Electrochemical and Isotopic Investigation of 13C-Enriched Oxalic Acid Facilitated with a Vacuum Electrochemical Reactor

Abstract

The electrolytic decomposition of 13C-enriched oxalic acid was investigated. Oxalic acid and oxalic acid-13C2 were pre-purified by vacuum sublimation and characterized by assay, melting range, and FTIR. An Integrated Vacuum Electrochemical Reactor (IVER) was employed to convert aqueous-phase oxalic acid to CO2 for the 13C-enrichment determinations: oxalic acid solvation, vacuum degas, electrolysis, and mass spectrometric analysis. Highly enriched oxalic acid-13C2 was electrolyzed at 1.5-VDC and the CO2 determined to be 99.5 atom%-13C. Blends of H2C2O4 and H213C2O4 were prepared from 50.5 to 99.5 atom%-13C, dissolved in water, and electrolyzed. For each blend solution, the [12C/13C] isotope separative effect was observed as increases in the (CO2) 13C-enrichment when the aqueous-phase was repeatedly electrolyzed. Furthermore, 50 atom%-13C oxalic acid was electrolyzed while the IVER current was monitored, and thereby the electrolytic isotope separation factor α[12C/13C] is estimated to be 1.03 ± 0.01, at 295 K on platinum. Cyclic voltammograms of 0.10-mole% oxalic acid in water displayed an irreversible oxidation peak at E = +0.95 volt (oxalic acid) and another oxidation peak at E ≥+1.6 volt (water). Cyclic voltammograms of oxalic acid in EMI+BETI− indicate that H2C2O4 can also be oxidized in liquid salts (voltammetric window ∼ 1.4 volt versus Ag/AgCl).