Hydroquinone (HQ)

What Is Hydroquinone?

Hydroquinone, commonly abbreviated as HQ, is an aromatic organic compound containing two hydroxyl groups in the para positions of a benzene ring. It is also known as 1,4-benzenediol or quinol.

Hydroquinone is widely used as a polymerization inhibitor, antioxidant, reducing agent and chemical intermediate. Grade selection should be based on the intended monomer system, synthesis process and required impurity controls.

Hydroquinone Identification and Properties

These values are general references. The approved specification and lot-specific Certificate of Analysis take precedence.

How Is Hydroquinone Used as a Polymerization Inhibitor?

Hydroquinone reacts with free radicals and helps delay unwanted polymerization. It is commonly evaluated in acrylic acid, acrylic esters, methacrylic acid, methacrylates, styrene and other polymerizable systems.

In many monomer systems, the effectiveness of Hydroquinone is influenced by the presence of dissolved oxygen. The neat Hydroquinone product itself, however, may require protection from air and light to reduce oxidation during storage.

Inhibitor performance depends on monomer chemistry, oxygen concentration, temperature, contamination and storage time; the inhibitor system must be validated for the specific process.

No inhibitor should be treated as a substitute for proper temperature control, contamination prevention, emergency relief systems or process-safety review.

Where Is Hydroquinone Used?

Acrylic and Methacrylic Monomers

Hydroquinone can help control premature polymerization during the manufacture, processing, storage and transportation of selected acrylic and methacrylic monomers.

Unsaturated Resins and Polymer Systems

It may be used to adjust storage stability or reaction behavior in selected unsaturated polyester, vinyl and resin systems.

Antioxidants and Stabilizers

Hydroquinone is used as an antioxidant, reducing agent or starting material for the production of other stabilizers and polymerization inhibitors.

Dyes and Pigments

It can serve as an organic synthesis intermediate in the manufacture of selected dyes, pigments and color-development chemicals.

Agrochemical and Pharmaceutical Intermediates

Hydroquinone may be used as a building block in controlled agrochemical and pharmaceutical synthesis. Suitability requires application-specific purity, impurity and regulatory evaluation.

Photographic Chemicals

Hydroquinone is traditionally used as a reducing agent and developer in photographic processing formulations.

Which Hydroquinone Grade Should You Choose?

Polymerization-Inhibitor Grade

Used for monomer stabilization and polymer-processing applications. Buyers should evaluate purity, color, oxidation products, melting range and solubility in the intended system.

Synthesis Grade

Suitable for organic synthesis and intermediate production. Related substances, moisture, metals and reaction consistency may require tighter control.

Photographic Grade

Photographic applications may require controlled purity, solution color, insoluble matter and reducing performance.

Pharmaceutical or Regulated Grade

A high assay alone does not demonstrate pharmaceutical suitability. Applicable manufacturing controls, impurity limits and regulatory documentation must also be confirmed.

Industrial Hydroquinone must not be promoted or used as a finished skin-lightening product.

Which Hydroquinone Specifications Should Buyers Compare?

Exact limits should be established in the purchasing specification rather than inferred from a general purity claim.

Why Can Hydroquinone Change Color?

Hydroquinone can oxidize when exposed to air, light, heat or contamination. This may produce yellow, brown or darker discoloration and oxidation products such as benzoquinone.

Color change does not automatically establish whether a batch passes or fails. The product should be evaluated against the agreed appearance, assay and impurity limits.

Packaging, Storage and Handling

Store Hydroquinone in a tightly closed container in a cool, dry and dark area. Protect it from air, moisture, heat and incompatible oxidizing materials. Inert-gas protection may be specified for certain products or packaging systems.

Avoid generating or inhaling dust. Use appropriate ventilation, protective gloves and eye protection, and consult the current Safety Data Sheet before handling.

Packaging options and storage conditions should be confirmed in the quotation.

Which Documents Should a Supplier Provide?

Buyers may request:

• Lot-specific Certificate of Analysis

• Safety Data Sheet

• Technical Data Sheet

• Approved specification

• Manufacturing and retest dates

• Country-of-origin information

• Packaging details

• Impurity or chromatographic information

• Regulatory statements required for the intended market

Pharmaceutical, cosmetic or other regulated-use claims should only be accepted when supported by verified documentation.

Why Source Hydroquinone from AOZUN?

AOZUN can help customers match Hydroquinone specifications with polymerization inhibition, antioxidant and synthesis applications.

For an accurate quotation, provide:

• Intended application

• Required assay and impurity limits

• Monomer or synthesis system

• Estimated quantity

• Preferred packaging

• Destination country

• Required quality or regulatory documents

Product origin, specification, packaging and document availability remain subject to the confirmed quotation.

Frequently Asked Questions

Is Hydroquinone organic or inorganic?

Hydroquinone is an organic aromatic compound belonging to the phenol family.

Is Hydroquinone a fine chemical or an intermediate?

It can be classified as both. Hydroquinone is a functional fine chemical when used as an inhibitor or antioxidant, and a chemical intermediate when used to manufacture dyes, stabilizers, agrochemicals or pharmaceutical compounds.

Are Hydroquinone and MEHQ the same?

No. Hydroquinone has CAS No. 123-31-9. MEHQ, or 4-methoxyphenol, has CAS No. 150-76-5. Their solubility, inhibitor performance and application conditions differ.

Does Hydroquinone require oxygen to inhibit polymerization?

Its inhibitor performance in many monomer systems depends partly on dissolved oxygen. The required oxygen level and inhibitor system must be established through application testing and process-safety review.

Why does stored Hydroquinone become yellow or brown?

Exposure to air, light, heat or contamination can cause oxidation and discoloration. Properly sealed, cool and dark storage helps reduce this change.

Can industrial Hydroquinone be used directly in skincare products?

No. Industrial material is not a finished cosmetic or medicine. Cosmetic and pharmaceutical uses are highly regulated and require the correct grade, manufacturing controls and market-specific authorization.

Request a Hydroquinone Quote

Contact AOZUN with your required grade, specification, application, quantity, packaging and destination. Our team will review the requirements and provide the appropriate product information and quotation.