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Oxaloacetic acid

Oxaloacetic acid

IUPAC name	Oxobutanedioic acid
Other names	Oxaloacetic acid Oxalacetic acid Oxosuccinic acid
Identifiers
CAS number	328-42-7
EINECS number	206-329-8
SMILES	OC(C(CC(O)=O)=O)=O
Properties
Molecular formula	C₄H₄O₅
Molar mass	132.07 g/mol
Density	? g/cm³
Melting point	161 °C
Thermochemistry
Std enthalpy of formation Δ_fH^o₂₉₈	-943.21 kJ/mol
Std enthalpy of combustion Δ_cH^o₂₉₈	-1205.58 kJ/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Oxaloacetic acid is an organic compound with the chemical formula HO₂CC(O)CH₂CO₂H. It also has other names (see Table) and its conjugate base is called "oxaloacetate." This four-carbon dicarboxylic acid is a protonated variant of oxaloacetate, which is an intermediate of the citric acid cycle and gluconeogenesis. Oxaloacetate forms upon oxidation of L-malate, catalysed by malate dehydrogenase, and reacts with Acetyl-CoA to form citrate, catalysed by citrate synthase. It also forms in the mesophyll of plants by the condensation of CO₂ with phosphoenolpyruvate, catalysed by PEP Carboxykinase. It can arise from pyruvate via an anaplerotic reaction.

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The enol forms of oxaloacetic acid are particularly stable, so much so that the two isomers have different melting points (152 °C cis, 184 °C trans). The enol proton has a pK_a value of 13.02. The enzyme fumarase A from E. coli catalyses the conversion between the keto and enol forms.

Oxaloacetate is unstable in solution, decomposing to pyruvate by decarboxylation over a period of hours (room temperature) or days (0 °C). Refrigerated storage of the solid is therefore recommended.