Today:
1) Infrared Spectroscopy (IR)
2) Introduction to Exp. 10:
Caffeine from Tea Leaves
Infrared Spectroscopy (IR)
1) What is the approximate range of wavelengths
visible to humans? And where would you find
the range of IR light? How about its energy
compared to visible light?
2) What are the "wavenumbers", commonly used in
IR to define absorptions?
3) What type of information do we obtain from an IR
spectrum?
4) How can we identify a compound from its IR, e.g.
how can we know that we obtained eugenol?
5) How will your IR tell you if your eugenol sample
contains impurities?
IR: Study Ch.9, esp. from p.536
Excellent website:
http://www.chem.ucla.edu/~webspectra/index.html
Exp. 10:
Isolation of Caffeine from Tea Leaves
1. Caffeine is an alkaloid. What are “alkaloids”?
Examples of other alkaloids?
2. Do you recognize any functional groups in
caffeine?
3. Caffeine is slightly basic. Which group is
responsible for its basic character?
4. Caffeine is usually found as a salt (citrate,
malate, other) in plants. What could be the
advantage of this for the plant?
1. Caffeine has an LD50 (orally, in mice) of
127mg/kg. What is the LD50?
2. What is the solubility of caffeine a) in cold
water? b) in hot water? c) In room temp.
CH2Cl2?
3. What is the purpose of adding Na2CO3 to
the tea solution at the beginning of the
experiment? (Hint: see 4.)
4. What else is in tea leaves besides
caffeine…?
1. Why do we add anh. Na2SO4 to the CH2Cl2
layer before evaporating?
2. What is a “sublimation” ?
3. Why is it tricky to measure the mp. of caffeine?
Experimental Hints
• Weigh the teabags without the tag and the string. But
do NOT open the tea bags.
• During heating take care not to tear the tea bags.
• During the extraction (in which layer do you expect
caffeine?) emulsions can form:
• Remedies:
– wait a few more minutes for separation of layers to
occur and separate as well as possible
– Add more CH2Cl2
– Fill into centrifuge tubes (two, balance!) and
centrifugate
Caffeine Report Form
Weight of tea bags
Weight of crude caffeine
% of crude caffeine in your tea sample
Weight of sublimed caffeine
What does caffeine look like?
For your report find the approximate caffeine content of
your “favorite” beverages: coffee, tea, coca cola ..
etc.
Next Experiment:
Exp.6: Column Chromatography of Ferrocene
Midterm October 27!
will include Exp. 6 material
Start reviewing lab lectures, practice questions,
experiments. Review calculations, graphs.