Experiment 11 ISOLATION OF CAFFEINE FROM TEA

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Experiment 11ISOLATION OF CAFFEINE FROM TEA

• Reading Assignment
• pp. 119 127
• Technique 7, pp. 595 613
• Green Lab people download materials
• Technique 16, pp. 726 - 731

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Caffeine
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Distribution Coefficient
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See page 597 for an example on how this equation
is applied to extraction.
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Bottom line! You will
remove more solute (caffeine) from an aqueous
solution by using two 1 mL portions of methylene
chloride than by using one 2 mL portion of
methylene chloride! See the textbook for an
example.
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Separatory funnel
Remove from top before you start to drain!
Remember! Close stopcock before pouring stuff in
the top of the funnel!
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Which layer on the top?Which layer is on the
bottom?
You need to know the density of the methylene
chloride and the density of the aqueous phase to
answer this question!
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Green extraction of caffeine from tea
You will remove caffeine from tea using a Solid
Phase Extraction column (SPE). Be sure to
download the experiment and some of the
technique materials from Charles Wandlers web
page.
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Solid Phase Extraction (SPE)
SPE column filled with C-18 silica
Two Neoprene adapters
To house vacuum
Filter flask
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C-18 silica
Silica is alkylated with long chain hydrocarbon
groups, using 18 carbons long. This is usually
referred to as C-18 silica.
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Solid phase extraction (SPE)

• The C-18 column packing is NON-POLAR
• Caffeine will move more slowly because it is
  attracted to the column packing.
• The more polar components such as tannins, gallic
  acid and chlorophyll move more quickly down the
  column with the the polar water
• Once the aqueous materials have moved down the
  column, then you elute the caffeine with ethyl
  acetate.

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Sublimation Behavior
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Sublimation Apparatus
To house vacuum
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• Three examples
• A solid will melt if its vapor pressure is below
  the
• applied pressure when the solid is heated to
  its
• melting point.
• 2. A solid will sublime if its vapor pressure is
  higher than
• the applied pressure as it is heated. You
  will not
• observe melting behavior.
• If you want to sublime a solid that has a vapor
• pressure of 50 mm Hg, you can do this if you
  reduce
• the pressure, under vacuum, to below this
  value.

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MIDTERM EXAMINATION

• Friday, February 10th
• 200 to 250 PM
• Distillation lab (Exp 6) is due Monday
• or Tuesday, depending on your section.
• Dr. Pavia will post answers to the questions in
  the post lab on his bulletin board after Tuesday
  so you have them for the test on Friday!

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Coverage

• EXP. 2 SOLUBILITY
• EXP. 3 CRYSTALLIZATION
• EXP. 5 CHROMATOGRAPHY
• EXP. 6 SIMPLE AND FRACTIONAL DISTILLATION
  AND GAS CHROMATOGRAPHY
• ALSO READ
• PP. 1 - 36
• 49 71
• 80 - 93
• TECHNIQUES 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 15

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BRING YOUR CALCULATOR
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Experiment 52PREPARATION OF A C-4 OR C-5 ACETATE
ESTER

• Reading Assignment
• pp. 128 135
• pp. 470 475
• Technique 3, pp. 529 534 536
• Technique 6, pp. 585 595
• Technique 7, pp. 605 611
• Technique 8, pp. 617 629
• Technique 19, pp. 742 760
• Appendix 3, pp. A14 A32
• Appendix 4, pp. A32 A50 (probably not required

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Main Reaction
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Ideal stopping place
There may be some ROH left in the ester
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Why the extraction with NaHCO3?
Ionic substance now soluble in the aqueous phase
Partly soluble In the ester
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Preparation of Esters Gas Chromatography
solvent
Unreacted cyclopentanol
Some Alkene may Appear here
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Preparation of Esters Gas Chromatography
Ret.
Time Width
Peak Peak Result Time Offset
Area Sep. 1/2 Status No. Name
() (min) (min) (counts) Code
(sec) Codes ---- ------------ ----------
------- ------- ---------- ---- ----- ------
1 4.2884 4.943 0.000
10754 BB 1.8 2
95.7116 6.392 0.000 240011 BB 1.4
---- ------------ -------
---- ----- ------
Totals 100.0000 0.000
250765
Total Identified Counts 250765 counts
In some cases, you may observe extra unknown
peaks. Recalculate the percentages of your data
based on the alcohol and ester peaks. Round off
the percentages 4.3 cyclopentanol 95.7
cyclopentyl acetate
Assume that all response factors 1.000
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We will not be using response factors for the
esters Lab (assuming that they are 1.0).
However, you may need to recalculate the data to
give new areas if you have extra peaks that
dont belong. The example data in the previous
slide can be used directly without doing
calculations. The usual products include alkene
from dehydration, unreacted alcohol and ester.
Esters have the longest retention times, alkenes
are lowest and unreacted alcohol is in the
middle someplace! You will also be running the
infrared spectrum of your product.
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Infrared spectroscopy and other material
associated with the esters lab will be covered on
February 17th