76-84-6
M: 260.33 g/mol
d: 0.90 g/mL
bp: 142 °C
mp: 160-163 °C
Risk Phrases
-R38: Irritating to the skin
Safety Phrases
-S22: Do not breathe dust
-S24/25: Avoid contact with skin and eyes
5. Experimental Setup
reflux:
vacuum filtration:
20o
20o
safety bottle
500 mL
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]
[g]
Magnesium
0.45
Iodine
1 crystal
Diethyl ether
60
(anhydrous)
Bromobenzene
1.75
2.61
Benzophenone
2.1518
HCl
3
Benzophenone is the limiting reactant.
[mmol]
eq
18.5
2.9
catalyst
solvent
16.6
6.3
18
2.6
1.0
2.9
7. Experimental Section (Procedure)
In a 250 mL 3-neck round bottom flask, 0.45 g (2.9 eq.) of magnesium slivers,
on I2 crystal, and 20 mL of anhydrous Et2O are stirred together. Actually, it
would have been better to take only have as much Et2O. The liquid turns
yellow. A solution of 1.75 mL (2.6 eq.) in 20 mL of anhydrous Et2O is added
dropwisely. It now starts to reflux ,which means that the reaction has started.
The mixture is heated at 35 °C for 15 min and the mixture first becomes milky
grey and later it turns to a brownish color; the magnesium is dissolved, now.
2.1515 g (1.0 eq) in 20 mL anhydrous Et2O is added slowly. The solution is now
pink but after 1 min it suddenly turns to a soft pink and gets lighter and lighter
until it is white. The solution is acified to a pH below 1 with 3 ml of a 6M HCl
solution. The color turns to yellow and becomes clear and darker with a
second phase which is still milky, light yellow. The two phases are separated in
an extraction funnel and the aqeous phase is washed with Et2O (2x 25 mL).
The organic phases are collected, washed with saturated NaHCO3 (aq.) (2x
25 mL) and with saturated NaCl (aq.) (1x 25 mL), and dried over MgSO4. The
solution is filtered and then concentrated by evaporation of the solvent. The
curde product is purified by column chromatography (SiO2, Hexan/EtOAc
20:1 → 5:1, Rf ≈ 0.29, Hexan/EtOAc 10:1) The fractions with the pure product
are collected, the solvent is evaporated and the product is characterized.
8. Yield
The theoretical yield is 6.3 mmol. The experimental yield is 1.73 g = 6.65 mmol.
The yield percentage therefore is %
9. Characterization
Melting point
A melting point range of 152.5 -156.1 °C was measured. The literature value
for triphenylmethanol is 160 -163 °C.
IR-Spectrum (see attachement)
bands [cm-1]
3469
3059
1596
1489
1444
interpretation
O-H
C-H (aromatic)
C-C
Literature spectrum
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
10. Remarks and Discussion
Due to the long procedure the experimental cannot be very high. The
measured melting point does not correspond with the literature value,
however, by comparing the measured IR spectrum with the literature
spectrum the product can be clearly identified as triphenylmethanol.
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>.