Phthalic acid
Athanor · official
C8H6O4 · 166.13 g/mol
Also called benzene-1,2-dicarboxylic acid
DangerNames and identifiers
- IUPAC name
- phthalic acid
- Synonyms
- benzene-1,2-dicarboxylic acid, 1,2-benzenedicarboxylic acid, o-phthalic acid
+ 34 more
o-dicarboxybenzene, o-benzenedicarboxylic acid, Acide phtalique, Kyselina ftalova, ortho-phthalic acid, DTXSID8021484, 6O7F7IX66E, NSC-5348, DTXCID901484, CHEBI:29069, hydron;phthalate, RefChem:6136, 201-873-2, Pathalic acid, Orthophthalic acid, MFCD00002467, NSC 5348, Sunftal 20, PhthalicAcid-13C2, Copper(ii)phthalate, Fluorescein EP Impurity B, LEADPHTHALATE,DIBASIC, CHEMBL1045, Phthalic-13C Acid, PHTHALICACID, Phthalic Acid-13C2, Acide phtalique [French], Kyselina ftalova [Czech], M 2, CCRIS 1446, HSDB 1339, EINECS 201-873-2, Phthalate standard for IC, BRN 0608199
- Molecular formula
- C8H6O4
- Empirical formula
- C4H3O2
- Molecular weight
- 166.13 g/mol
- Exact mass
- 166.02661
- CAS number
- 88-99-3
- PubChem CID
- 1017
- Canonical SMILES
- C1=CC=C(C(=C1)C(=O)O)C(=O)O
- Isomeric SMILES
- C1=CC=C(C(=C1)C(=O)O)C(=O)O
- InChI
- InChI=1S/C8H6O4/c9-7(10)5-3-1-2-4-6(5)8(11)12/h1-4H,(H,9,10)(H,11,12)
- InChIKey
- XNGIFLGASWRNHJ-UHFFFAOYSA-N
- Molfile
Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.
Physical properties
TemperaturePressureDensity
- Appearance
- Plates from water[4]
5 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source – Phthalic acid appears as white crystals or fine white powder. (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. – CRYSTALLINE POWDER. [2] ILO-WHO International Chemical Safety Cards (ICSCs) – White crystals or a fine white powder. [3] Occupational Safety and Health Administration (OSHA) – Colorless crystals [4] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 14th Edition. John Wiley & Sons, Inc. New York, NY 2001., p. 875 –shown Plates from water [4] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V1: 797 - Melting point
- 210 to 211 °C (410 to 412 °F) (decomposes) (NTP, 1992)[1]
3 values
2 of 3 sources agree on it (most common value).
Value As written Source 210 to 211 °Cshown 410 to 412 °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. 191.0 °C Melting point = 464.15 K (determined in a sealed tube) [4] Hazardous Substances Data Bank (HSDB)cites Daubert, T.E., R.P. Danner. Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis, 1989. 210 to 211 °C 410-412 °F [3] Occupational Safety and Health Administration (OSHA) 2 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
- Boiling point
- Boiling point = 598.00 K (Based on predicted value for phthalic acid by Meissner's method with a suitable adjustment for isomerism based on similar compound relationships.)[4]
- Density
- 1.593 g/cu cm at 15 °C[4]
5 values
Only one source reports it.
Value As written Source – 1.593 at 68 °F (NTP, 1992) - Denser than water [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. 1.593 g/mLshown 1.593 g/cu cm at 15 °C [4] Hazardous Substances Data Bank (HSDB)cites Gerhartz, W. (exec ed.). Ullmann's Encyclopedia of Industrial Chemistry. 5th ed.Vol A1: Deerfield Beach, FL: VCH Publishers, 1985 to Present., p. VA20: 182 (1992) – Relative density (water = 1): 1.6 [2] ILO-WHO International Chemical Safety Cards (ICSCs) – 1.593 [3] Occupational Safety and Health Administration (OSHA) – 2.18 @ 191°C [5] PAC Chemical Database, U.S. Department of Energy 1 more value was reported but failed the checks (unreadable or out of range), so it is not shown.
- Solubility in water
- Solubility in water, g/100ml at 25 °C: 0.625 (poor)[2]
4 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source – less than 1 mg/mL 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. – Soluble in alcohol; sparingly soluble in ether [4] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 14th Edition. John Wiley & Sons, Inc. New York, NY 2001., p. 875 – In water, 6,965 mg/L at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Yalkowsky, S.H., He, Yan., Handbook of Aqueous Solubility Data: An Extensive Compilation of Aqueous Solubility Data for Organic Compounds Extracted from the AQUASOL dATAbASE. CRC Press LLC, Boca Raton, FL. 2003., p. 456 –shown Solubility in water, g/100ml at 25 °C: 0.625 (poor) [2] ILO-WHO International Chemical Safety Cards (ICSCs) - log P
- 0.73[2]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source – log Kow = 0.73 [4] Hazardous Substances Data Bank (HSDB)cites Hansch, C., Leo, A., D. Hoekman. Exploring QSAR - Hydrophobic, Electronic, and Steric Constants. Washington, DC: American Chemical Society., 1995., p. 38 –shown 0.73 [2] ILO-WHO International Chemical Safety Cards (ICSCs) - pKa
- pKa1 = 2.76[4]
2 values
Only one source reports it.
Value As written Source –shown pKa1 = 2.76 [4] Hazardous Substances Data Bank (HSDB)cites Serjeant EP, Dempsey B; IUPAC Chemical Data Series No 23 NY, NY: Pergamon Press (1979) – pKa2 = 4.92 at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Serjeant EP, Dempsey B; IUPAC Chemical Data Series No 23 NY, NY: Pergamon Press (1979) - Vapor pressure
- 6.36 × 10⁻⁷ mmHg at 25 °C[4]
- Flash point
- 168 °C c.c.[2]
4 values
4 of 4 sources agree on it (most common value).
