Polyester intermediate
Attributed industrial references identify isophthalic acid as a polyester synthesis component. [3]
01
THE ESSENTIALS
Isophthalic Acid in 30 Seconds
One ring carbon lies between the two COOH-bearing carbons along the shorter ring path. This positional arrangement differs from both neighboring ortho groups and opposite para groups; the neutral identity is achiral.
Isophthalic acid is the meta, or 1,3, benzene diacid. It shares a formula with phthalic acid while giving a different connectivity and polymer residue. [1] [3]
Safety at a glance — Control dust and eye/skin contact for the supplied solid and obtain its exact local SDS. Accessible product pages do not supply a consistent hazard classification, and an unclassified supplier extract is not evidence that exposure or heating is harmless. High-temperature phase data include sublimation references; avoid treating them as routine boiling instructions. [4] [5] [6]
A condensed structural formula keeps the functional groups visible. [1]
02
GO A LITTLE DEEPER
Understanding Isophthalic Acid
THE SIMPLE EXPLANATION
The functional groups
One ring carbon lies between the two COOH-bearing carbons along the shorter ring path. This positional arrangement differs from both neighboring ortho groups and opposite para groups; the neutral identity is achiral. [1]
A LITTLE DEEPER
What the structure changes
Its carboxyl groups can form ester linkages or metal-binding carboxylates. The resulting polyester or coordination material has properties of its own. Apparent aqueous solubility also changes when pH converts free acid into more soluble ionic forms. [1] [12]
Technical detail Identity, dissociation & specification
The molecular formula specifies the neutral free acid. A commercial solution, salt, ester or anhydride needs its own composition and specification. Quantitative references retain temperature, pressure, product identity and unresolved method qualifiers. [1] [2] [4] [5] [6]
Acid–base reference values describe equilibria under specified conditions. They are not a substitute for a validated formulation or an assay on the purchased lot.
03
MAKE THE CONNECTION
How Isophthalic Acid Compares
Similar names and functional groups do not mean interchangeable chemicals.
SIDE-BY-SIDE COMPARISON
Isophthalic Acid vs Phthalic Acid
Meta aromatic dicarboxylic acid
versusOrtho aromatic dicarboxylic acid
Fixed comparison for this prototype. Acid selectors are disabled; additional comparisons are coming later.
| Property | Isophthalic Acid | Phthalic Acid |
|---|---|---|
| Molecular formula | C₈H₆O₄ [1] | C₈H₆O₄ [7] |
| Molecular weight | 166.13 g/mol [1] | 166.13 g/mol [7] |
| Carbon atoms | 8 [1] | 8 [7] |
| Carboxyl groups | 2 [1] | 2 [7] |
| Structure | 1,3-C₆H₄(COOH)₂ [1] | 1,2-C₆H₄(COOH)₂ [7] |
| Chemical family | Meta aromatic dicarboxylic acid [1] | Ortho aromatic dicarboxylic acid [7] |
| Identity focus | Free acid [1] | Free acid [7] |
Chemical identities are compared here; supplier grades, concentrations, and stereochemical specifications are separate purchasing attributes. pKa values retain their stated conditions; no quantitative solubility ranking is implied.
When Might You Choose One Instead of the Other?
Choose isophthalic acid when a polyester, coordination-material or analytical method specifies the meta residue. Choose phthalic acid for an ortho target. Validate isomer, water, impurity and process specifications rather than substituting on molecular weight or titration alone. [1] [3] [7]
Specified starting material
Isophthalic Acid
Match 1,3-C₆H₄(COOH)₂ and the method’s required chemical form.
Phthalic Acid
Match 1,2-C₆H₄(COOH)₂; verify the identity before substituting a related acid.
Before choosing: match the reaction or formulation, then verify the exact form, grade, assay basis, and impurities. These contexts do not establish suitability for an industrial or regulated application.
