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CAS 121-91-5

CAS 121-91-5 matches 0 EU annex records across Annex II–VI of Regulation 1223/2009.

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Chemical identity and properties

PubChem 2D chemical structure for CAS 121-91-5
CAS 121-91-5PubChem CID 8496

Isophthalic Acid

Isophthalic acid is a benzenedicarboxylic acid that is benzene substituted by carboxy groups at position 1 and 3. One of three possible isomers of benzenedicarboxylic acid, the others being phthalic and terephthalic acids. It is a conjugate acid of an isophthalate(1-). — ChEBI

IUPAC name
benzene-1,3-dicarboxylic acid
Molecular formula
C8H6O4
Molecular weight
166.13 g/mol
Exact mass
166.02660867 Da
XLogP3
1.7
Topological polar surface area
74.6 Ų
Hydrogen-bond donors
2
Hydrogen-bond acceptors
4
Covalent units
1
Defined stereocentres
0

Also known as

1,3-Benzenedicarboxylic acidm-Phthalic acidm-Benzenedicarboxylic acidAcide isophtaliqueKyselina isoftalovaNSC-15310CHEBI:30802benzene-1,3-dicarboxylate;hydron
16 more reported names
RefChem:7642204-506-4Isophthalatem-DicarboxybenzeneNSC 15310Acide isophtalique [French]Kyselina isoftalova [Czech]meta-benzenedicarboxylic acidHSDB 2090EINECS 204-506-4BRN 1909332AI3-16107WLN: QVR CVQ4-09-00-03292 (Beilstein Handbook Reference)iso-phthalic acid3-Carboxybenzoic acid; Isoterephthalic acid; NSC 15310; m-Benzenedicarboxylic acid
Open full PubChem recordPubChem annotations3D structure image
External database identifiers

Evidence from additional scientific databases

NIH PubChem PUG-View
Exact identifier match8496

Attributed physical-property, hazard, environmental and use annotations.

