A "green" synthesis intended for undergraduate organic students.
One way that the scientific community can influence its direction
in the drive for "green" chemistry is to influence young
chemists early in their careers. This experiments initiates that
viewpoint. The experiment is an adaptation of the Mannich reaction,
which is a useful way to form C-C single bonds between two molecules.
The first step is the formation of an imine between p-anisidine and
ethyl glyoxalate using molecular sieve. Once the reaction is complete a
Celite filtration step is performed and the solvent is then removed by
vacuum distillation. The purity of the imine is determined with GC-MS or
IH-NMR. The next step utilizes the pre-generated imine along with
acetone, the ionic liquid [bmim]BF4, and proline, as the catalyst.
Thin-layer chromatography (TLC) is used to monitor the progress of the
reaction. The product must then be extracted and filtered before
analyzing it with GC-MS, 1H-NMR, IR, and polarimetry. There are several
features about this experiment that make it particularly attractive.
First, the use of ionic liquids is a relatively new "green"
technique that has not found its way to textbooks currently used in
organic laboratories. Another feature of the experiment is the
presentation of isotopic labeling by using d6-acetone. The reaction also
includes the facet of stereocenter control through the use of either L-
or D- proline to give either the S or the R version of the product,
respectively. All of these factors, along with the low cost, scale, and
feasibility of the experiment, make it a great learning experience for
the fledgling chemist.
* Kimmell II, C. K., Bennett, J., Meldi, K. Walter J. Hoffman
Department of Chemistry, Drury University.