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Experiment
3, page 4
Spillage & disposal:Clear area, shut off all sources
of ignition. Wear goggles, gloves, and laboratory coat.
Mop up with plenty of water and run to waste.
Organise effective
ventilation and
evaporate residual liquid.
Experimental Procedure
Preliminaries
1.Obtain dioxane (pre-dried over
sodium, 20ml) from the bottle provided(DO NOT
ATTEMPT TO DRY THE SOLVENT
WITH SODIUM YOURSELF!!!) in a
pre-dried flask.
2.Establish a t.l.c.
system for the b-lactam ester 1to give an Rfvalue between 0.2 and
0.3. Use a mixtures of ethyl acetate and
dichloromethane. The spots can be visualised
under the u.v. lamp and by placing the plates in a
jar containing a few crystals of
iodine.
3.Record and interpret the i.r. spectrum of the
penicillin; interpret the nmr spectrum of
the penicillin (provided).
Rearrangement of Penicillin V
b-Sulphoxide 1.
In a 25ml round
bottomed 2 or 3 necked flask,
dissolve dry pyridine (10ml) and 85% orthophosphoric acid (14ml) in dry redistilled
dioxan (see above) (10ml). Measure the acid and base using a Gilson micropipette with a new
tipfor each
reagent. Add the penicillin ester 1(0.50g) as provided, and heat the mixture to reflux
overnight under nitrogen (CARE: check all
joints). Before commencing heating, flush the flask with
N2and
subsequently maintain a slight positive pressure of
N2applied to the
top of the condenser, viaa T-piece with a liquid paraffin bubbler (see
Demonstrator / Technician for details). Do notpurge the system continuously with
N2since this
will evaporate the solvent.
Allow the solution to cool. Recheck the t.l.c. If necessary, adjust the solvent
composition (to x% EtOAc/DCM) to give an RFof [!]0.5 for the
product.
Flash Chromatography and Isolation of the
Product
IMPORTANT!!!! SAFETY NOTE: Silica gel is dangerous by inhalation.
Handle the dry silica in a fume hood. Once
slurried, the material can be used on the bench provided
it is not allowed to run
dry. Dispose of all silica residues in the bin
provided.
Cover
the sintered glass column with the plastic safety webbing
provided and clamp it vertically over a conical flask. IN A FUME HOOD, slurry BDH flash
chromatography silica(12g)
in a conical flask with
dichloromethane (DCM). Pour the slurry into the column and wash
in the residue with more
DCM. Using the hand
bellows, force the DCM through the column and thus compact the silica. It is essential
that the level of solvent is not forced beyond the top of the
silica otherwise channels
will form in the silica and its effectiveness destroyed.
The surface of the silica
pad mustbe as flat as possible. With
extreme care, add more DCM to the column; do not disturb
the silica surface. Pouring
the solvent carefully down the side of the column over the
blade of a wide spatula is
helpful. Again, force the solvent through the column so that
the surface of the silica
is just damp with DCM. If cracking or channelling occurs,
repack the column..
Evaporate the dioxan solution containing the product to
complete dryness. dissolve the residue in the minimumvolume of DCM and carefully apply
dropwise to the surface of the silica. Wash on the last traces with a further small volume of DCM.
Using the bellows,
carefully force the liquid
onto the column so that the level of liquid is again just flush
with the silica surface. Rinse the edges