Organic and polymer intermediate
Sigma documents preparation of intermediates including 4-acetoxybenzoic acid; attributed industrial references identify polyester/liquid-crystal-polymer synthesis. [5]
01
THE ESSENTIALS
4-Hydroxybenzoic Acid in 30 Seconds
OH and COOH occupy opposite ring positions, 1 and 4. The phenolic hydroxyl does not make this a dicarboxylic acid, and the molecule has no stereocenter.
4-Hydroxybenzoic acid is the para phenolic acid. Its esters include parabens, which are different chemical products with their own uses and regulatory requirements. [1] [3]
Safety at a glance — Sigma H20059 identifies serious eye damage and respiratory irritation; TCI identifies eye irritation and aquatic harm. Retain the serious-eye-damage warning and avoid environmental release. Paraben ingredient contexts do not make the free-acid powder suitable for direct skin or food use. [4] [5] [6]
A condensed structural formula keeps the functional groups visible. [1]
02
GO A LITTLE DEEPER
Understanding 4-Hydroxybenzoic Acid
THE SIMPLE EXPLANATION
The functional groups
OH and COOH occupy opposite ring positions, 1 and 4. The phenolic hydroxyl does not make this a dicarboxylic acid, and the molecule has no stereocenter. [1]
A LITTLE DEEPER
What the structure changes
The phenolic OH and COOH can participate in different reactions and dissociations. Esterifying the carboxyl group produces a paraben derivative; preservative claims for that ester are not automatically direct uses of the free acid. [1] [12]
Technical detail Identity, dissociation & specification
Connectivity and neutral formula identify this acid. Positional isomers, water-containing products, salts and esters require their own specifications. Measured reference conditions, assay methods and unresolved discrepancies remain visible. [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 4-Hydroxybenzoic Acid Compares
Similar names and functional groups do not mean interchangeable chemicals.
SIDE-BY-SIDE COMPARISON
4-Hydroxybenzoic Acid vs 3-Hydroxybenzoic Acid
Para phenolic monocarboxylic acid
versusMeta phenolic monocarboxylic acid
Fixed comparison for this prototype. Acid selectors are disabled; additional comparisons are coming later.
| Property | 4-Hydroxybenzoic Acid | 3-Hydroxybenzoic Acid |
|---|---|---|
| Molecular formula | C₇H₆O₃ [1] | C₇H₆O₃ [7] |
| Molecular weight | 138.12 g/mol [1] | 138.12 g/mol [7] |
| Carbon atoms | 7 [1] | 7 [7] |
| Carboxyl groups | 1 [1] | 1 [7] |
| Structure | 4-HO–C₆H₄–COOH [1] | 3-HO–C₆H₄–COOH [7] |
| Chemical family | Para phenolic monocarboxylic acid [1] | Meta phenolic monocarboxylic acid [7] |
| Identity focus | Neutral free acid; water and derivatives specified separately [1] | Neutral free acid; water and derivatives specified separately [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 4-hydroxybenzoic acid for a specified para synthesis or analytical target; choose the 3-isomer for a meta target. If the intended material is a paraben, identify and qualify that exact ester separately. [1] [3] [7]
Specified starting material
4-Hydroxybenzoic Acid
Match 4-HO–C₆H₄–COOH and the method’s required chemical form.
3-Hydroxybenzoic Acid
Match 3-HO–C₆H₄–COOH; 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 4-Hydroxybenzoic Acid Used For?
Organic and polymer intermediate
Sigma documents preparation of intermediates including 4-acetoxybenzoic acid; attributed industrial references identify polyester/liquid-crystal-polymer synthesis. Final polymer performance is separate from the free acid. [5]
Food-analysis standard context
Wako 089-10561 is explicitly a p-hydroxybenzoic-acid standard for food analysis, with qNMR and HPLC specifications. This is direct analytical use, not qualification as a food additive. [6]
06
SOURCE WITH CONTEXT
4-Hydroxybenzoic Acid Suppliers
Compare specific products and package options. Listings are not ranked recommendations.