04
FROM STRUCTURE TO APPLICATION
What Is Isophthalic Acid Used For?
Polyester intermediate
Attributed industrial references identify isophthalic acid as a polyester synthesis component. Resulting resin performance belongs to the polymer, not the free acid. [3]
Coordination-material intermediate
Sigma I19209 documents preparation of metal coordination polymers using isophthalic acid. The acid supplies the ligand precursor; finished-material structure and performance require separate characterization. [5]
06
SOURCE WITH CONTEXT
Isophthalic Acid Suppliers
Compare specific products and package options. Listings are not ranked recommendations.
3 suppliers · 3 products · 6 package listingsLatest supplier check: October 3, 2026
Package sizes stay grouped under the supplier product. Assay methods, product forms, and regional markets remain visible. Wako’s 95% capillary-GC 1st Grade is not equivalent to the 99% TCI or Sigma products. Neutralization titration does not itself prove positional identity. A clear solution in NaOH is not the solubility of neutral acid in water.
Scroll horizontally if needed. Supplier and package identity stay visible.
| Supplier | Product / Grade | Purity / Assay | Package Size | Public Price | Normalized Price | Documentation | Last Checked | Action |
|---|---|---|---|---|---|---|---|---|
| TCI AmericaIsophthalic Acid | Named grade not statedI0155 · 25 g | GC: minimum 99.0% Neutralization titration: minimum 99.0% | 25 g | $17.00USD · US public price | Not comparedGrades, assay bases, or forms differ | Document notes: TCI America
| View Product: TCI America, I0155 · 25 g (opens new tab) | |
| Named grade not statedI0155 · 500 g | GC: minimum 99.0% Neutralization titration: minimum 99.0% | 500 g | $26.00USD · US public price | Not comparedGrades, assay bases, or forms differ | View Product: TCI America, I0155 · 500 g (opens new tab) | |||
| Sigma-Aldrich / MerckIsophthalic Acid | Named grade not statedI19209-500G | 99%; method not stated | 500 g | $52.70USD · US public price | Not comparedGrades, assay bases, or forms differ | Document notes: Sigma-Aldrich / Merck
| View Product: Sigma-Aldrich / Merck, I19209-500G (opens new tab) | |
| Named grade not statedI19209-2KG | 99%; method not stated | 2 kg | $111.00USD · US public price | Not comparedGrades, assay bases, or forms differ | View Product: Sigma-Aldrich / Merck, I19209-2KG (opens new tab) | |||
| FUJIFILM WakoIsophthalic Acid | Wako 1st Grade097-01832Research / further manufacturing. Japan stock does not confirm US availability. 95% specification is not equivalent to the 99% products. US SDS search extract was seen but full document retrieval was unsuccessful; not marked retrieved. | 95.0+% (Capillary GC) | 25 g | $26.00USD · US catalog list price | Not comparedGrades, assay bases, or forms differ | Document notes: FUJIFILM Wako
| View Product: FUJIFILM Wako, 097-01832 (opens new tab) | |
| Wako 1st Grade091-01835Research / further manufacturing. Japan stock does not confirm US availability. 95% specification is not equivalent to the 99% products. US SDS search extract was seen but full document retrieval was unsuccessful; not marked retrieved. | 95.0+% (Capillary GC) | 500 g | $42.00USD · US catalog list price | Not comparedGrades, assay bases, or forms differ | View Product: FUJIFILM Wako, 091-01835 (opens new tab) |
TCI America
Isophthalic Acid
Neutralization titration: minimum 99.0%
Named grade not stated
25 g
I0155 · 25 g- Public price
- $17.00USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
500 g
I0155 · 500 g- Public price
- $26.00USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
Documentation
Document notes: TCI America
- A product-specific certificate retrieval option was visible; no lot certificate was reviewed. Open the product page and use its certificate section.
- A current regional SDS was not verified in this pass.
- Origin-document availability was not verified. Country of origin is unverified and is not inferred.
