Lecture 7
Ch 6: Distillation & Boiling Points
This Week In Lab:
• Ch 5: Extraction, Procedure 2
• Ch 4 Final Report Due
Next Week in Lab:
• Ch 6 PreLab due
• Ch 6: Procedure 1 & Procedure 2 (if time)
• Quiz 3
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Distillation & Boiling Point
Distillation:
• Purification technique
• Used to separate components of a liquid mixture or to purify an
impure liquid
• Several basic types/variations:
• Simple distillation
• Fractional distillation
• Simple, high vacuum distillation
• Steam distillation - used to co-distill compounds with water
Boiling Point:
• Physical property of a compound
• Used to identify an unknown
2
The Distillation Experiment: Ch 6
A two-day lab
Day One: Procedures 1 & 2
•
•
•
Steam distillation of a spice
Bioassay of spice oil to assess antibacterial property of oil
Analyze GC-MS data of spice oil
Day Two: Procedure 3
•
•
Microscale fractional distillation of an unknown mixture
Identify the two components of the mixture via boiling point &
solubility tests
Outside of Lab Time: Procedure 4
•
•
Work with two data sets: simple distillation data and fractional
distillation data
Compare simple and fractional distillations
3
The Distillation Experiment: Ch 6
Day One:
Steam distillation of a spice (Procedure 1):
•
Choose a spice: clove, tumeric or nutmeg
•
Build the steam distillation set-up: see Figure 6.3
•
Spice oils will co-distill with water! Each oil will contain at least two
main compounds.
Extract oil from water using dichloromethane (same technique used in
extraction of caffeine).
4
Steam Distillation Set-Up
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
5
The Distillation Experiment: Ch 6
Day One or Day Two:
Bioassay of spice oil (Procedure 2):
•
Use prepared sterile agar plates
•
Inoculate plates with a Bacillus cereus solution.
•
Share an agar plate with your hood mate!
•
Observe any inhibition of bacterial growth around the spice oil.
Assess results after 24 hrs to
1 week.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Measure the distance of
inhibition
6
GC-MS Data
You will be given the GC-MS data for your spice oil.
Look at the GC chromatogram:
• Look at the number of major signals (25% relative abundance or higher).
The number of major signals = the number of main compounds in the oil.
• Look at the retention times. In general, the higher the retention time, the
higher the boiling point/FW of that compound.
Look at the mass spectrum:
• Look for M+ (molecular ion peak); M+ equals the FW for that compound.
• You will determine the identities of the compounds in your oil by looking
at the list of possibilities.
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GC-MS Data
Possible compounds in the oils:
OH
OCH3
OCH3
OCH3
H3CO
O
OCH3
O
Allyl methoxybenzodioxole
FW = 192
Eugenol
FW = 164
bp = 254°C
O
Allyl trimethoxybenzene
FW = 208
Ar-Tumerone
FW = 216
O
O
Caryophyllene
FW = 204
bp = 262-264°C
Curlone
FW = 218
Tumerone
FW = 218
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Nutmeg Oil GC-MS Data
Gas chromatogram of
Nutmeg oil
Two major compounds:
A&B
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Note retention times &
Relative abundances:
A is 14.14 minutes, 100%
B is 14.49 minutes, 40%
Most likely, B has a higher bp
and/or FW than A.
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Nutmeg Oil GC-MS Data
Mass Spectrum of A
M+ at 192
Compound is:
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
OCH3
O
O
Allyl methoxybenzodioxole
FW = 192
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Nutmeg Oil GC-MS Data
Mass Spectrum of B
M+ at 208
Compound is:
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
OCH3
H3CO
OCH3
Allyl trimethoxybenzene
FW = 208
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Steam Distillation: Natural Product Isolation
Steam distillation of citral from lemon grass oil
Citral (oil) comprised of:
CH3
CH3
CHO
H3C
Geranial
CH3
CH3
H3C
Neral
Uses of citral:
• Defense pheromone for ants
• In perfumes for lemon-like scent
• Precursor to vitamin A
CHO
H3C
CH3
CH3
CH3
OH
CH3
Vitamin A
12
The Distillation Experiment: Ch 6
Day Two:
Procedure 3: A microscale distillation of a 50:50 unknown, twocomponent mixture.
Based on the observed boiling point data, determine the identities of the
two components in your unknown mixture. Graph data in Excel. Be sure to
correct the bp’s for the lab’s atmospheric pressure! Adjust bp for pressure:
Add (or subtract) 0.5°C for every 10 Torr the lab’s atmospheric pressure is
below (or above) 760 Torr. Typo in page 164’s sample calculation!!
Also, do solubility tests on each of the purified liquids to confirm
identities.
Possible unknowns: acetone, methanol, hexane, t-butanol, water, toluene,
1-butanol
**Insulate your set-up with glass wool and be sure to use the
correct column (distilling column) from your microscale kit!!!**
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Simple vs. Fractional
Simple Distillation:
• Used to separate mixture into pure components
• Works best if components’ boiling points differ by at least 75°C
Fractional Distillation:
• To be used when components’ boiling points are closer together
• Unlike simple, uses a fractioning column; this column may be
packed with material so as to increase the surface area for heat
exchange, thus increasing the number of theoretical plates.
• The more theoretical plates, the better the purification/separation.
Theoretical Plate: one cycle of vaporization and condensation
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Procedure 4:
1. Adjust bp for pressure:
Add (or subtract) 0.5°C for every
10 Torr the lab’s atom. pressure is
below (or above) 760 Torr.
2. Plot data using
Excel. Be sure to
superimpose both sets of
data on one graph.
Should end up with 2 curves
on one graph.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
3. Compare simple vs.
fractional distillations.
4. Which of the two achieves
the best separation of
liquids?
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Simple vs. Fractional
Prediction:
Fractional distillation is a more effective purification
technique than simple distillation.
An example Excel graph with two data sets superimposed:
A twocomponent
mixture:
A&B
Temperature (°C)
bp of pure B
QuickTime™ and a
TIFF (LZW) decompressor
Simple
are needed to see this picture.
distillation
Fractional distillation
bp of pure A
Drops of Distillate
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