Citric acid (C6H8O7): structure, properties and hazards

Names and identifiers

IUPAC name: 2-hydroxypropane-1,2,3-tricarboxylic acid
Synonyms: citrate, E330, TCA cycle
+ 37 more
2-hydroxypropane-1,2,3-tricarboxylic acid, Citric acid, anhydrous, Aciletten, Anhydrous citric acid, Citro, Citretten, Citric acid anhydrous, Chemfill, Hydrocerol A, 1,2,3-Propanetricarboxylic acid, 2-hydroxy-, 2-hydroxy-1,2,3-propanetricarboxylic acid, Kyselina citronova, 2-Hydroxytricarballylic acid, beta-Hydroxytricarballylic acid, 3-Carboxy-3-hydroxypentane-1,5-dioic acid, FEMA No. 2306, FEMA Number 2306, Citric acid,anhydrous, Citricum acidum, Citric acid monoglyceride, Acidum citricum, DTXSID3020332, Citric acid bp, XF417D3PSL, NSC-30279, Citric acid,hydrous, NSC-626579, Citric acid, hydrous, NSC30279, NSC-112226, DTXCID50332, 2-hydroxy-1,2,3-propanetricarboxyic acid, INS NO.330, CHEBI:30769, INS-330, B1650, E-330
Molecular formula: C₆H₈O₇
Empirical formula: C₆H₈O₇
Molecular weight: 192.12 g/mol
Exact mass: 192.02700
CAS number: 77-92-9
PubChem CID: 311
Canonical SMILES: C(C(=O)O)C(CC(=O)O)(C(=O)O)O
Isomeric SMILES: C(C(=O)O)C(CC(=O)O)(C(=O)O)O
InChI: InChI=1S/C6H8O7/c7-3(8)1-6(13,5(11)12)2-4(9)10/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12)
InChIKey: KRKNYBCHXYNGOX-UHFFFAOYSA-N
Molfile

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

Physical properties

TemperaturePressureDensity

Appearance: Citric acid appears as colorless, odorless crystals with an acid taste. Denser than water. (USCG, 1999)[1]
3 values
From CAMEO Chemicals, the most authoritative source here.
Value As written Source
–shown Citric acid appears as colorless, odorless crystals with an acid taste. Denser than 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.
– Other Solid; Dry Powder; CBI; Large Crystals; Dry Powder; Large Crystals; Liquid; Other Solid; Dry Powder; Liquid; Liquid; Large Crystals; Liquid [2] EPA Chemical Data Reporting (CDR)
– COLOURLESS CRYSTALS. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
Odor: Odorless[4]
Melting point: 153 °C[3]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source
153 °C 307 °F (anhydrous) (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.
153 °Cshown 153 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
Boiling point: Reported, but no value passed the checks.
The value and why
Decomposes (NTP, 1992) (could not be read; source [1])
Density: 1.54 at 20 °C (68 °F) (USCG, 1999) - Denser than water[1]
Solubility in water: Solubility in water, g/100ml at 20 °C: 59[3]
3 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– greater than or equal to 100 mg/mL at 72 °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.
– In water, 3.83X10+5 mg/L at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Yalkowsky, S.H., He, Yan, Jain, P. Handbook of Aqueous Solubility Data Second Edition. CRC Press, Boca Raton, FL 2010, p. 275
–shown Solubility in water, g/100ml at 20 °C: 59 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
log P: log Kow = -1.64[4]
2 values
Sources disagree; from Hazardous Substances Data Bank (HSDB), the most authoritative.
Value As written Source
–shown log Kow = -1.64 [4] Hazardous Substances Data Bank (HSDB)cites Avdeef A; Seminar on Ionization and Lipophilicity. Log P values measured by pION Inc., Brookline, MA (A. Avdeef and C. Berger) (1997)
– -1.7 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
pKa: pKa = 2.79[4]
Flash point: 100 °C[3]
Autoignition temperature: 1010 °C (1850 °F, POWDER)[4]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source
1010 °C 1850 °F (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.
1010 °Cshown 1850 °F (POWDER) [4] Hazardous Substances Data Bank (HSDB)cites U.S. Coast Guard, Department of Transportation. CHRIS - Hazardous Chemical Data. Volume II. Washington, D.C.: U.S. Government Printing Office, 1984-5.