Last checked:
Sigma-Aldrich / Merck
Isophthalic Acid
Named grade not stated
500 g
I19209-500G- Public price
- $52.70USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
2 kg
I19209-2KG- Public price
- $111.00USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
Documentation
Document notes: Sigma-Aldrich / Merck
- A product-specific certificate retrieval option was visible; no lot certificate was reviewed. Open the product page and use its certificate section.
- A current regional SDS was not verified in this pass.
- Origin-document availability was not verified. Country of origin is unverified and is not inferred.
Last checked:
FUJIFILM Wako
Isophthalic Acid
Wako 1st Grade
Research / further manufacturing. Japan stock does not confirm US availability. 95% specification is not equivalent to the 99% products. US SDS search extract was seen but full document retrieval was unsuccessful; not marked retrieved.
25 g
097-01832- Public price
- $26.00USD · US catalog list price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
500 g
091-01835- Public price
- $42.00USD · US catalog list price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
Documentation
Document notes: FUJIFILM Wako
- A product-specific certificate retrieval option was visible; no lot certificate was reviewed. Open the product page and use its certificate section.
- A current regional SDS was not verified in this pass.
- Origin-document availability was not verified. Country of origin is unverified and is not inferred.
Last checked:
Documentation evidence
COA = Certificate of Analysis · SDS = Safety Data Sheet · COO = Certificate of Origin.
Lookup means a retrieval option was visible, not that a lot certificate was reviewed. Check supplier means availability or the applicable document was not verified.
Prices may vary by quantity, account, contract, geography, and availability. These products have different grades, assay bases, or forms; no normalized comparison is shown. Foreign-market prices are reference listings only. No currency conversion, mass-to-volume conversion, or ranking is applied. Confirm equivalent specifications and a current quote before comparison. [4] [5] [6]
Verification limits & placement policy
Thermal behavior: CONFLICT UNRESOLVED. Supplier and attributed references span roughly 341–348 °C; a sealed-tube value near 346 °C is separately identified. Measurement context partly differs, but a universal clean melting value was not established. Water solubility: CONFLICT RESOLVED. Attributed neutral-water value about 120 mg/L at 25 °C is compatible in scale with TCI 130 mg/L at 25 °C. OECD SIDS 5400 mg/L at 14 °C is pH-adjusted for complete dissociation, not intrinsic neutral-acid solubility; temperature alone is not the explanation. pKa / density: OMITTED. Stepwise compilation values lack fully established method/ionic-strength context; density records do not supply a matched solid measurement suitable for the main field. Boiling point: OMITTED. Attributed sublimation and predicted estimates are not measured normal liquid boiling.
Only the displayed identity, specification, packages, public prices and stated documentation evidence were reviewed. Current stock, lead times, shipping eligibility, contract pricing, lot certificates, and regulatory suitability are unverified.
There are no paid placements. Future paid listings will show “Sponsored” in both views; payment will not determine chemistry interpretation or imply a ranking.
07
PLAN A LARGER ORDER
Need Isophthalic Acid in Bulk?
Turn your requirements into a clear supplier brief.
Bulk RFQ feature — coming soon. Prototype form: submissions are not currently sent to suppliers. Use sample details to prepare an on-screen brief.
Prepare a bulk request Prototype form
08
A BUYER’S CHECKLIST
Before You Buy Isophthalic Acid
Selections remain only while this page is open.
09
FOR YOUR REFERENCE
Isophthalic Acid Technical Reference
Identity, product reference properties, and handling context.
