Hydroquinone

CAS: 123-31-9

Overview

Hydroquinone (CAS 123-31-9 ), commonly abbreviated as HQ, is an aromatic diol used industrially as a polymerization inhibitor, antioxidant, and chemical intermediate. It prevents premature crosslinking in reactive monomers and protects unstable materials during storage.

In photographic and printing chemistry, HQ functions as a developing agent that reduces silver halide to metallic silver, controlling image density and contrast. Rubber and polymer manufacturers add it to acrylic and vinyl monomers during production.

This addition occurs during transport to suppress unwanted polymerization. As a pharmaceutical intermediate, it supports synthesis of active compounds and is used in topical formulations targeting skin hyperpigmentation for various medical applications.

Personal care formulators incorporate HQ into depigmentation products where it inhibits melanin synthesis, subject to regional regulatory limits. The compound is essential for maintaining the stability of sensitive chemical formulations.

Hydroquinone is supplied as a white crystalline powder in technical and pharmaceutical grades. USP and BP grades are available to meet compendial requirements for pharmaceutical and cosmetic applications globally.

Technical grade is standard for polymer stabilization and industrial chemical synthesis, typically packaged in fiber drums or multi-wall bags. This ensures the material remains stable and free from contaminants during long-term storage.

Physical Properties

Melting Point	170-171 °C
Boiling Point	285-287 °C
Density	1.332 g/cm³
Flash Point	165 °C
Appearance	white needle-like crystals or crystalline powder
Color	White to off-white
Odor	odorless
Form	Needle-Like Crystals or Crystalline Powder
Water Solubility	70 g/L (20 ºC)
Vapor Pressure	1 mm Hg ( 132 °C)
Refractive Index	1.6320
Log P	0.59 at 20℃

Safety & Handling

Danger GHS05 GHS07 GHS08 GHS09 Hazard Statements H302 Harmful if swallowed H312 Harmful in contact with skin H315 Causes skin irritation H316 Causes mild skin irritation H317 May cause an allergic skin reaction H318 Causes serious eye damage H319 Causes serious eye irritation H336 May cause drowsiness or dizziness H340 May cause genetic defects H341 Suspected of causing genetic defects H351 Suspected of causing cancer H360 May damage fertility or the unborn child H370 Causes damage to organs H372 Causes damage to organs through prolonged or repeated exposure H373 May causes damage to organs through prolonged or repeated exposure H400 Very toxic to aquatic life H410 Very toxic to aquatic life with long lasting effects H302+H312 Harmful if swallowed or in contact with skin Precautionary Statements P203 Obtain, consult and follow expert instructions for use. P260 Do not breathe dust/fume/gas/mist/vapours/spray. P261 Avoid breathing dust/fume/gas/mist/vapours/spray. P264 Wash … thoroughly after handling. P270 Do not eat, drink or smoke when using this product. P271 Use only outdoors or in a well-ventilated area. P272 Contaminated work clothing should not be allowed out of the workplace. P273 Avoid release to the environment. P280 Wear protective gloves/protective clothing/eye protection/face protection. P317 Get emergency medical help. P318 IF exposed or concerned, get medical advice. P319 Get medical advice/attention if you feel unwell. P321 Specific treatment (see … on this label). P330 Rinse mouth. P391 Collect spillage. P405 Store locked up. P501 Dispose of contents/container in accordance with local regulations. P264+P265 Wash … thoroughly after handling. P301+P317 Get emergency medical help. P302+P352 IF ON SKIN: Wash with plenty of water. P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing. P308+P316 Get emergency medical help immediately. P332+P317 Get emergency medical help. P333+P317 Get emergency medical help. P337+P317 If eye irritation persists: Get medical advice/attention. Get emergency medical help. P362+P364 Take off contaminated clothing and wash it before reuse. P403+P233 Store in a well-ventilated place. Keep container tightly closed. P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P305+P354+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.

Trade & Regulatory

HS Code	29072200
Storage Class	11 - Combustible Solids
WGK (Germany)	3

Other Names

Industries

Printing & Packaging Food & Nutrition Pharmaceuticals & Healthcare Personal Care & Cosmetics