Oxalic acid

Athanor · official

C₂H₂O₄ · 90.03 g/mol

Also called ethanedioic acid

Reagents

Open in Athanor

Drawn from its SMILES with RDKit

WarningHarmful if swallowed · Harmful in contact with skin

Names and identifiers

IUPAC name: oxalic acid
Synonyms: ethanedioic acid, Aktisal, Aquisal
+ 35 more
Oxiric acid, Kyselina stavelova, Oxaalzuur, Oxalsaeure, Acidum oxalicum, Acide oxalique, Acido ossalico, Ethanedionic acid, NCI-C55209, Ethane-1,2-dioic acid, DTXSID0025816, NSC-62774, Oxalic acid, anhydrous, 9E7R5L6H31, DTXCID805816, CHEBI:16995, Acid, Oxalic, hydron;oxalate, 2-oxo-2-oxonioacetate, Oxalic acid (aqueous), Oxalate, Ferric, Oxalate, Sodium, Oxalate, Iron, Oxalate, Aluminum, Oxalate, Chromium, Oxalate, Disodium, Oxalate, Dilithium, Oxalate, Magnesium, Oxalate, Potassium, Oxalate, Diammonium, Oxalate, Monosodium, Oxalate, Dipotassium, Oxalate, Monoammonium, Oxalate, Monopotassium, RefChem:6477
Molecular formula: C₂H₂O₄
Empirical formula: CHO₂
Molecular weight: 90.03 g/mol
Exact mass: 89.99531
CAS number: 144-62-7
PubChem CID: 971
Canonical SMILES: C(=O)(C(=O)O)O
Isomeric SMILES: C(=O)(C(=O)O)O
InChI: InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)
InChIKey: MUBZPKHOEPUJKR-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Colorless powder or granular solid [Note: The anhydrous form (COOH)2 is a white powder].[6]
6 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– Oxalic acid is an odorless white solid. Sinks and mixes with water. (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– Dry Powder; Other Solid; Large Crystals; CBI; Liquid; Liquid; Other Solid [2] EPA Chemical Data Reporting (CDR)
– HYGROSCOPIC COLOURLESS CRYSTALS OR WHITE POWDER. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– Colorless, odorless powder or granular solid. [4] Occupational Safety and Health Administration (OSHA)
– Colorless, odorless powder or granular solid. [Note: The anhydrous form (COOH)2 is an odorless, white solid.] [5] The National Institute for Occupational Safety and Health (NIOSH)
–shown Colorless powder or granular solid [Note: The anhydrous form (COOH)2 is a white powder]. [6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 94-116. Washington, D.C.: U.S. Government Printing Office, June 1994., p. 238
Odor: Odorless.[6]
Melting point: 189.5 °C[3]
4 values
3 of 4 sources agree on it (most common value).
Value As written Source
189 °C 372 °F (Decomposes) (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
189.5 °Cshown 189.5 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
189 °C 372 °F [4] Occupational Safety and Health Administration (OSHA)
102 °C 215 °F (Sublimes) [5] The National Institute for Occupational Safety and Health (NIOSH)
Boiling point: Reported, but no value passed the checks.
The value and why
Sublimes (NIOSH, 2024) (could not be read; source [1])
Density: 1.90[5]
5 values
5 of 5 sources agree on it (most common value).
Value As written Source
– 1.9 at 59 °F (USCG, 1999) - Denser than water [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– 1.9 g/cm³ [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 1.90 [4] Occupational Safety and Health Administration (OSHA)
– 1.9 @ 17°C [7] PAC Chemical Database, U.S. Department of Energy
–shown 1.90 [5] The National Institute for Occupational Safety and Health (NIOSH)
Solubility in water: Solubility in water, g/100ml at 20 °C: 9-10 (moderate)[3]
4 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– 50 to 100 mg/mL at 75 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
– Water solubility of 220,000 mg/l at 25 °C [6] Hazardous Substances Data Bank (HSDB)cites Yalkowsky SH et al; Arizona Data Base of Water Solubility (1989)
–shown Solubility in water, g/100ml at 20 °C: 9-10 (moderate) [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 14% [5] The National Institute for Occupational Safety and Health (NIOSH)
log P: -0.81[3]
pKa: pKa 1: 1.46[6]
2 values
Only one source reports it.
Value As written Source
–shown pKa 1: 1.46 [6] Hazardous Substances Data Bank (HSDB)cites Clayton, G. D. and F. E. Clayton (eds.). Patty's Industrial Hygiene and Toxicology: Volume 2A, 2B, 2C: Toxicology. 3rd ed. New York: John Wiley Sons, 1981-1982., p. 4936
– pKa 2: 4.40 [6] Hazardous Substances Data Bank (HSDB)cites Clayton, G. D. and F. E. Clayton (eds.). Patty's Industrial Hygiene and Toxicology: Volume 2A, 2B, 2C: Toxicology. 3rd ed. New York: John Wiley Sons, 1981-1982., p. 4936
Vapor pressure: 0.54 [mmHg] @105 °C[7]
2 values
Sources disagree; from PAC Chemical Database, U.S. Department of Energy, the most authoritative.
Value As written Source
0.001 mmHg 0.001 mmHg at 68 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
0.54 mmHgshown 0.54 [mm Hg] @105 °C [7] PAC Chemical Database, U.S. Department of Energy
3 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Autoignition temperature: Reported, but no value passed the checks.
The value and why
Not flammable (USCG, 1999) (could not be read; source [1])

