Electrolyte free electro-organic synthesis: The cathodic dimerisation of 4-nitrobenzylbromide in a micro-gap flow cell

The electrochemical reduction of 4-nitrobenzylbromide is studied in N,N-dimethylformamide solution in the presence and in the absence of intentionally added supporting electrolyte. By conventional voltammetry it is shown that an ECE-type reaction occurs with formation of the dimer 4,4′-dinitrodibenzyl irrespective of the presence of supporting electrolyte. Next, a micro-gap flow cell is characterised and employed for the preparative electro-reduction in the absence of supporting electrolyte. Excellent yields of the dimer are obtained and explained based on a self-propagation mechanism.