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Home> Encyclopedia >   /  Benzene & Derivatives  /  Pharmaceutical Intermediates  /  Organic Intermediate
Hydroquinone structure
Hydroquinone structure

Hydroquinone

Iupac Name:benzene-1,4-diol
CAS No.: 123-31-9
Molecular Weight:110.11064
Modify Date.: 2022-11-25 02:12
Introduction: Light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption. View more+
1. Names and Identifiers
1.1 Name
Hydroquinone
1.2 Synonyms

1,4-benzenediol 1,4-Benzenediol,1,4-Dihydroxybenzene,HQ 1,4-dihydroxyanthone 1,4-dihydroxyanthron 1,4-Dihydroxybenzene 1,4-dihydroxy-benzene 1,4-Dihydroxy-benzol 1,4-Dihydroxy-xanthen-9-on 1,4-dihydroxy-xanthen-9-one 1,4-Dihydroxyxanthon 9H-Xanthen-9-one,1,4-dihydroxy AKOS BBS-00004220 EINECS 204-617-8 HYDROCHINONE hydroquinone--1,4-benzenediol HYDROXYQUINOL Idrochinone Melanex MFCD00002339 p-Benzenediol p-dihydroxybenzene p-hydroxy-PhOH

1.3 CAS No.
123-31-9
1.4 CID
785
1.5 EINECS(EC#)
204-617-8
1.6 Molecular Formula
C6H6O2 (isomer)
1.7 Inchi
InChI=1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
1.8 InChkey
QIGBRXMKCJKVMJ-UHFFFAOYSA-N
1.9 Canonical Smiles
C1=CC(=CC=C1O)O
1.10 Isomers Smiles
C1=CC(=CC=C1O)O
2. Properties
3.1 Density
1.332
3.1 Melting point
170-174℃
3.1 Boiling point
285-287℃
3.1 Refractive index
1.689
3.1 Flash Point
165℃
3.2 Precise Quality
110.03700
3.2 PSA
40.46000
3.2 logP
1.09780
3.2 Solubility
H2O: 50?mg/mL, clear
3.3 VaporDensity
3.81 (vs air)
3.4 Appearance
Hydroquinone appears as light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption.
3.5 Storage
Air Sensitive. Light Sensitive. Store under Argon. Ambient temperatures.
3.6 Autoignition Temperature
960 °F (USCG, 1999)
3.7 Carcinogenicity
No case reports of cancer associatedwith HQ exposure have been published.
3.8 Chemical Properties
white needle-like crystals or crystalline powder
3.9 Physical Properties
Colorless to pale brown, odorless, hexagonal crystals
3.10 Color/Form
White crystals
Monoclinic prisms (sublimation); needles from water; prisms from methanol
Light-tan, light-gray, or colorless crystals.
3.11 Contact Allergens
Hydroquinone is used in photography developers (blackand white, X-ray, and microfilms), in plastics, in hairdyes as an antioxidant and hair colorant. Hydroquinoneis found in many skin bleaching creams.
3.12 Heat of Combustion
-2.74X10+3 kJ/mol
3.13 Ionization Potential
7.95 eV
3.14 Odor
Odorless
3.15 pKa
10.35(at 20℃)
3.16 Water Solubility
H2O: 70 g/L (20 oC)
3.17 Spectral Properties
MAX ABSORPTION (WATER): 288 NM (LOG E= 3.36)
Index of refraction = 1.632 at 25 deg C
IR: 2882 (Coblentz Society Spectral Collection)
UV: 60 (Sadtler Research Laboratories Spectral Collection)
NMR: 10350 (Sadtler Research Laboratories Spectral Collection)
MASS: 1529 (NIST/EPA/MSDC Mass Spectral Database, 1990 version)
Intense mass spectral peaks: 81 m/z, 110 m/z
3.18 Stability
Stable. Combustible. Incompatible with strong oxidizing agents, strong bases, oxygen, ferric salts. Light and air-sensitive. Discolours in air.
3.19 StorageTemp
Store below +30°C.
3. Use and Manufacturing
4.1 Definition
ChEBI: A benzenediol comprising benzene core carrying two hydroxy substituents para to each other.
4.2 General Description
Light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption.
4.3 Produe Method
There are three current manufacturing processes for HQ:oxidative cleavage of diisopropylbenzene, oxidation of aniline,and hydroxylation of phenol.Diisopropylbenzene is air oxidized to the intermediatediisopropylbenzene bishydroperoxide. This hydroperoxideis purified by extraction and reacted further to formhydroquinone. The purified product is isolated by filtrationand packaged. The process can be almost entirely closed,continuous, computer-controlled, and monitored.HQcan also be prepared by oxidizing aniline to quinone inthe presence of manganese dioxide and sulfuric acid.p-Benzoquinone is then reduced to HQ using iron oxide.The resulting hydroquinone is crystallized and dried.The process occurs in a closed system.HQis also manufactured by hydroxylation of phenol usinghydrogen peroxide as a hydroxylation agent. The reaction iscatalyzed by strong mineral acids or ferrous or cobalt salts.