Identification Names, formula & identifiers
- Principal CAS
- 121-91-5
- Identity focus
- Free acid
- Formula
- C₈H₆O₄
- Molecular weight
- 166.13 g/mol
- IUPAC name
- benzene-1,3-dicarboxylic acid
- Connectivity SMILES
- C1=CC(=CC(=C1)C(=O)O)C(=O)O
- Identity SMILES
- C1=CC(=CC(=C1)C(=O)O)C(=O)O
- InChI
- InChI=1S/C8H6O4/c9-7(10)5-2-1-3-6(4-5)8(11)12/h1-4H,(H,9,10)(H,11,12)
- PubChem CID
- 8496
Connectivity SMILES describes connectivity; it is not an independent stereochemical assignment. CAS and product-form distinctions are supported by the supplier listings. [1] [4] [5] [6]
Physical Properties Product references & conditions
Solid at 20 °C. High-temperature melting references vary by source and method; a sublimation record is not ordinary liquid boiling. [13] [4] [5]
- Thermal references
- Sigma I19209: 341–343 °C literature reference; TCI: 348 °C reference. Method differences remain incompletely resolved. [5]
- Water-solubility reference
- TCI I0155: 0.13 g/L at 25 °C; measurement method not stated [4]
Hydrate, concentration, stereoisomer, and temperature can change the relevant specification. Product reference data are not a reviewed lot certificate.
Acid/Base Properties Verified values & missing data
A numeric pKa was not verified for the selected identity in this review; no value is inferred. [2]
Thermal behavior: CONFLICT UNRESOLVED. Supplier and attributed references span roughly 341–348 °C; a sealed-tube value near 346 °C is separately identified. Measurement context partly differs, but a universal clean melting value was not established. Water solubility: CONFLICT RESOLVED. Attributed neutral-water value about 120 mg/L at 25 °C is compatible in scale with TCI 130 mg/L at 25 °C. OECD SIDS 5400 mg/L at 14 °C is pH-adjusted for complete dissociation, not intrinsic neutral-acid solubility; temperature alone is not the explanation. pKa / density: OMITTED. Stepwise compilation values lack fully established method/ionic-strength context; density records do not supply a matched solid measurement suitable for the main field. Boiling point: OMITTED. Attributed sublimation and predicted estimates are not measured normal liquid boiling.
Temperature, ionic strength, and the use of activities versus concentrations matter in quantitative work. These reference values are not buffer recipes.
Safety at a Glance Product-specific hazards
Control dust and eye/skin contact for the supplied solid and obtain its exact local SDS. Accessible product pages do not supply a consistent hazard classification, and an unclassified supplier extract is not evidence that exposure or heating is harmless. High-temperature phase data include sublimation references; avoid treating them as routine boiling instructions. [4] [5] [6]
Hazard classifications can vary by concentration, product, supplier and jurisdiction. Review the SDS for the exact product before handling. This summary does not replace the SDS.
Supplier safety information and SDS retrieval (opens new tab)
A product-page safety classification is not verification of every regional SDS. Confirm product code, chemical form and current local document.
Review supplier documentation10
COMMON QUESTIONS
Isophthalic Acid FAQ
What distinguishes Isophthalic Acid?
One ring carbon lies between the two COOH-bearing carbons along the shorter ring path. This positional arrangement differs from both neighboring ortho groups and opposite para groups; the neutral identity is achiral. [1]
How does it differ from Phthalic Acid?
Phthalic acid is 1,2 and isophthalic acid is 1,3. The identical formula cannot distinguish the two. Isophthalic acid does not have the same adjacent-carboxyl arrangement that forms the characteristic phthalic anhydride. [7]
What must a buyer specify?
Wako’s 95% capillary-GC 1st Grade is not equivalent to the 99% TCI or Sigma products. Neutralization titration does not itself prove positional identity. A clear solution in NaOH is not the solubility of neutral acid in water. [4]
Are the listed products directly price-comparable?
No. The table retains differing grades, assay bases, forms, and markets. No normalized ranking or currency conversion is applied. [5]
What reference data still need checking?
