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Experiment 3, page 1

IMAGE imgs/3-penicillin01.gif Department of Chemistry, Imperial College
Third Year Advanced Practical Organic Chemistry IMAGE imgs/3-penicillin02.gif IMAGE imgs/3-penicillin01.gif


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.

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 chromatography
1has 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.

IMAGE imgs/3-penicillin04.gif O IMAGE imgs/3-penicillin05.gif IMAGE imgs/3-penicillin04.gif O IMAGE imgs/3-penicillin07.gif