4.4 Purification Methods
Crystallise quinol from acetone, *benzene, EtOH, EtOH/*benzene, water or acetonitrile (25g in 30mL), preferably under nitrogen. Dry it under vacuum. [Wolfenden et al. J Am Chem Soc 109 463 1987, Beilstein 6 H 836, 6 IV 5712.] Hydroquinone Preparation Products And Raw materials Preparation Products
4.5 Usage
Use as photographic reducer and developer; as reagent in the determination of small quantities of phosphate; as antioxidant. Depigmentor
4. Safety and Handling
5.1 Symbol
GHS05;GHS07;GHS08;GHS09;
5.1 Hazard Codes
Xn
5.1 Signal Word
DANGER
5.1 Risk Statements
R22;R40;R41;R43;R50;R68
5.1 Safety Statements
S26;S36/37/39;S61
5.1 Exposure Standards and Regulations
Hydroquinone is an indirect food additive for use only as a component of adhesives.
5.2 Packing Group
III
5.2 Octanol/Water Partition Coefficient
log Kow = 0.59
5.3 Fire Hazard
Dust cloud may explode if ignited in an enclosed area. Hydroquinone can react with oxidizing materials and is rapidly oxidized in the presence of alkaline materials. Oxidizes in air.
5.4 Other Preventative Measures
Work clothing that becomes wet or significantly contaminated should be removed and replaced.
Workers whose clothing may have become contaminated should change into uncontaminated clothing before leaving the work premises.
The worker should immediately wash the skin when it becomes contaminated.
HYDROQUINONE SHOULD BE HANDLED WITH CAUTION. CONTACT WITH EYES OR INHALATION OF ITS DUST OR VAPORS, PARTICULARLY WHEN LIBERATED @ ELEVATED TEMP, MUST BE AVOIDED.
SRP: The scientific literature for the use of contact lenses in industry is conflicting. The benefit or detrimental effects of wearing contact lenses depend not only upon the substance, but also on factors including the form of the substance, characteristics and duration of the exposure, the uses of other eye protection equipment, and the hygiene of the lenses. However, there may be individual substances whose irritating or corrosive properties are such that the wearing of contact lenses would be harmful to the eye. In those specific cases, contact lenses should not be worn. In any event, the usual eye protection equipment should be worn even when contact lenses are in place.
SRP: Local exhaust ventilation should be applied wherever there is an incidence of point source emissions or dispersion of regulated contaminants in the work area. Ventilation control of the contaminant as close to its point of generation is both the most economical and safest method to minimize personnel exposure to airborne contaminants.
If material not on fire and not involved in fire: Keep material out of water sources and sewers. Build dikes to contain flow as necessary. Attempt to stop leak if without undue personnel hazard.
Personnel protection: Keep upwind. Avoid breathing vapors. ... If contact with the material anticipated, wear appropriate chemical protective clothing.
SRP: Contaminated protective clothing should be segregated in such a manner so that there is no direct personal contact by personnel who handle, dispose, or clean the clothing. Quality assurance to ascertain the completeness of the cleaning procedures should be implemented before the decontaminated protective clothing is returned for reuse by the workers. Contaminated clothing should not be taken home at end of shift, but should remain at employee's place of work for cleaning.
SRP: Wastewater from contaminant suppression, cleaning of protective clothing/equipment, or contaminated sites should be contained and evaluated for subject chemical or decomposition product concentrations. Concentrations shall be lower than applicable environmental discharge or disposal criteria. Alternatively, pretreatment and/or discharge to a POTW is acceptable only after review by the governing authority. Due consideration shall be given to remediation worker exposure (inhalation, dermal and ingestion) as well as fate during treatment, transfer and disposal. If it is not practicable to manage the chemical in this fashion, it must meet Hazardous Material Criteria for disposal.
5.5 Hazard Class
9
5.5 Hazard Declaration
H302; H317; H318; H341; H351; H410
5.5 Cleanup Methods