3 suppliers · 3 products · 7 package listingsLatest supplier check: October 3, 2026
Package sizes stay grouped under the supplier product. Assay methods, product forms, and regional markets remain visible. The Wako 100 mg qNMR/HPLC standard is not equivalent to TCI or Sigma bulk reagents. Food analysis is not food-ingredient grade. Keep positional identity, assay method and ester identity distinct.
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 America4-Hydroxybenzoic Acid | Named grade not statedH0207 · 25 g | GC: minimum 99.0% Neutralization titration: minimum 99.0% | 25 g | $18.00USD · US public price | Not comparedGrades, assay bases, or forms differ | Document notes: TCI America
| View Product: TCI America, H0207 · 25 g (opens new tab) | |
| Named grade not statedH0207 · 100 g | GC: minimum 99.0% Neutralization titration: minimum 99.0% | 100 g | $24.00USD · US public price | Not comparedGrades, assay bases, or forms differ | View Product: TCI America, H0207 · 100 g (opens new tab) | |||
| Named grade not statedH0207 · 500 g | GC: minimum 99.0% Neutralization titration: minimum 99.0% | 500 g | $49.00USD · US public price | Not comparedGrades, assay bases, or forms differ | View Product: TCI America, H0207 · 500 g (opens new tab) | |||
| Sigma-Aldrich4-Hydroxybenzoic Acid | ReagentPlusH20059-100G | 99%; method not stated | 100 g | $36.30USD · US public list price | Not comparedGrades, assay bases, or forms differ | Document notes: Sigma-Aldrich
| View Product: Sigma-Aldrich, H20059-100G (opens new tab) | |
| ReagentPlusH20059-500G | 99%; method not stated | 500 g | $113.00USD · US public list price | Not comparedGrades, assay bases, or forms differ | View Product: Sigma-Aldrich, H20059-500G (opens new tab) | |||
| ReagentPlusH20059-1KG | 99%; method not stated | 1 kg | $114.00USD · US public list price | Not comparedGrades, assay bases, or forms differ | View Product: Sigma-Aldrich, H20059-1KG (opens new tab) | |||
| FUJIFILM Wako4-Hydroxybenzoic Acid | Standard for food analysis089-10561Research / further manufacturing; confirm US availability separately from Japan stock. Food-analysis standard is not food-ingredient grade. Out-of-stock status was displayed; 2–10 °C storage and argon packaging apply to this product. | 98.0+% (qNMR); 98.0+% (HPLC) | 100 mg | $141.00USD · US catalog list price | Not comparedGrades, assay bases, or forms differ | Document notes: FUJIFILM Wako
| View Product: FUJIFILM Wako, 089-10561 (opens new tab) |
TCI America
4-Hydroxybenzoic Acid
Neutralization titration: minimum 99.0%
Named grade not stated
25 g
H0207 · 25 g- Public price
- $18.00USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
100 g
H0207 · 100 g- Public price
- $24.00USD · US public price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
500 g
H0207 · 500 g- Public price
- $49.00USD · 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
4-Hydroxybenzoic Acid
ReagentPlus
100 g
H20059-100G- Public price
- $36.30USD · US public list price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
500 g
H20059-500G- Public price
- $113.00USD · US public list price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
1 kg
H20059-1KG- Public price
- $114.00USD · US public list price
- Normalized price
- Not comparedGrades, assay bases, or forms differ
Documentation
Document notes: Sigma-Aldrich
- 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
4-Hydroxybenzoic Acid
Standard for food analysis
Research / further manufacturing; confirm US availability separately from Japan stock. Food-analysis standard is not food-ingredient grade. Out-of-stock status was displayed; 2–10 °C storage and argon packaging apply to this product.
100 mg
089-10561- Public price
- $141.00USD · 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
pKa: OMITTED. An attributed 4.54 lacks matched conditions; separate K1/K2 values at 19 °C have incomplete method context. No borrowed salicylic value or condition-free pair. Solubility: CONDITION-DEPENDENT. 5.0 g/L at 25 °C is an attributed reference; temperature-free parts-water wording is not converted into a competing saturation constant. Boiling point: OMITTED. A generic scent-database estimate is not an authoritative measured normal boiling point.