Value	As written	Source
–	Oxalic acid is an odorless white solid. Sinks and mixes with water. (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	Dry Powder; Other Solid; Large Crystals; CBI; Liquid; Liquid; Other Solid	[2] EPA Chemical Data Reporting (CDR)
–	HYGROSCOPIC COLOURLESS CRYSTALS OR WHITE POWDER.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	Colorless, odorless powder or granular solid.	[4] Occupational Safety and Health Administration (OSHA)
–	Colorless, odorless powder or granular solid. [Note: The anhydrous form (COOH)2 is an odorless, white solid.]	[5] The National Institute for Occupational Safety and Health (NIOSH)
–shown	Colorless powder or granular solid [Note: The anhydrous form (COOH)2 is a white powder].	[6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 94-116. Washington, D.C.: U.S. Government Printing Office, June 1994., p. 238

Value	As written	Source
189 °C	372 °F (Decomposes) (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
189.5 °Cshown	189.5 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
189 °C	372 °F	[4] Occupational Safety and Health Administration (OSHA)
102 °C	215 °F (Sublimes)	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	1.9 at 59 °F (USCG, 1999) - Denser than water	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	1.9 g/cm³	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	1.90	[4] Occupational Safety and Health Administration (OSHA)
–	1.9 @ 17°C	[7] PAC Chemical Database, U.S. Department of Energy
–shown	1.90	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	50 to 100 mg/mL at 75 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–	Water solubility of 220,000 mg/l at 25 °C	[6] Hazardous Substances Data Bank (HSDB)cites Yalkowsky SH et al; Arizona Data Base of Water Solubility (1989)
–shown	Solubility in water, g/100ml at 20 °C: 9-10 (moderate)	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	14%	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–shown	pKa 1: 1.46	[6] Hazardous Substances Data Bank (HSDB)cites Clayton, G. D. and F. E. Clayton (eds.). Patty's Industrial Hygiene and Toxicology: Volume 2A, 2B, 2C: Toxicology. 3rd ed. New York: John Wiley Sons, 1981-1982., p. 4936
–	pKa 2: 4.40	[6] Hazardous Substances Data Bank (HSDB)cites Clayton, G. D. and F. E. Clayton (eds.). Patty's Industrial Hygiene and Toxicology: Volume 2A, 2B, 2C: Toxicology. 3rd ed. New York: John Wiley Sons, 1981-1982., p. 4936

Value	As written	Source
0.001 mmHg	0.001 mmHg at 68 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
0.54 mmHgshown	0.54 [mm Hg] @105 °C	[7] PAC Chemical Database, U.S. Department of Energy

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 6
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 2
H-bond acceptors: 2 computed here · PubChem 4
Rotatable bonds: 0 computed here · PubChem 1
TPSA (Å²): 74.6
Formal charge: 0
XLogP3: -0.3 PubChem
Complexity: 71 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C2h of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C26.68%
H2.24%
O71.08%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: -0.84 Crippen (Wildman and Crippen 1999)
log S (water solubility): 0.13 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 1.69 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 90.03
log P ≤ 5 (Crippen): -0.84
H-bond donors ≤ 5: 2
H-bond acceptors ≤ 10: 2

Passes all four rules.

¹³C NMR shifts, predicted

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Warning

Harmonized EU classification (CLP Annex VI). Source [8].

Harmful or irritant

NFPA 704[6]

H302Harmful if swallowed
H312Harmful in contact with skin

Precautionary statements: P264, P270, P280, P301+P317, P302+P352, P317, P321, P330, P362+P364, P501

View all classifications (3)

[8] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · WarningH302, H312
[9] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 0.2% (2 of 1282) of reports.
[9] European Chemicals Agency (ECHA) · 1,282 reports · DangerH302, H312, H318

Exposure limits

PEL-TWA (8-Hour Time Weighted Average): 1 mg/m³[4]
PEL: TWA 1 mg/m3 See Appendix G[5]
REL-STEL (Short Term Exposure Limit): 2 mg/m³[4]
REL: TWA 1 mg/m3 ST 2 mg/m3[5]
TLV: 1 mg/m[3]
TLV-TWA (Time Weighted Average): 1 mg/m³ [2014][4]

First aid

Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]
(General first aid procedures) Eye: Irrigate immediately - If this chemical contacts the eyes, immediately wash (irrigate) the eyes with large amounts of water, occasionally lifting the lower and upper lids. Get medical attention immediately. Skin: Water flush promptly - If this chemical contacts the skin, flush the contaminated skin with water promptly. If this chemical penetrates the clothing, immediately remove the clothing and flush the skin with water promptly.[5]
Fresh air, rest. Half-upright position. Refer immediately for medical attention.[3]
Remove contaminated clothes. Rinse skin with plenty of water or shower for at least 15 minutes. Refer for medical attention .[3]

Storage

Separated from strong oxidants and food and feedstuffs. Dry. Well closed.[3]
Store IN COOL, DRY, well-ventilated location. (oxalic ACID dihydrate)[6]

Incompatibilities

Reacts with strong alkalies, strong oxidizing materials, chlorites, and hypochlorites. (oxalic acid dihydrate)[6]
Strong oxidizers, silver compounds, strong alkalis, chlorites [Note: Gives off water of crystallization at 215 degrees F and begins to sublime].[6]
Strong oxidizers, silver compounds, strong alkalis, chlorites [Note: Gives off water of crystallization at 102 °C (215 °F) and begins to sublime.][5]

Safety data sheets on the supplier’s page: ChemoSapiens, Thermo Fisher Scientific, AKos Consulting & Solutions.

Always read the supplier’s safety data sheet before working with it.

Spectra

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
[3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[4]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
[5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
[6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[7]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
[8]Regulation (EC) No 1272/2008 of the European Parliament and of the Council · EU reuse policy, CC BY 4.0 · via PubChem · retrieved 2026-10-14
[9]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[10]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
[11]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[12]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
[13]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
[14]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[15]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.