/SRP: If time permits, pits, ponds, lagoons, soak holes, or holding areas should be sealed with an impermeable flexible membrane liner./Environmental Considerations: Land spill Dig a pit, pond, lagoon, holding area to contain liquid or solid material. Cover solids with a plastic sheet to prevent dissolving in rain or fire fighting water. Dike surface flow using soil, sand bags, foamed polyurethane, or foamed concrete. Absorb bulk liquid with fly ash, cement powder, or commercial sorbents.
Environmental Considerations: Water spill Use natural barriers or oil spill control booms to limit spill travel. Use natural deep water pockets, excavated lagoons, or sand bag barriers to trap material at bottom. Remove trapped material with suction hoses.
Environmental Considerations: Air spill Apply water spray or mist to knock down vapors.
5.6 DisposalMethods
SRP: At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.
The following wastewater treatment technologies have been investigated for Hydroquinone: Concentration process: Reverse osmosis.
The following wastewater treatment technologies have been investigated for Hydroquinone: Concentration process: Activated carbon.
Hydroquinone is a waste chemical stream constituent which may be subjected to ultimate disposal by controlled incineration.
5.7 DOT Emergency Guidelines
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Health: TOXIC; inhalation, ingestion, or skin contact with material may cause severe injury or death. Contact with molten substance may cause severe burns to skin and eyes. Avoid any skin contact. Effects of contact or inhalation may be delayed. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Fire or Explosion: Combustible material: may burn but does not ignite readily. When heated, vapors may form explosive mixtures with air: indoors, outdoors, and sewers explosion hazards. Those substances designated with a "P" may polymerize explosively when heated or involved in a fire. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Public Safety: CALL Emergency Response Telephone Number ... As an immediate precautionary measure, isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters (75 feet) for solids. Keep unauthorized personnel away. Stay upwind. Keep out of low areas. Ventilate enclosed areas.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Protective Clothing: Wear positive pressure self-contained breathing apparatus (SCBA). Wear chemical protective clothing that is specifically recommended by the manufacturer. It may provide little or no thermal protection. Structural firefighters' protective clothing provides limited protection in fire situations ONLY; it is not effective in spill situations where direct contact with the substance is possible.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Evacuation: ... Fire: If tank, rail car or tank truck is involved in a fire, ISOLATE for 800 meters (1/2 mile) in all directions; also, consider initial evacuation for 800 meters (1/2 mile) in all directions.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Fire: Small fires: Dry chemical, CO2 or water spray. Large fires: Dry chemical, CO2, alcohol-resistant foam or water spray. Move containers from fire area if you can do it without risk. Dike fire control water for later disposal; do not scatter the material. Fire involving tanks or car/trailer loads: Fight fire from maximum distance or use unmanned hose holders or monitor nozzles. Do not get water inside containers. Cool containers with flooding quantities of water until well after fire is out. Withdraw immediately in case of rising sound from venting safety devices or discoloration of tank. ALWAYS stay away from tanks engulfed in fire.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ Spill or Leak: ELIMINATE all ignition sources (no smoking, flares, sparks or flames in immediate area). Do not touch damaged containers or spilled material unless wearing appropriate protective clothing. Stop leak if you can do it without risk. Prevent entry into waterways, sewers, basements or confined areas. Absorb or cover with dry earth, sand or other non-combustible material and transfer to containers. DO NOT GET WATER INSIDE CONTAINERS.