Value	As written	Source
–shown	Citric acid appears as colorless, odorless crystals with an acid taste. Denser than 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.
–	Other Solid; Dry Powder; CBI; Large Crystals; Dry Powder; Large Crystals; Liquid; Other Solid; Dry Powder; Liquid; Liquid; Large Crystals; Liquid	[2] EPA Chemical Data Reporting (CDR)
–	COLOURLESS CRYSTALS.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
153 °C	307 °F (anhydrous) (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.
153 °Cshown	153 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–	greater than or equal to 100 mg/mL at 72 °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.
–	In water, 3.83X10+5 mg/L at 25 °C	[4] Hazardous Substances Data Bank (HSDB)cites Yalkowsky, S.H., He, Yan, Jain, P. Handbook of Aqueous Solubility Data Second Edition. CRC Press, Boca Raton, FL 2010, p. 275
–shown	Solubility in water, g/100ml at 20 °C: 59	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–shown	log Kow = -1.64	[4] Hazardous Substances Data Bank (HSDB)cites Avdeef A; Seminar on Ionization and Lipophilicity. Log P values measured by pION Inc., Brookline, MA (A. Avdeef and C. Berger) (1997)
–	-1.7	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
1010 °C	1850 °F (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.
1010 °Cshown	1850 °F (POWDER)	[4] Hazardous Substances Data Bank (HSDB)cites U.S. Coast Guard, Department of Transportation. CHRIS - Hazardous Chemical Data. Volume II. Washington, D.C.: U.S. Government Printing Office, 1984-5.

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: 13
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0.5
H-bond donors: 4
H-bond acceptors: 4 computed here · PubChem 7
Rotatable bonds: 5
TPSA (Å²): 132.1 computed here · PubChem 132
Formal charge: 0
XLogP3: -1.7 PubChem
Complexity: 227 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C1 of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C37.51%
H4.20%
O58.29%

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: -1.25 Crippen (Wildman and Crippen 1999)
log S (water solubility): 0.09 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 2.45 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 192.12
log P ≤ 5 (Crippen): -1.25
H-bond donors ≤ 5: 4
H-bond acceptors ≤ 10: 4

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 [5].

Harmful or irritant

H319Causes serious eye irritation
H335May cause respiratory irritation

Precautionary statements: P261, P264+P265, P271, P280, P304+P340, P305+P351+P338, P319, P337+P317, P403+P233, P405, P501

View all classifications (4)

[5] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · WarningH319, H335
[6] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 8.2% (359 of 4373) of reports.
[6] European Chemicals Agency (ECHA) · 4,373 reports · WarningH319, H335
[6] European Chemicals Agency (ECHA) · 2 reports · WarningH319

Exposure limits

MAK (Maximale Arbeitsplatz Konzentration): (inhalable fraction): 2 mg/m[3]

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. If symptoms (such as redness or irritation) develop, immediately transport the victim to a hospital. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]
Fresh air, rest. Refer for medical attention.[3]
Rinse skin with plenty of water or shower. Refer for medical attention .[3]
First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then refer for medical attention.[3]

Storage

Separated from strong oxidants, strong bases, metal nitrates and metals. Dry.[3]
Crystalline citric acid, anhydrous, can be stored in dry form without difficulty, although conditions of high humidity and elevated temperatures should be avoided to prevent caking. Storage should be in tight containers to prevent exposure to moist air. Several granulations are commercially available with the larger particle sizes having less tendency toward caking.[4]
Temperature: Ambient; Venting: Open.[4]
Containers: 230 lb Barrels, bags, kegs, boxes, cartons, fiber drums, bottles.[4]

Incompatibilities

Potentially explosive reaction with metal nitrates.[4]
Reacts with oxidants and bases. Attacks metals.[4]

Safety data sheets on the supplier’s page: Alfa Chemistry, Aladdin Scientific, CD Formulation.

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]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[5]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
[6]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[7]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
[8]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
[9]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[10]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
[11]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[12]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.

Similar structures

Citramalic acid 52%

Tanimoto similarity on Morgan fingerprints (radius 2) with RDKit 2026.09, at least 45%.

Isomers in the library

Isocitric acid