An activity scale of cathode materials for the electrochemical cyclisation of allyl 2-bromobenzyl ether

Abstract

The electrocatalytic activity of 10 cathode materials (Ag, Au, Cu, Glassy carbon (GC), Ni, Mg, Mn, Pb, Pt and Ti) was examined for the intramolecular cyclisation reaction of allyl 2-bromobenzyl ether to 2-methyl benzopyran. The influence of the cathode materials on the electrocatalytic activity was tested by means of cyclic voltammetry (CV) in an electrolyte solution of allyl 2-bromobenzyl ether (1mM) + tetrabutylammonium perchlorate (0.1M) (Bu4NClO4) in methanol (MeOH). On Au, GC, Ni, Mg, Mn, Pb and Pt one single reduction wave was measured while Ag and Cu exhibited two cathodic reduction waves. Ti did not show a voltammetric response. The best electrocatalytic activity was obtained on Ag which showed a shift of the reduction peak potential of 771mV with respect to GC, the most inert material. In addition to the screening, rotating disk experiments (RDE) in combination with Koutecky Levich analysis and product formation during electrosynthesis were performed. Koutecky Levich analysis of the RDE at peak potential showed that one-electron was transferred at Au, GC, Ni, Mg, Mn, Pb and Pt. On Ag and Cu the number of transferred electrons determined with Koutecky-Levich depends on the potential and can be tuned to specific one- or two-electron transfer. Electrosynthesis showed that on Au, GC, Ni, Mg, Mn, Pb and Pt exclusively 5-methyl benzopyran was formed. On Ag and Cu product formation was depended on the potential and 2-methyl benzopyran and allyl benzyl ether (not cyclized product) were both formed.