/GUIDE 153: SUBSTANCES - TOXIC AND/OR CORROSIVE (COMBUSTIBLE)/ First Aid: Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves.
5.8 RIDADR
UN 2662
5.8 Fire Fighting Procedures
TO FIGHT FIRE, USE WATER, CARBON DIOXIDE, DRY CHEM ... .
If material on fire or involved in fire: Extinguish fire using agent suitable for type of surrounding fire. (Material itself does not burn or burns with difficulty.) Use water in flooding quantities as fog. Apply water from as far a distance as possible. Keep run-off water out of sewers and water sources.
Water or foam may cause frothing. Alcohol foam.
5.9 FirePotential
FIRE HAZARD: SLIGHT, WHEN EXPOSED TO HEAT OR FLAME; CAN REACT WITH OXIDIZING MATERIALS.
5.10 Caution Statement
P273-P280-P305 + P351 + P338-P501
5.10 Formulations/Preparations
... AVAILABLE IN US IN PHOTOGRAPHIC & TECHNICAL GRADES; SPECIFICATIONS FOR TECHNICAL GRADE ARE: APPEARANCE, LIGHT-TAN TO LIGHT GRAY CRYSTALS; 98.5% MIN ACTIVE INGREDIENT; 1% MAX WATER; 0.07% MAX ASH; MP OF 169 DEC C MIN; & MISCIBLE WITH WATER ... .
IN JAPAN, COMMERCIALLY AVAILABLE HYDROQUINONE HAS 99% MIN ACTIVE INGREDIENT; 0.05% MAX IGNITION RESIDUE; 30 MG/KG MAX LEAD; 30 MG/KG MAX IRON; & MP OF 169-174 DEG C.
Preparations: (AHFS, 2009) Hydroquinone preparations: Routes Dosage Forms Strength Brand Names Topical Cream 1.5% Esoterica Sensitive Skin (with parabens and sodium bisulfite); Medicis 2% Eldopaque (with sodium metabisulfite in an opaque base); Valeant 2% Eldoquin (with sodium metabisulfite); Valeant 2% Esoterica Regular (with parabens, propylene glycol, and sodium bisulfite); Medicis 4% Eldopaque Forte (with propylene glycol and sodium metabisulfite in an opaque base); Valeant 4% Eldoquin Forte (with propylene glycol propylparaben and sodium metabisulfite); Valeant 4% Hydroquinone Cream Ethex, Glades 4% Melpaque HP (with sodium metabisulfite in an opaque talc base); Stratus 4% Melquin HP (with propylparaben and sodium metabisulfite); Stratus Solution 3% Melanex (with SD alcohol 40 45% isopropyl alcohol 4% and propylene glycol); Neutrogena 3% Melquin-3 (with SD alcohol 45% isopropyl alcohol 4% and propylene glycol); Stratus 3% Hydroquinone Solution (with SD alcohol 45% isopropyl alcohol 4% and propylene glycol); Glades
Skin bleaching stick containing hydroquinone.
5.11 WGK Germany
3
5.11 RTECS
MX3500000
5.11 Protective Equipment and Clothing
Wear appropriate personal protective clothing to prevent skin contact.
Wear appropriate eye protection to prevent eye contact.
Eyewash fountains should be provided in areas where there is any possbility that workers could be exposed to the substance; this is irrespective of the recommendation involving the wearing of eye protection. (>7%)
Respirator Recommendations: Up to 50 mg/cu m Assigned Protection Factor (APF) Respirator Recommendation APF = 25 Any powered air-purifying respirator with a high-efficiency particulate filter. Substance causes eye irritation or damage; eye protection needed. APF = 50 Any air-purifying, full-facepiece respirator with an N100, R100, or P100 filter. APF = 50 Any supplied-air respirator that has a tight-fitting facepiece and is operated in a continuous-flow mode. Substance causes eye irritation or damage; eye protection needed. APF = 50 Any self-contained breathing apparatus with a full facepiece. APF = 50 Any supplied-air respirator with a full facepiece.
Respirator Recommendations: Emergency or planned entry into unknown concentrations or IDLH conditions: Assigned Protection Factor (APF) Respirator Recommendation APF = 10,000 Any self-contained breathing apparatus that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode. APF = 10,000 Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained positive-pressure breathing apparatus.
Respirator Recommendations: Escape conditions: Assigned Protection Factor (APF) Respirator Recommendation APF = 50 Any air-purifying, full-facepiece respirator with an N100, R100, or P100 filter./Any appropriate escape-type, self-contained breathing apparatus.
5.12 Reactivities and Incompatibilities
Strong oxidizers, alkalis.
Accidental mixing of the hot crude hydroquinone with concn sodium hydroxide solution led to extensive exothermic decomposition.
Violent reaction with NaOH.
5.13 Report

