Glyoxylic acid

Glyoxylic acid
IUPAC name oxoethanoic acid
Other names formylformic acid; oxoethanoic acid
Identifiers
CAS number	298-12-4 Y
PubChem	760
ChemSpider	740 Y
DrugBank	DB04343
KEGG	C00048 Y
ChEBI	CHEBI:16891 Y
ChEMBL	CHEMBL1162545 Y
Jmol-3D images	Image 1
SMILES C(=O)C(=O)O
InChI InChI=1S/C2H2O3/c3-1-2(4)5/h1H,(H,4,5) Y Key: HHLFWLYXYJOTON-UHFFFAOYSA-N Y InChI=1/C2H2O3/c3-1-2(4)5/h1H,(H,4,5) Key: HHLFWLYXYJOTON-UHFFFAOYAU
Properties
Molecular formula	C2H2O3
Molar mass	74.04 g mol−1
Melting point	80 °C[1]
Boiling point	111 °C
Related compounds
Other anions	glyoxylate
Related carboxylic acids	formic acid acetic acid glycolic acid oxalic acid propionic acid pyruvic acid
Related compounds	acetaldehyde glyoxal glycolaldehyde
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Glyoxylic acid or oxoacetic acid is an organic compound. Together with acetic acid, glycolic acid, and oxalic acid, glyoxylic acid is one of the C₂ carboxylic acids. It is a colourless solid that occurs naturally and is useful industrially.

Structure and nomenclature

Glyoxylic acid is usually described with the chemical formula OCHCO₂H, i.e. containing an aldehyde functional group (see image in upper right). In fact the aldehyde is not observed in solution or as a solid. In general aldehydes with electron-withdrawing substituents often exist mainly as their hydrate. Thus, the formula for glyoxylic acid is really (HO)₂CHCO₂H, described as the "monohydrate." This diol exists in equilibrium with the dimeric hemiacetal in solution:^[2]

2 (HO)₂CHCO₂H $\overrightarrow{\leftarrow}$ O[(HO)CHCO₂H]₂ + H₂O

Preparation

The compound is formed by organic oxidation of glyoxal with hot nitric acid, the main side product being oxalic acid. Ozonolysis of maleic acid is also effective.^[2]

The conjugate base of gloxylic acid is known as glyoxylate and is the form that the compound exists in solution at neutral pH. Glyoxylate is an intermediate of the glyoxylate cycle, which enables organisms, such as bacteria, ^[3] fungi, and plants ^[4] to convert fatty acids into carbohydrates. Glyoxylate is the byproduct of the amidation process in biosynthesis of several amidated peptides.

Reactions and uses

Glyoxylic acid is about 10x stronger acid than acetic acid, with an acid dissociation constant of 4.7 × 10⁻⁴:

(HO)₂CHCOOH $\overrightarrow{\leftarrow}$ (HO)₂CHCO₂⁻ + H⁺

With base, glyoxylic acid disproportionates:

2 OCHCOOH + H₂O → HOCHCOOH + HOOC–COOH

Even though the aldehyde is a very minor component of its solutions, glyoxylic acid behaves as an aldehyde in its reactions. For example, it gives heterocycles upon condensation with urea and 1,2-diaminobenzene.

Phenol derivatives

Its condensation with phenols is versatile. The immediate product is 4-hydroxymandelic acid. This species reacts with ammonia to give hydroxyphenylglycine, a precursor to the drug amoxicillin. Reduction of the 4-hydroxymandelic acid gives 4-hydroxyphenylacetic acid, a precursor to the drug atenolol. Condensations with guaiacol in place of phenol provides a route to vanillin, a net formylation.^[2]

Safety

The compound is not very toxic with an LD₅₀ for rats of 2500 mg/kg.

References

1. ^ Merck Index, 11th Edition, 4394
2. ^ ^{a b c} Georges Mattioda and Yani Christidis “Glyoxylic Acid” Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_495
3. ^ Holms WH (1987). "Control of flux through the citric acid cycle and the glyoxylate bypass in Escherichia coli". Biochem Soc Symp. 54: 17–31. PMID 3332993. 
4. ^ Escher CL, Widmer F (1997). "Lipid mobilization and gluconeogenesis in plants: do glyoxylate cycle enzyme activities constitute a real cycle? A hypothesis". Biol Chem. 378 (8): 803–813. PMID 9377475.