Study on Synthesis of Glycine by Electrooxidation of Ethanolamine

doi:10.6023/cjoc202502009

Abstract

The aim of this study was to synthesize glycine (Gly) by electrooxidation of ethanolamine (MEA). The influence of electrolyzer structure on the reaction was studied. Comparing the results of membrane-free and membrane electrolyzers revealed that the membrane-free electrolyzer performed better Gly yield, Gly selectivity, MEA conversion, and current efficiency. Through a series of experiments, it was found that the main reason for the higher performance of membrane-free electrolyzer was the occurrence of dissolving part of Pb(II) species from the cathode Pb surface. The dissolved Pb(II) migrated to the anode, oxidized and attached on the surface of the anode to generate PbO₂, The synergistic effect of PbO₂ and Pt promoted the oxidation of MEA and the yield of glycine. Electrochemical in-situ infrared spectroscopy study was applied to investigate the effect of Pt-PbO₂ and revealed that the adsorbtion of C—OH, the oxidatin of C—OH and C=O bond were promoted on Pt-PbO₂ electrode. Finally, by optimizing the electrolyte type and concentration, ethanolamine concentration, and current density, glycine was obtained in a high yield of 90.54%, along with a glycine selectivity and an ethanolamine conversion of more than 90%. The electrooxidation reaction is repeatable, and 88% MEA can be collected from the electrolyte.

Key words: ethanolamine electrooxidation, glycine, electrolytic cell structure screening, electrooxidation mechanism, optimal electrolysis conditions

Cite this article

Ying Li, Shuozhen Hu, Wei Fang, Xing Xiao, Xinsheng Zhang. Study on Synthesis of Glycine by Electrooxidation of Ethanolamine[J]. Chinese Journal of Organic Chemistry, 2025, 45(10): 3873-3884.

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Fig. & Tab. 15

Figure 1. Influence of electrolyzer type on Gly yield, Gly selectivity, MEA conversion, and Faraday efficiency

Figure 2. Comparison of glycine content before and after exchanging the anode-cathode

Scheme 1. Reaction pathways of electro-oxidation of ethanolamine

Figure 3. (a) Comparison diagram of the Pt anode before and after undivided electrolysis with lead as the cathode; (b) SEM image of the Pt electrode before undivided electrolysis and (c) SEM image of the Pt electrode after undivided electrolysis; (d) XRD patterns of the Pt electrode before and after undivided electrolysis

Figure 4. Comparison of Gly yield (a), Gly selectivity (b), and MEA conversion (c), in a diaphragm electrolysis, Pt (black) and Pt-PbO2 (red) as anodes with Pb as cathode

Scheme 2. Schematic diagram of the experiment to investigate the effect of cathode dissolution on the electrolysis efficiency

Anode	Gly yield/%	Gly selectivity/%	MEA conversion/%	Faraday efficiency/%
Pt	27.02	45.40	59.52	21.62
PbO₂	70.28	78.50	89.54	56.25
Pt-PbO₂	80.99	81.45	99.43	64.81

Table 1. Influence of Pt, PbO2 and Pt-PbO2 on the yield of Gly, selectivity of Gly, MEA conversion, and Faraday efficiency

Figure 5. In-situ multi-step staircase infrared spectroscopy of Pt electrode (a, b) and Pt-PbO2 electrode (c, d) in 0.3 mol/L MEA＋2.0 mol/L H2SO4 solution at the research potential of 1.9~3.0 V (vs. Ag/AgCl) (b and d are the enlarged view of Figures a and c)

Figure 6. Time-resolved in situ infrared spectra of Pt electrode (a) and Pt-PbO2 electrode (b) in 0.3 mol/L MEA＋2.0 mol/L H2SO4 solution at 2.4 V (vs. Ag/AgCl)

Acid-base environment	Gly yield/%	Gly selecti- vity/%	MEA con- version/%
Acidic media	79.22	88.61	89.40
Alkaline media	3.09	5.25	58.99

Table 2. Effect of acid-base environment on MEA electrosynthesis of Gly

Figure 7. Effect of acid type on MEA conversion, Gly yield, and selectivity

Figure 8. Effect of sulfuric acid concentration on the yield of Gly (a), and current efficiency, Gly selectivity, and MEA conversion (b)

Figure 9. Effect of ethanolamine concentration on the yield of Gly (a), current efficiency, Gly selectivity, and MEA conversion (b)

Figure 10. Effect of current density on the yield of Gly (a), and Gly selectivity, MEA conversion, and current efficiency (b)

Serial number	Gly yield/%	Gly selecti- vity/%	MEA con- version/%	Faraday efficiency/%
1	84.23	88.03	95.69	67.28
2	86.30	90.16	95.73	69.53
3	85.57	88.43	96.77	68.50

Table 3. Electrolysis reaction repeatability test results.

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