IARC Cancer Review: Group 3 IMEMDT ?? IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 7 , 1987,p. 56.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.:?) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) ; Animal Inadequate Evidence IMEMDT ?? IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 15 , 1977,p. 155.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.:?) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) . Community Right-To-Know List. EPA Extremely Hazardous Substances List. EPA Genetic Toxicology Program. Reported in EPA TSCA Inventory.

5.14 Skin, Eye, and Respiratory Irritations
Irritating to eyes, skin, and resp system.
The inhalation of vapors, particularly when liberated at high temperatures, must be avoided.
Hydroquinone/ dust is irritating to eyes, nose, and mucous membranes.
5.15 Safety

Safety Information of Hydroquinone (CAS NO.123-31-9):
Hazard Codes: XnHarmful,NDangerous
Risk Statements: 22-40-41-43-50-68??
R22:Harmful if swallowed.?
R40:Limited evidence of a carcinogenic effect.?
R41:Risk of serious damage to the eyes.?
R50:Very toxic to aquatic organisms.?
R68:Possible risk of irreversible effects.
Safety Statements: 26-36/37/39-61
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.?
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection.?
S61:Avoid release to the environment. Refer to special instructions / safety data sheets.
RIDADR: 2662
WGK Germany: 3
RTECS: MX3500000
HazardClass: 9
PackingGroup: III

5.16 Specification

?Hydroquinone , its CAS NO. is 123-31-9, the synonyms are Quinol ; 1,4-Benzenediol ; 1,4-Dihydroxybenzene .

5.17 Toxicity
LD50 orally in rats: 320 mg/kg (Woodard)
5. MSDS

2.Hazard identification

2.1 Classification of the substance or mixture

Acute toxicity - Oral, Category 4

Serious eye damage, Category 1

Skin sensitization, Category 1

Germ cell mutagenicity, Category 2

Carcinogenicity, Category 2

Hazardous to the aquatic environment, short-term (Acute) - Category Acute 1

2.2 GHS label elements, including precautionary statements

Pictogram(s)
Signal word

Danger

Hazard statement(s)

H302 Harmful if swallowed

H318 Causes serious eye damage

H317 May cause an allergic skin reaction

H341 Suspected of causing genetic defects

H351 Suspected of causing cancer

H400 Very toxic to aquatic life

Precautionary statement(s)
Prevention

P264 Wash ... thoroughly after handling.

P270 Do not eat, drink or smoke when using this product.

P280 Wear protective gloves/protective clothing/eye protection/face protection.

P261 Avoid breathing dust/fume/gas/mist/vapours/spray.

P272 Contaminated work clothing should not be allowed out of the workplace.

P201 Obtain special instructions before use.

P202 Do not handle until all safety precautions have been read and understood.

P273 Avoid release to the environment.

Response

P301+P312 IF SWALLOWED: Call a POISON CENTER/doctor/\u2026if you feel unwell.

P330 Rinse mouth.

P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.

P310 Immediately call a POISON CENTER/doctor/\u2026

P302+P352 IF ON SKIN: Wash with plenty of water/...

P333+P313 If skin irritation or rash occurs: Get medical advice/attention.

P321 Specific treatment (see ... on this label).

P362+P364 Take off contaminated clothing and wash it before reuse.

P308+P313 IF exposed or concerned: Get medical advice/ attention.

P391 Collect spillage.

Storage

P405 Store locked up.

Disposal

P501 Dispose of contents/container to ...