  • First Aid: INHALATION: remove victim to uncontaminated area; get medical attention if complications arise.; INGESTION: get medical attention if complications arise.; EYES: flush with large amounts of water for 15 min.; get prompt medical attention.; SKIN: wash with water. (USCG, 1999) Source: CAMEO Chemicals
  • Note: This chemical does not meet GHS hazard criteria for 91% (614 of 675) of all reports. Source: European Chemicals Agency (ECHA)
  • GHS Hazard Statements: Not Classified; Reported as not meeting GHS hazard criteria by 614 of 675 companies (only 9% companies provided GHS information). For more detailed information, please visit ECHA C&L website. Source: European Chemicals Agency (ECHA)
  • ECHA C&L Notifications Summary: Aggregated GHS information provided per 675 reports by companies from 9 notifications to the ECHA C&L Inventory.; Reported as not meeting GHS hazard criteria per 614 of 675 reports by companies.; There are 5 notifications provided by 61 of 675 reports by companies with hazard statement code(s).; Information may vary between notifications depending on impurities, additives, and other factors. The percentage value in parenthesis indicates the notified classification ratio from companies that provide hazard codes. Only hazard codes with percentage values above 10% are shown. For more detailed information, please visit ECHA C&L website. Source: European Chemicals Agency (ECHA)
  • Environmental Bioconcentration: An estimated BCF of 3 was calculated in fish for isophthalic acid(SRC), using a log Kow of 1.66(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low. Source: Hazardous Substances Data Bank (HSDB)
  • Environmental Fate: TERRESTRIAL FATE: Based on a recommended classification scheme(1), an estimated Koc value of 79(SRC), derived from a molecular structure estimation method(2), suggests that isophthalic acid will have high mobility in soil(SRC). It is a dibasic (2 displaceable hydrogen atoms) acid whose pKa1 is 3.70 and pKa2 is 4.60 at 25 °C(3) and will primarily exist in the anion form in the environment and form salts with cations in soil; anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4). Volatilization of isophthalic acid from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 2.2X10-12 atm-cu m/mole(SRC), using a fragment constant estimation method(5). It absorbs UV radiation >290 nm(6), and therefore may degrade by direct photolysis on the soil surface(SRC). Isophthalic acid is readily biodegradable in screening tests using sewage sludge(7-10) and may be expected to biodegrade in soil(8). Source: Hazardous Substances Data Bank (HSDB)
  • Environmental Fate: AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 79(SRC), determined from a structure estimation method(2), indicates that isophthalic acid is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon an estimated Henry's Law constant of 2.2X10-12 atm-cu m/mole(SRC), developed using a fragment constant estimation method(4). Isophthalic acid is a dibasic (2 displaceable hydrogen atoms) acid whose pKa1 is 3.70 and pKa2 is 4.60 at 25 °C(5) and will be largely dissociated in at an environmental pH range of pH 5 to pH 9(SRC). According to a classification scheme(6), an estimated BCF of 3(SRC), from an estimated log Kow of 1.66(7) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is low. Isophthalic acid absorbs UV radiation >290 nm(9), and therefore may be susceptible to direct photolysis in surface waters(SRC). Isophthalic acid is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(3). Isophthalic acid has been shown to be readily biodegradable in screeni Source: Hazardous Substances Data Bank (HSDB)
  • Environmental Fate: ATMOSPHERIC FATE: According to a theory of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), isophthalic acid, which has an estimated vapor pressure of 2.6X10-8 mm Hg at 25 °C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Its existence in the atmosphere in both phases has been observed experimentally(3,4). Vapor-phase isophthalic acid is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 12 days(SRC), calculated from its rate constant of 1.3X10-12 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(5). Particulate-phase isophthalic acid may be physically removed from the air by wet and dry deposition(SRC). Isophthalic acid absorbs at wavelengths >290 nm(6), and therefore may be susceptible to direct photolysis by sunlight(SRC). Source: Hazardous Substances Data Bank (HSDB)
  • Sources/Uses: Used to make plastics, unsaturated polyester resins, alkyd resins, polyamides, and thermoplastic polyesters; Used as a co-monomer with terephthalic acid to make plastic bottles and specialty resins; [HSDB] Used in formulations for adhesives, inks, wire enamels, and dental materials; [CAMEO] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
  • Industrial Processes with risk of exposure: Working with Glues and Adhesives [Category: Other]; Plastic Composites Manufacturing [Category: Industry] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
  • Uses: CHEM INT FOR DIPHENYL ISOPHTHALATE Source: Hazardous Substances Data Bank (HSDB)
  • Uses: CHEM INT FOR THE PLASTICIZER, DIOCTYL ISOPHTHALATE, DIMETHYL ISOPHTHALATE & DIETHYL ISOPHTHALATE Source: Hazardous Substances Data Bank (HSDB)
  • Uses: CHEM INT FOR DIALLYL ISOPHTHALATE (CROSS LINKING AGENT) Source: Hazardous Substances Data Bank (HSDB)
  • Uses: Isophthalic acid is used as a raw material in the production of polyesters. About 35% of the isophthalic acid is used to prepare unsaturated polyester resins, about 30% is used to produce alkyd coatings, and over 20% is used in other types of polymers, primarily as a minor comonomer with terephthalic acid in saturated polyesters. Isophthalic acid is also used in formulations for adhesives, inks, wire enamels, and dental materials. In addition, it is used to produce derivative chemicals such as the diesters. Source: Hazardous Substances Data Bank (HSDB)
  • Uses: Isophthalic acid is used as a comonomer with terephthalic acid in bottle and specialty resins. It is also a feedstock for coatings and for high-performance unsaturated polyesters, being first reacted with maleic anhydride and then this resin is cross-linked with styrene. Source: Hazardous Substances Data Bank (HSDB)

Mapped by: Existing checksum-valid CAS to unique PubChem CID match. Retrieved: 2026-08-31. Open source record

Scientific classifications and hazard annotations provide context and do not replace the market-specific regulatory decision shown above.

Additional source coverage and match status
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NIH PubChem PUG-ViewExact match2026-08-31

A recorded no-match is useful evidence that the source was checked; it is not a claim that the substance does not exist elsewhere.

Retrieved from NIH PubChem on 2026-08-31 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

Records for CAS 121-91-5

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How CAS 121-91-5 is used on this site

CAS 121-91-5 is the Chemical Abstracts Service identifier used to pin this page to a specific substance. In the current dataset, 0 EU annex records share this identifier, which helps you cross-check whether the same substance appears under one regulatory context or several.

Use this page when a supplier specification, SDS or raw-material dossier gives you CAS 121-91-5 and you need to see every linked Annex II–VI record in one place. The entry cards above are the quickest route to concentration limits, warnings, annex placement and product-type conditions.