Experiment 9: Preparation of Methyl Salicyclate
O
O
H2SO4
OH
OCH3
+ CH3OH
OH
OH
+ H2O
Wintergreen (methyl salicylate) Gaultheria procumbens This tiny, North American
plant of the heath family grows in pine forests and on humid ground with sphagnum.
The Indians knew its effects, which is due to methyl salicylate. Like salicylic acid,
it is analgesic and antipyretic.
O
OCH3
HO
*bottle
Experimental setup: total reflux
Vacuum Distillation
OCH3
O
HO
BP 222 °C at 100 kPa
Vapor Pressure vs Temperature of Water
250
At what temperature will it boil
at 10 kPa?
Vapor Pressure (kPa)
200
150
P/kPa
100
50
0
0
20
40
60
80
100
120
140
Temperature, °C
Rule of thumb: BP decreases
by 10 °C each time the atm
pressure decreases by ½.
T/ C
100
22
50
210
25
200
12.5
190
6.3
180
3.1
170
1.6
160
0.8
150
0.4
140
How do I go about figuring out what my unknown is?
1. From your solubility measurements, you should be able to
classify your unknowns according to the solubility classes
discussed.
2. Look up some reference IR spectra in your manual that have
the possible functional groups present in your unknown.
3. Look up some possible classification tests you can run to
confirm their presence.
4. Complete and hand in your preliminary report if you haven’t
done so.
5. Select a possible derivative based on the properties of the
derivative. For example, choose a derivative that will allow
you to distinguish between other possible compounds with
melting points (±5 C) or boiling points (±10 C) within the
value of your unknown
Classification Tests
Classification test should only be run to confirm your suspicions
regarding the presence of a functional group suggested by your solubility
tests or IR. Always run a blank and a known at the same time you run
your unknown so that you know what a positive test looks like and that
you performed the classification test properly.
Derivatives
A derivative should be chosen whose melting temperature will allow you
to differentiate between possible compounds. If you have a carboxylic
acid or an amine, a titration can be substituted for a derivative providing
that the molecular weights of other possible compounds in your
possibility list can be excluded on the basis of your titration results.
What information can we deduce from this spectrum?
100
% Transmittance
80
60
40
20
1718 cm-1
0
4000
3500
neat liquid
3000
2500
2000
-1
Wavenumbers, cm
1500
1000
500
What information can we deduce from this spectrum?
100
% Transmittance
80
60
40
20
0
4000
3500
3000
2500
2000
-1
Wavenumber cm
KBr disk
1500
1000
500
100
% Transmittance
80
60
carbon-carbon
triple bond stretch
40
20
0
4000
3500
3000
2500
2000
-1
Wavenumbers, cm
neat liquid
1500
1000
500
100
% Transmittance
90
80
70
60

50
40
sp2 C-H stretches
overtones of
the benzene
ring
3
sp C-H stretches

30
20
4000
3500
3000
2500
2000
Wavenumbers, cm-1
The following is a liquid hydrocarbon

1500
1000
100
% Transmittance
80
60
40
20
Top: CHCl3 vs CHCl3
Bottom: 5% in CHCl3
0
4000
3500
3000
2500
2000
Wavenumbers, cm-1
The compound contains nitrogen
1500
1000
500
100
% Transmittance
80
60
40
20
0
4000
3500
3000
2500
2000
1500
-1
Wavenumbers, cm
Compound contains C, H, O
1000
500