Electrosynthesis of Squaric Acid under Low CO Pressure

Abstract

Electrosynthesis of squaric acid was accomplished under low CO pressure (ca. 10 kgf cm⁻²). CO was reduced to squarium ions in an electrolyte consisting of THF-DMF mixture with 0.1 M tetra-n-butylammonium bromide. Current efficiencies for squaric acid formation were examined at Fe, Zn, Al, Ti, Ni and stainless steel (SUS304, SUS316, SUS321, SUS347 and SUS430). The current efficiency for squaric acid formation is about 45% at less than 15 mA cm⁻² at SUS430 cathode, and decreases at more than 10 mA cm⁻² at Mg anode. The formation of squarium ions needs at least 10 kgf cm⁻² CO pressure. Squarium ions are hardly formed in an electrolyte containing 1% water.