2.3 Other hazards which do not result in classification

none

9. Other Information
9.0 Merck
14,4808
9.1 BRN
605970
9.2 Description
Hydroquinone (HQ) is produced by the oxidation of aniline or phenol, by the reduction of quinone, or from a reaction of acetylene and carbon monoxide. Hydroquinone occurs naturally as a glucose ether, also known as arbutin, in the leaves of many plants and in fruits, as well as one of the agents used in the defense mechanism of the bombardier beetle, family Carabidae.
9.3 Chemical Properties
white needle-like crystals or crystalline powder
9.4 Chemical Properties
Hydroquinone, a colorless, hexagonal prism, has been reported to be a good antimitotic and tumor-inhibiting agent. It is a reducing agent used in a photographic developer, which polymerizes in the presence of oxidizing agents. In the manufacturing industry it may occur include bacteriostatic agent, drug, fur processing, motor fuel, paint, organic chemicals, plastics, stone coating, and styrene monomers.
9.5 Physical properties
Colorless to pale brown, odorless, hexagonal crystals
9.6 Originator
Quinnone,Dermohr,US,1980
9.7 Uses
Use as photographic reducer and developer; as reagent in the determination of small quantities of phosphate; as antioxidant. Depigmentor
9.8 Uses
hydroquinone is a pigment-lightening agent used in bleaching creams. Hydroquinone combines with oxygen very rapidly and becomes brown when exposed to air. Although it occurs naturally, the synthetic version is the one commonly used in cosmetics. Application to the skin may cause allergic reaction and increase skin sun sensitivity. Hydroquinone is potentially carcinogenic and is associated with causing ochronosis, a discoloration of the skin. The u.S. FDA has banned hydroquinone from oTC cosmetic formulations, but allows 4 percent in prescription products. Its use in cosmetics is prohibited in some european countries and in Australia.
9.9 Uses
K channel agonist, antihypertensive
9.10 Uses
reducing agent prevents polymerization of resin monomers lightens darkened skin, light sensitive
9.11 Uses
Photographic reducer and developer; antioxidant; stabilizing agent for some polymers; intermediate in the manufacturing of some dyes and pigments; in cosmetic formulations.
9.12 Definition
ChEBI: A benzenediol comprising benzene core carrying two hydroxy substituents para to each other.
9.13 Indications
Hydroquinone interferes with the production of the pigment melanin by epidermal melanocytes through at least two mechanisms: it competitively inhibits tyrosinase, one of the principal enzymes responsible for converting tyrosine to melanin, and it selectively damages melanocytes and melanosomes (the organelles within which melanin is stored).
9.14 Production Methods
There are three current manufacturing processes for HQ: oxidative cleavage of diisopropylbenzene, oxidation of aniline, and hydroxylation of phenol.
Diisopropylbenzene is air oxidized to the intermediate diisopropylbenzene bishydroperoxide. This hydroperoxide is purified by extraction and reacted further to form hydroquinone. The purified product is isolated by filtration and packaged. The process can be almost entirely closed, continuous, computer-controlled, and monitored.
HQcan also be prepared by oxidizing aniline to quinone in the presence of manganese dioxide and sulfuric acid. p-Benzoquinone is then reduced to HQ using iron oxide. The resulting hydroquinone is crystallized and dried. The process occurs in a closed system.
HQis also manufactured by hydroxylation of phenol using hydrogen peroxide as a hydroxylation agent. The reaction is catalyzed by strong mineral acids or ferrous or cobalt salts.
9.15 Manufacturing Process
Into a pressure reactor there was charged 100 ml of methanol and 1 g of diruthenium nonacarbonyl. The reactor was closed, cooled in solid carbon dioxide/acetone, and evacuated. Acetylene, to the extent of 1 mol (26 g), was metered into the cold reactor. Carbon monoxide was then pressured into this vessel at 835-980 atmospheres, during a period of 16.5 hours; while the reactor was maintained at 100°C to 150°C. The reactor was then cooled to room temperature and opened.
