Betulin Project – Experiment #1: Isolation of Betulin from the Bark of Betula alba
For prelab write-up, follow the format as posted on the lab website for CH 203. State
the purpose of this experiment, show the structure of betulin, then write out the procedure.
All steps of the procedures should be carried out in a hood. Always safety glasses, lab coats,
and gloves. When you are finished, please clean all glassware and replace on the “Betulin
Cart”.
The bark of the white birch (Betula alba, collected in Harvard, MA, Sept 8,
2013) is cut into small pieces (roughly 1 -2 in2), weighed, and placed in a 1L
Erlenmeyer flask, sufficient to fill the flask. Then, dichloromethane (DCM) is
added to cover the bark, and the mixture allowed to stand for approx. 1 hour.
The extract is filtered in vacuo, then the filtrate transferred to a 1L round
bottom flask, The solvent was reduced on a rotary evaporator until abundant
formation of solid matter results. The evaporation was then stopped, and the
precipitate collected by vacuum filtration. After drying in the Buchner funnel,
weigh the crystals, and run TLC (thin layer chromatography) plate, record a
UPLC-MS and an 1H-NMR spectrum. If need be, the betulin can be
recrystallized from methanol/chloroform, 1:1 (MeOH/CHCl3).
When running a TLC, you need to find (1) the best solvent system to develop
your TLC plate, and (2) the best stain to visualize your “spots” on the TLC.
Since betulin is rather non-polar (though with the polar alcohol functional
groups), a good place to start in finding a solvent system for the TLC is
hexanes:ethyl acetate (EtOAc), 10:1. Ideally, the betulin spot will move with
an Rf of about 0.3 – 0.5. If it moves too fast, reduce the polarity of your solvent
system (try 95:5, for example). If it moves to slowly, increase the polarity
(maybe 8:1, for example). You will also have to find a stain to visualize the
spots. Your TF will help you with this process.
Post-lab write-up. Turn in a post-lab write-up that includes the purpose of the experiment,
the procedure, and the calculated yield of betulin from the bark. Also, answer the four
questions posed in the project description.
Objectives/Procedure – Prelab: 20 pts
Purpose – 3 pts
Betulin Structure – 5 pts
Procedure – 12 pts
Observations including yield (wt and %): 45 pts
Written Observations – 10 pts
Yield wt – 5 pts
Cleanliness – 5 pts
Safety – 5 pts
Overall lab performance – 20 pts
Post-lab questions: 35%
% Yield – 5 pts
Question #1 – 5 pts
Question #2 – 10 pts
Question #3 – 10 pts (5 pts each structure)
Question #4 – 5 pts
NOTES:
1) One can get ~200 g of birch bark into the 1000 mL Erlenmeyer. The extraction should
yield 15 – 20 g of betulin overall, though the crystallization that occurs on the rotary
evaporator may only yields ~2 g of betullin. The remaider will eventually crystallize fro
the filtrate, so don't throw this away.
2) The TLC solvent that worked the best was hexanes:EtOAc (5:1).
3) TLC stains that work include: vanillin – switched to ninhydrin and anisaldehyde for last
two labs (oxime and Beckman rearrangement)