Oxalic acid

Oxalic acid
	Oxalic acid dihydrate
Names
	IUPAC name 1,2-ethanedioic acid
	Preferred IUPAC name Oxalic acid
	Systematic IUPAC name Ethanedioic acid
	Other names Wood bleach; (Carboxyl)carboxylic acid; Carboxylformic acid; Dicarboxylic acid; Diformic acid;
Identifiers
CAS Number	144-62-7 (anhydrous) ; 6153-56-6 (dihydrate) ;
3D model (JSmol)	Interactive image;
Beilstein Reference	385686
ChEBI	CHEBI:16995 ;
ChEMBL	ChEMBL146755 ;
ChemSpider	946 ;
DrugBank	DB03902 ;
ECHA InfoCard	100.005.123
EC Number	205-634-3;
Gmelin Reference	2208
KEGG	C00209 ;
MeSH	Oxalic+acid
PubChem CID	971;
RTECS number	RO2450000;
UNII	9E7R5L6H31 ; 0K2L2IJ59O (dihydrate) ;
UN number	3261
CompTox Dashboard (EPA)	DTXSID0025816 ;
	InChI InChI=1S/C6H6O6/c3-1(4)2(5)6/h(H,3,4)(H,5,6) Key: MUBZPKHOEPUJKR-UHFFFAOYSA-N ;
	SMILES OC(=O)C(=O)O;
Properties
Chemical formula	C2H2O4
Molar mass	90.034 g⋅mol−1 (anhydrous); 126.065 g⋅mol−1 (dihydrate);
Appearance	White crystals
Odor	Odorless
Density	1.90 g/cm3 (anhydrous, at 17 °C (63 °F)); 1.653 g/cm3 (dihydrate);
Melting point	189–191 °C (372–376 °F; 462–464 K) (anhydrous); 101.5 °C (214.7 °F; 374.6 K) (dihydrate);
Boiling point	decomposes (see article for details)
Solubility in water	46.9 g/L @ 5 °C (41 °F); 57.2 g/L @ 10 °C (50 °F); 75.5 g/L @ 15 °C (59 °F); 95.5 g/L @ 20 °C (68 °F); 118 g/L @ 25 °C (77 °F); 139 g/L @ 30 °C (86 °F); 178 g/L @ 35 °C (95 °F); 217 g/L @ 40 °C (104 °F); 261 g/L @ 45 °C (113 °F); 315 g/L @ 50 °C (122 °F); 376 g/L @ 55 °C (131 °F); 426 g/L @ 60 °C (140 °F); 548 g/L @ 65 °C (149 °F);
Solubility in ethanol	237 g/L @ 15 °C (59 °F)
Solubility in diethyl ether	14 g/L @ 15 °C (59 °F)
Vapor pressure	2.34×10−4 mmHg @ 20 °C (68 °F); 0.54 mmHg @ 105 °C (221 °F);
Acidity (pKa)	1.25 and 4.28
Conjugate base	Hydrogenoxalate
Magnetic susceptibility (χ)	−60.05×10−6 cm3/mol
Thermochemistry
Heat capacity (C)	91.0 J/(mol·K)
Std molar; entropy (S⦵298)	109.8 J/(mol·K)
Std enthalpy of; formation (ΔfH⦵298)	−829.9 kJ/mol
Pharmacology
ATCvet code	QP53AG03 (WHO)
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Corrosive
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302+H312, H318, H402
Precautionary statements	P264, P270, P273, P280, P301+P312+P330, P302+P352+P312, P305+P351+P338+P310, P362+P364, P501
NFPA 704 (fire diamond)	3 1 0 ACID
Flash point	166 °C (331 °F; 439 K)
	Lethal dose or concentration (LD, LC):
LDLo (lowest published)	1000 mg/kg (dog, oral); 1400 mg/kg (rat); 7500 mg/kg (rat, oral);
	NIOSH (US health exposure limits):NIOSH Pocket Guide to Chemical Hazards. "#0474". National Institute for Occupational Safety and Health (NIOSH).
PEL (Permissible)	TWA 1 mg/m3
REL (Recommended)	TWA 1 mg/m3; ST 2 mg/m3;
IDLH (Immediate danger)	500 mg/m3
Safety data sheet (SDS)	External MSDS
Related compounds
Related compounds	oxalyl chloride; disodium oxalate; calcium oxalate; phenyl oxalate ester;
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula HO−C(=O)−C(=O)−OH, also written as (COOH)₂ or (CO₂H)₂ or H₂C₂O₄. It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name is derived from early investigators who isolated oxalic acid from flowering plants of the genus Oxalis, commonly known as wood-sorrels. It occurs naturally in many foods. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.

Oxalic acid is a much stronger acid than acetic acid. It is a reducing agent and its conjugate bases hydrogen oxalate (HC₂O−4) and oxalate (C₂O2−4) are chelating agents for metal cations. It is used as a cleaning agent, especially for the removal of rust, because it forms a water-soluble ferric iron complex, the ferrioxalate ion. Oxalic acid typically occurs as the dihydrate with the formula H₂C₂O₄·2H₂O.