The reaction mixture was removed from the vessel and distilled at a pressure of 30-60 mm, and a bath temperature of 30°C to 50°C until the methanol had all been removed. The extremely viscous tarry residue remaining in the still pot was given a very crude distillation, the distillate boiling at 82°C to 132°C/2 mm. In an attempt to purify this distillate by a more careful distillation, 5.3 g of a liquid distilling from 53°C to 150°C/5 mm was collected. At this point, much solid sublimate was noted not only in this distillate but in the condenser of the still. 7 g of the solid sublimate was scraped out of the condenser of the still. Recrystallization of the sublimate from ethyl acetate containing a small amount of petroleum ether gave beautiful crystals melting at 175°C to 177°C (5 g). Infrared analysis confirmed that this compound was hydroquinone (9% conversion).
9.16 Brand name
Aida;Ambi- skin tone;Black and white;Creme des 3 fleur d'orient;Eldopaque forte;Eldoquin forte 4% cream;Epocler;Esoterica facial;Esoterica regular;Esoterica sensitive skin;Esoterica sunscreen;Melanex topical sollution;Melpaque hp;Melqui hp;Neostrata aha gel;Neostrata hq;Nuquin hp;Pigmanorm;Porcelana;Sinquin;Solaquin forte sun bleaching;Superfade age spot;Ultraquin plaine.
9.17 Therapeutic Function
Depigmentor
9.18 World Health Organization (WHO)
Hydroquinone was introduced in 1965 as a topical depigmenting agent for hyperpigmentation. At high concentrations hydroquinone is corrosive and in most countries has been restricted to the level of approximately 2% and limited to the period of less than 2 months. Additional consideration for restrictive action is that animal experiments have also demonstrated carcinogenic and mutagenic potential of hydroquinone.
9.19 Synthesis Reference(s)
Chemistry Letters, 14, p. 731, 1985
The Journal of Organic Chemistry, 50, p. 1722, 1985
Tetrahedron Letters, 22, p. 2337, 1981 DOI: 10.1016/S0040-4039(01)82900-2
9.20 General Description
Light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption.
9.21 Air & Water Reactions
Darkens on exposure to air and light. Miscible in water. Solutions become brown in air due to oxidation. Oxidation is very rapid in the presence of alkali.
9.22 Reactivity Profile
Hydroquinone is a slight explosion hazard when exposed to heat. Incompatible with strong oxidizing agents. Also incompatible with bases. Hydroquinone reacts with oxygen and sodium hydroxide. Reacts with ferric salts . Hot and/or concentrated NaOH can cause Hydroquinone to decompose exothermically at elevated temperature. (NFPA Pub. 491M, 1975, 385)
9.23 Hazard
Toxic by ingestion and inhalation, irritant. Questionable carcinogen.
9.24 Health Hazard
Exposures to hydroquinone in large quantities by accidental oral ingestion produce toxicity and poisoning. The symptoms of poisoning include, but are not limited to, blurred speech, tinnitus, tremors, sense of suffocation, vomiting, muscular twitching, headache, convul- sions, dyspnea and cyanosis from methemoglobinemia, coma, and collapse from respira- tory failure. Occupational workers should be allowed to work with protective clothing and dust masks with full-face or goggles to protect the eyes, and under proper management.
9.25 Health Hazard
Hydroquinone is very toxic; the probable oral lethal dose for humans is 50-500 mg/kg, or between 1 teaspoon and 1 ounce for a 150 lb. person. It is irritating but not corrosive. Fatal human doses have ranged from 5-12 grams, but 300-500 mg have been ingested daily for 3-5 months without ill effects. Death is apparently initiated by respiratory failure or anoxia.
9.26 Fire Hazard
Dust cloud may explode if ignited in an enclosed area. Hydroquinone can react with oxidizing materials and is rapidly oxidized in the presence of alkaline materials. Oxidizes in air.
9.27 Contact allergens
Hydroquinone is used in photography developers (black and white, X-ray, and microfilms), in plastics, in hair dyes as an antioxidant and hair colorant. Hydroquinone is found in many skin bleaching creams.
9.28 Clinical Use
Hydroquinone is applied topically to treat disorders characterized by excessive melanin in the epidermis, such as melasma. In the United States, nonprescription skin-lightening products contain hydroquinone at concentrations of 2% or less; higher concentrations are available by prescription.
9.29 Side effects