Thermal behavior: CONFLICT UNRESOLVED. Supplier and attributed references span roughly 341–348 °C; a sealed-tube value near 346 °C is separately identified. Measurement context partly differs, but a universal clean melting value was not established. Water solubility: CONFLICT RESOLVED. Attributed neutral-water value about 120 mg/L at 25 °C is compatible in scale with TCI 130 mg/L at 25 °C. OECD SIDS 5400 mg/L at 14 °C is pH-adjusted for complete dissociation, not intrinsic neutral-acid solubility; temperature alone is not the explanation. pKa / density: OMITTED. Stepwise compilation values lack fully established method/ionic-strength context; density records do not supply a matched solid measurement suitable for the main field. Boiling point: OMITTED. Attributed sublimation and predicted estimates are not measured normal liquid boiling.
Can I request a bulk quote here?
The RFQ is a prototype that prepares an on-screen brief. Nothing is sent to suppliers. Confirm actual bulk terms directly with the supplier.
11
TRACE THE INFORMATION
Sources & Editorial Notes
Identity and compiled reference values are separated from supplier-specific specifications. Structural comparisons and buyer guidance are editorial interpretation. Sources were checked October 3, 2026; supplier information can change.
- PubChem · chemical identity (opens new tab)
Neutral molecular identity verified independently through PUG REST; CAS also checked on all selected supplier products.
- PubChem / HSDB · dissociation references (opens new tab)
No numeric field promoted: insufficient conditions or unresolved conflicting records.
- PubChem / HSDB · application references (opens new tab)
Attributed application records reviewed claim by claim. Free acid, intermediate, derivative and biological context are distinguished.
- TCI America · commercial product (opens new tab)
Direct product checked October 3, 2026. Identity, listed assay methods, packages, market, prices and documentation interfaces inspected. Lot certificates and stock are not verified.
- Sigma-Aldrich / Merck · commercial product (opens new tab)
Direct product checked October 3, 2026. Identity, listed assay methods, packages, market, prices and documentation interfaces inspected. Lot certificates and stock are not verified.
- FUJIFILM Wako · commercial product (opens new tab)
Direct product checked October 3, 2026. Identity, listed assay methods, packages, market, prices and documentation interfaces inspected. Lot certificates and stock are not verified.
- Phthalic Acid · identity (opens new tab)
Primary structural comparison. Practical interpretation does not establish suitability.
- Benzoic Acid · identity (opens new tab)
Related identity and structural relationship.
- Maleic Acid · identity (opens new tab)
Related identity and structural relationship.
- Fumaric Acid · identity (opens new tab)
Related identity and structural relationship.
- Phthalic Acid · dissociation references (opens new tab)
Only independently reviewed values are promoted into the comparison; no condition-free acidity ranking.
- OpenStax · Carboxylic-acid structure and properties (opens new tab)
General carboxylate resonance, acidity and structural interpretation; not authority for this acid’s quantitative constants.
- PubChem / HSDB · attributed physical references (opens new tab)
Attributed references reviewed; product, phase, pH and method gaps stated rather than inferred.
Review limits
Thermal behavior: CONFLICT UNRESOLVED. Supplier and attributed references span roughly 341–348 °C; a sealed-tube value near 346 °C is separately identified. Measurement context partly differs, but a universal clean melting value was not established. Water solubility: CONFLICT RESOLVED. Attributed neutral-water value about 120 mg/L at 25 °C is compatible in scale with TCI 130 mg/L at 25 °C. OECD SIDS 5400 mg/L at 14 °C is pH-adjusted for complete dissociation, not intrinsic neutral-acid solubility; temperature alone is not the explanation. pKa / density: OMITTED. Stepwise compilation values lack fully established method/ionic-strength context; density records do not supply a matched solid measurement suitable for the main field. Boiling point: OMITTED. Attributed sublimation and predicted estimates are not measured normal liquid boiling.
This informational prototype is not a supplier, quotation service, or endorsement of a product’s fitness for an application. Buyers should verify the applicable specification, certification, and regulatory requirements for their intended use.