Glyoxylic acid

Glyoxylic acid

Names
IUPAC name oxoethanoic acid
Other names formylformic acid; oxoethanoic acid
Identifiers
CAS Number	298-12-4 Y
ChEBI	CHEBI:16891 Y
ChEMBL	ChEMBL1162545 Y
ChemSpider	740 Y
DrugBank	DB04343 Y
Jmol 3D model	Interactive image
KEGG	C00048 Y
PubChem	760
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
SMILES C(=O)C(=O)O
Properties
Chemical formula	C2H2O3
Molar mass	74.04 g·mol−1
Density	1.384 g/mL
Melting point	80 °C (176 °F; 353 K)
Boiling point	111 °C (232 °F; 384 K)
Acidity (pKa)	3.18, 3.32
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
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: Henry's law constant of glyoxylic acid is K_H = 1.09 × 10⁴ × exp[(40.0 × 10³/R) × (1/T − 1/298)].

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

Occurrences and Preparations

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, fungi, and plants to convert fatty acids into carbohydrates. Glyoxylate is the byproduct of the amidation process in biosynthesis of several amidated peptides.

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.

Historically glyoxylic acid was prepared from oxalic acid electrosynthetically:

In organic synthesis, lead dioxide anodes were applied for the production of glyoxylic acid from oxalic acid in a sulfuric acid electrolyte.

Reactions and uses

Glyoxylic acid is about 10x stronger acid than acetic acid, with an acid dissociation constant of 4.7 × 10⁻⁴ (pK_a = 3.32):

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

With base, glyoxylic acid disproportionates:

2 OCHCOOH + H₂O → HOCH₂COOH + HOOC–COOH

Even though the aldehyde is a very minor component of its solutions (as with formaldehyde solutions), glyoxylic acid behaves as an aldehyde in its reactions (again like formaldehyde). 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.

Hopkins Cole reaction

Glyoxylic acid is one of the chemicals used in the Hopkins Cole reaction, used to check for the presence of tryptophan in proteins.

Safety

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