Glyoxylic Acid Chemical Reactions

  • Chemical reactions

Glyoxylic acid (C2H2O3) is a unique organic compound that possesses both an aldehyde and a carboxylic acid functional group. This combination of functional groups makes glyoxylic acid a highly reactive molecule, capable of participating in various chemical reactions. Here are some of the key chemical reactions of glyoxylic acid, along with their mechanisms and reaction equations:

  • Oxidation Reactions

Glyoxylic acid can undergo oxidation reactions, leading to the formation of oxalic acid (C2H2O4) as the final product. This process involves the oxidation of the aldehyde group to a carboxylic acid group.

Mechanism:

The oxidation of glyoxylic acid proceeds through a radical chain mechanism initiated by hydroxyl radicals (OH•) in the presence of molecular oxygen (O2). The aldehyde group is first oxidized to a carboxyl group, forming glyoxylic acid alkyl radical intermediates, which then undergo further oxidation to yield oxalic acid[1].

Reaction equation:

OHC-COOH + OH• + O2 → •OOC-COOH + H2O

  • OOC-COOH + O2 → OOC-COOH + HO2•

OOC-COOH + HO2• → HOOC-COOH + O2

  • Condensation Reactions

Glyoxylic acid can participate in condensation reactions with various nucleophiles, such as alcohols, amines, and phenols, forming esters, amides, and aryl glyoxylates, respectively.

Mechanism:

The condensation reaction proceeds through a nucleophilic addition-elimination mechanism. The nucleophile attacks the electrophilic carbonyl carbon of the aldehyde group, forming a tetrahedral intermediate. Subsequently, a proton is removed, and the leaving group (typically water or an alcohol) departs, forming the condensation product[1, 2].

Reaction equation (with an alcohol):

OHC-COOH + R-OH ⇌ OHC(OR)-COOH ⇌ O=C(OR)-COOH + H2O

  • Reduction Reactions

Glyoxylic acid can undergo reduction reactions, leading to the formation of glycolic acid (C2H4O3). This reaction involves the reduction of the aldehyde group to an alcohol group.

Mechanism:

The reduction of glyoxylic acid can be achieved using various reducing agents, such as sodium borohydride (NaBH4) or hydrogen gas in the presence of a catalyst. The mechanism involves the nucleophilic addition of a hydride ion (H-) to the carbonyl carbon, followed by proton transfer and elimination of water[3].

Reaction equation:

OHC-COOH + 2 H- + 2 H+ → HOCH2-COOH + H2O

  • Decarboxylation Reactions

Glyoxylic acid can undergo decarboxylation reactions, leading to the formation of carbon monoxide (CO) and water (H2O). This reaction involves the removal of the carboxyl group from the molecule.

Mechanism:

The decarboxylation of glyoxylic acid can occur under high temperatures or in the presence of strong acids or bases. The mechanism involves the protonation of the carboxyl group, followed by the elimination of carbon dioxide (CO2) and the formation of a carbonyl compound, which then tautomerizes to the corresponding aldehyde[1].

Reaction equation:

OHC-COOH ⇌ OHC=C(OH)2 → CO2 + OHC-H ⇌ H2O + OHC-H

  • Reactions with Amino Acids (Hopkins-Cole Test)

Glyoxylic acid is used in the Hopkins-Cole test (also known as the Adamkiewicz-Hopkins test) to detect the presence of tryptophan in proteins. In this reaction, glyoxylic acid reacts with the indole group of tryptophan in the presence of concentrated sulfuric acid, forming a purple-colored product[4].

Mechanism:

The mechanism involves the electrophilic addition of glyoxylic acid to the indole ring of tryptophan, followed by oxidation and rearrangement steps to form the colored product.

Reaction equation:

(Tryptophan) + OHC-COOH + H2SO4 → (Purple-colored product)

References

  1. Wei, B., et al., Theoretical study on the aqueous phase oxidation of glyoxal.Environmental Science: Atmospheres, 2023. 3(9): p. 1296-1305.
  2. Mao, H., et al., Effect and Mechanism of Aluminum(III) for Guaiacol–Glyoxylic Acid Condensation Reaction in Vanillin Production.ACS Omega, 2020. 5(38): p. 24526-24536.
  3. drugbank. Glyoxylic acid. Available from: https://go.drugbank.com/drugs/DB04343.
  4. Fearon, W.R., A Study of some Biochemical Tests. No. 2: The Adamkiewicz Protein Reaction. The Mechanism of the Hopkins-Cole Test for Tryptophan. A New Colour Test for Glyoxylic Acid.Biochemical Journal, 1920. 14(5): p. 548.
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