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 4-Hydroxybenzoic 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 4-Hydroxybenzoic Acid
Selections remain only while this page is open.
09
FOR YOUR REFERENCE
4-Hydroxybenzoic Acid Technical Reference
Identity, product reference properties, and handling context.
Identification Names, formula & identifiers
- Principal CAS
- 99-96-7
- Identity focus
- Neutral free acid; water and derivatives specified separately
- Formula
- C₇H₆O₃
- Molecular weight
- 138.12 g/mol
- IUPAC name
- 4-hydroxybenzoic acid
- Connectivity SMILES
- C1=CC(=CC=C1C(=O)O)O
- Identity SMILES
- C1=CC(=CC=C1C(=O)O)O
- InChI
- InChI=1S/C7H6O3/c8-6-3-1-5(2-4-6)7(9)10/h1-4,8H,(H,9,10)
- PubChem CID
- 135
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; melting references and specifications are for the para free acid. [13] [4] [5]
- Melting specification
- TCI H0207: 214–219 °C; Sigma literature reference 213–217 °C [4]
- Water-solubility reference
- Attributed Yalkowsky: 5.0 g/L at 25 °C; measurement method not stated in retrieved entry [13]
- Solid density reference
- Attributed CRC: 1.46 g/cm³ at 25 °C; not bulk powder density [13]
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]
pKa: OMITTED. An attributed 4.54 lacks matched conditions; separate K1/K2 values at 19 °C have incomplete method context. No borrowed salicylic value or condition-free pair. Solubility: CONDITION-DEPENDENT. 5.0 g/L at 25 °C is an attributed reference; temperature-free parts-water wording is not converted into a competing saturation constant. Boiling point: OMITTED. A generic scent-database estimate is not an authoritative measured normal boiling point.
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
Sigma H20059 identifies serious eye damage and respiratory irritation; TCI identifies eye irritation and aquatic harm. Retain the serious-eye-damage warning and avoid environmental release. Paraben ingredient contexts do not make the free-acid powder suitable for direct skin or food use. [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
4-Hydroxybenzoic Acid FAQ
What distinguishes 4-Hydroxybenzoic Acid?
OH and COOH occupy opposite ring positions, 1 and 4. The phenolic hydroxyl does not make this a dicarboxylic acid, and the molecule has no stereocenter. [1]
How does it differ from 3-Hydroxybenzoic Acid?
The para and meta acids share a formula while supplying different attachment geometry. A para hydroxy-acid residue in a polymer or derivative cannot be substituted with meta acid merely because molecular weights match. [7]
What must a buyer specify?
The Wako 100 mg qNMR/HPLC standard is not equivalent to TCI or Sigma bulk reagents. Food analysis is not food-ingredient grade. Keep positional identity, assay method and ester identity distinct. [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?
pKa: OMITTED. An attributed 4.54 lacks matched conditions; separate K1/K2 values at 19 °C have incomplete method context. No borrowed salicylic value or condition-free pair. Solubility: CONDITION-DEPENDENT. 5.0 g/L at 25 °C is an attributed reference; temperature-free parts-water wording is not converted into a competing saturation constant. Boiling point: OMITTED. A generic scent-database estimate is not an authoritative measured normal boiling point.
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 · 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.
- 3-Hydroxybenzoic Acid · identity (opens new tab)
Primary structural comparison. Practical interpretation does not establish suitability.
- Salicylic Acid · identity (opens new tab)
Related identity and structural relationship.
- Benzoic Acid · identity (opens new tab)
Related identity and structural relationship.
- Gallic Acid · identity (opens new tab)
Related identity and structural relationship.
- 3-Hydroxybenzoic 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 and conditions reviewed; unsupported estimates and cross-isomer data excluded.
Review limits
pKa: OMITTED. An attributed 4.54 lacks matched conditions; separate K1/K2 values at 19 °C have incomplete method context. No borrowed salicylic value or condition-free pair. Solubility: CONDITION-DEPENDENT. 5.0 g/L at 25 °C is an attributed reference; temperature-free parts-water wording is not converted into a competing saturation constant. Boiling point: OMITTED. A generic scent-database estimate is not an authoritative measured normal boiling point.
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.