Abstract:
On the basis of a model reaction (electrochemical addition of alpha, beta-unsaturated esters to allyl halides) computer-controlled combinatorial electrosynthesis in an ionic liquid was tested.
At first the ionic liquid butylmethylimidazolium tetrafluoroborate ([BMIM]BF4) was synthesized, purified und tested for its electrochemical properties.
In a second step, the model reaction was reproduced with diethyl fumarate and allyl bromide on the mg-scale in a conventional solvent (DMF). Afterwards, the electrolysis was carried out with a reduced reaction volume in the ionic liquid with diethyl fumarate, methyl crotonate, allyl bromide and 3,3-dimethylallyl bromide, in which three of the four expected products could be analyzed.
Finally, eight different esters were combined with six different allyl halides for reaction in the wells of a microtiter plate. Again, [BMIM]BF4 was used as the electrolyte. With the aid of an SECM-based instrument an electrode bundle was moved into and between the wells, in which the electrolyses took place. In 17 wells the expected products could be detected via GC-MS. In the other cases, the reduced or missing reactivity could be explained on the basis of the reaction mechanism and thereby the mechanistic assumptions could be verified.
The applied SECM-based instrument in combination with ionic liquids is adequate for the combinatorial screening of electrosynthesis reactions.