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Experiment
3, page 1
Department
of Chemistry, Imperial College
Third Year Advanced
Practical Organic Chemistry 
EXPERIMENT 3:
THE
PENICILLIN-CEPHALOSPORIN CONVERSION
Aims of the experiment
To use
chromatographic techniques to follow a reaction and to purify
the products.
Techniques used/learned:
Flash
chromatography for small scale purifications; analysis of
complex nmr spectra.
Introduction
The routine
purification of organic compounds, especially in large
quantities, was originally carried out by tedious long column chromatography. Good separations often requires
prolonged elution with solvents of low polarity. Nowadays, the technique of flash
chromatography1has become almost universal for bench-top separations. Flash chromatography involves the
purification of an organic
(or inorganic) compound by partition between a finely divided
stationary phase, usually a
specially manufactured grade of silica gel, and a rapidly
moving organic solvent. The technique is
highly attractive in that separations are rapid (10-20 min is
possible), resolution of similar compounds is often excellent, and the technique
resonably inexpensive. In
many cases reasonably
unstable compounds, such as diazoketones, can be purified
easily by this technique. The choice of
eluant is easily found by prior testing by thin layer
chromatography (t.l.c.).
In this
experiment, the rearrangement2of the penicillin 1to the cephalosporin 2isconveniently
followed by t.l.c. and the
product isolated by flash chromatography.
O
O 
12CO2CHPh2