TEMPO-Mediated Paired Electrosynthesis of Ethylene Glycol from Formaldehyde and Methanol at High Current Densities

Herein, a paired electrosynthesis of ethylene glycol from formaldehyde and methanol facilitated by TEMPO is reported. The use of TEMPO accentuates formaldehyde production at the anode, providing additional formaldehyde into the cathodic coupling process. The reaction is performed in water/methanol solution in a simple undivided cell using sulfuric acid-treated graphite electrodes with industrially feasible current densities between 300 and 350 mA cm^-2. Other components of the reaction are sodium chloride which is used as a supporting electrolyte and tributylmethylammonium chloride which raises the current efficiency. With a slight modification in the reaction temperature and current density, the outcome can be tuned from high current efficiency toward higher chemical yields. The conditions of the batch reaction are successfully transferred to a continuous flow-cell arrangement. Mechanistic studies indicate the involvement of hydroxymethyl radicals in the electrolysis, and deuterium-labeling experiments show the partial conversion of methanol into formaldehyde and ethylene glycol.