Value As written Source 168 °C 334 °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. 168 °C 334 °F (168 °C) (Closed cup) [4] Hazardous Substances Data Bank (HSDB)cites Fire Protection Guide to Hazardous Materials. 13 ed. Quincy, MA: National Fire Protection Association, 2002., p. 325-99 168 °Cshown 168 °C c.c. [2] ILO-WHO International Chemical Safety Cards (ICSCs) 168 °C 334 °F [3] Occupational Safety and Health Administration (OSHA)
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
- 12
- Rings
- 1
- Aromatic rings
- 1
- Fraction sp³ carbons (Fsp3)
- 0
- H-bond donors
- 2
- H-bond acceptors
- 2 computed here · PubChem 4
- Rotatable bonds
- 2
- TPSA (Ų)
- 74.6
- Formal charge
- 0
- XLogP3
- 0.7 PubChem
- Complexity
- 177 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
- C57.84%
- H3.64%
- O38.52%
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
- 1.08 Crippen (Wildman and Crippen 1999)
- log S (water solubility)
- -1.79 ESOL (Delaney 2004), log mol/L
- Synthetic accessibility
- 1.4 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)
Drug-likeness: Lipinski’s rule of five
- Molecular weight ≤ 500: 166.13
- log P ≤ 5 (Crippen): 1.08
- 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
Danger
Harmonized EU classification (CLP Annex VI). Source [6].
- Health hazard
Precautionary statements: P203, P280, P318, P405, P501
View all classifications (3)
- [6] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerNo hazard statements
- [7] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 1.1% (3 of 284) of reports.
- [7] European Chemicals Agency (ECHA) · 284 reports · DangerH315, H318, H319, H335
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]
- Fresh air, rest.[2]
- Rinse and then wash skin with water and soap.[2]
- Rinse with plenty of water for several minutes (remove contact lenses if easily possible).[2]
Incompatibilities
- Mixtures of sodium nitrite and phthalic acid or phthalic anhydride explode violently on heating. A nitrite ester may have been produced.[4]
- The exothermic nitration of phthalic acid or phthalic anhydride by a fuming nitric acid-sulfuric acid mixture may give mixtures of the potentially explosive phthaloyl nitrates or nitrites or their nitro derivatives. Formation of these cmpd may be avoided if nitrating mixture is extensively diluted with sulfuric acid and if a small (1.5 mole equiv) (amount) of nitric acid is present.[4]
Safety data sheets on the supplier’s page: J&H Chemical Co.,ltd, Enamine, abcr GmbH.
Always read the supplier’s safety data sheet before working with it.
Spectra
- NMRHazardous Substances Data Bank (HSDB) · NMRShiftDB
- 1H NMRHuman Metabolome Database (HMDB) (Bruker · 600 MHz · Water) · SpectraBase
- 13C NMRSpectraBase
- 1H-13C NMRHuman Metabolome Database (HMDB) (Bruker · 600 MHz · Water)
- GC-MSHuman Metabolome Database (HMDB) (EI-B · positive) · Human Metabolome Database (HMDB) (EI-B · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF (Pegasus III TOF-MS system, Leco; GC 6890, Agilent Technologies) · Positive) · MassBank Europe (Pegasus III TOF-MS system, Leco; GC 6890, Agilent Technologies · GC-EI-TOF · POSITIVE)
- MS-MSHuman Metabolome Database (HMDB) (Quattro_QQQ · Positive) · Human Metabolome Database (HMDB) (Quattro_QQQ · Positive) · Human Metabolome Database (HMDB) (Quattro_QQQ · Positive) · Human Metabolome Database (HMDB) (Negative) · Human Metabolome Database (HMDB) (Negative) · Human Metabolome Database (HMDB) (Negative)
- LC-MSMassBank Europe (TripleTOF 6600 SCIEX · LC-ESI-QTOF · NEGATIVE) · MassBank Europe (API3000, Applied Biosystems · LC-ESI-QQ · NEGATIVE) · MassBank Europe (API3000, Applied Biosystems · LC-ESI-QQ · NEGATIVE) · MassBank Europe (API3000, Applied Biosystems · LC-ESI-QQ · NEGATIVE) · MassBank Europe (API3000, Applied Biosystems · LC-ESI-QQ · NEGATIVE) · MassBank Europe (API3000, Applied Biosystems · LC-ESI-QQ · NEGATIVE)
- Other MSHazardous Substances Data Bank (HSDB) · MassBank Europe (HITACHI M-80A · EI-B · POSITIVE) · MassBank Europe (GCMS-2010 Plus, Shimadzu · EI-B · POSITIVE) · MassBank of North America (MoNA) (Agilent 6550 iFunnel · Q-TOF · ESI) · MassBank of North America (MoNA) (Agilent 6550 iFunnel · Q-TOF · ESI) · MassBank of North America (MoNA) (Agilent 6550 iFunnel · Q-TOF · ESI)
- UVHazardous Substances Data Bank (HSDB)
- IRHazardous Substances Data Bank (HSDB)
- FTIRSpectraBase (Bruker IFS 85 · KBr-Pellet)
- ATR-IRSpectraBase
- Vapor Phase IRSpectraBase (DIGILAB FTS-14 · Vapor Phase)
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]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
- [3]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
- [4]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
- [5]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
- [6]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
- [7]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
- [8]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
- [9]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
- [10]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
- [11]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
- [12]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
- [13]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.