The incidence of adverse effects with hydroquinone increases in proportion to its concentration. A relatively common side effect is local irritation, which may actually exacerbate the discoloration of the skin being treated. Allergic contact dermatitis occurs less commonly. A rare but more serious complication is exogenous ochronosis, in which a yellow-brown pigment deposited in the dermis results in blue-black pigmentation of the skin that may be permanent.
9.30 Carcinogenicity
No case reports of cancer associated with HQ exposure have been published.
9.31 Source
Hydroquinone occurs naturally in strawberry tree leaves, pears, blackberries, Chinese alpenrose, bilberries, blackberries, hyacinth flowers, anise, cowberries, and lingonberries (Duke, 1992).
9.32 Environmental fate
Biological. In activated sludge, 7.5% mineralized to carbon dioxide after 5 d (Freitag et al., 1985). Under methanogenic conditions, inocula from a municipal sewage treatment plant digester degraded hydroquinone to phenol prior to being mineralized to carbon dioxide and methane (Young and Rivera, 1985). In various pure cultures, hydroquinone degraded to the following intermediates: benzoquinone, 2-hydroxy-1,4-benzoquinone, and β-ketoadipic acid. Hydroquinone also degraded in activated sludge but no products were identified (Harbison and Belly, 1982). Heukelekian and Rand (1955) reported a 5-d BOD value of 0.74 g/g which is 39.2% of the ThOD value of 1.89 g/g. In activated sludge inoculum, following a 20-d adaptation period, 90.0% COD removal was achieved. The average rate of biodegradation was 54.2 mg COD/g?h (Pitter, 1976).
Photolytic. A carbon dioxide yield of 53.7% was achieved when hydroquinone adsorbed on silica gel was irradiated with light (λ >290 nm) for 17 h (Freitag et al., 1985). Chemical/Physical. Ozonolysis products reported are p-quinone and dibasic acids (Verschueren, 1983). Moussavi (1979) studied the autoxidation of hydroquinone in slightly alkaline (pH 7 to 9) aqueous solutions at room temperature. The oxidation of hydroquinone by oxygen followed first-order kinetics that yielded hydrogen peroxide and p-quinone as products. At pH values of 7.0, 8.0, and 9.0, the calculated half-lives of this reaction were 111, 41, and 0.84 h, respectively (Moussavi, 1979).
Chlorine dioxide reacted with hydroquinone in an aqueous solution forming p-benzoquinone (Wajon et al., 1982). Kanno et al. (1982) studied the aqueous reaction of hydroquinone and other substituted aromatic hydrocarbons (aniline, toluidine, 1- and 2-naphthylamine, phenol, cresol, pyrocatechol, resorcinol, and 1-naphthol) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. As the pH was lowered, the amount of cyanogen chloride formed increased (Kanno et al., 1982).
At influent concentrations of 1.0, 0.1, 0.01, and 0.001 mg/L, the GAC adsorption capacities were 160, 90, 51, and 29 mg/g, respectively (Dobbs and Cohen, 1980).
9.33 Purification Methods
Crystallise quinol from acetone, *benzene, EtOH, EtOH/*benzene, water or acetonitrile (25g in 30mL), preferably under nitrogen. Dry it under vacuum. [Wolfenden et al. J Am Chem Soc 109 463 1987, Beilstein 6 H 836, 6 IV 5712.]
9.34 Toxicity evaluation
Benzene, phenol, and hydroquinone are metabolized in vivo to benzoquinone and excreted as the mercapturate, N-acetyl-S- (2,5-dihydroxyphenyl)-L-cysteine. Hydroquinone is a reducing cosubstrate for peroxidase enzymes, and the resultant semiquinone and p-benzoquinone may bind to DNA.
9.35 Usage
Hydroquinone is used as a reducing agent and finds applications in black and white photographic developers for film and paper along with 4-(methylamino)phenol sulfate (metol). In this application, silver halides are reduced to elemental silver. It acts as a polymerization inhibitor which prevents polymerization of acrylic acid, methyl methacrylate, cyanoacrylate and other monomers. It undergoes mild oxidation to convert into parabenzoquinone. It is also used as an intermediate to produce antioxidants for rubber and food.
9.36 Storage features
Separated from strong bases and food and feedstuffs.
10. Computational chemical data
  • Molecular Weight: 110.11064g/mol
  • Molecular Formula: C6H6O2
  • Compound Is Canonicalized: True
  • XLogP3-AA: null
  • Exact Mass: 110.036779430
  • Monoisotopic Mass: 110.036779430
  • Complexity: 54.9
  • Rotatable Bond Count: 0
  • Hydrogen Bond Donor Count: 2
  • Hydrogen Bond Acceptor Count: 2
  • Topological Polar Surface Area: 40.5
  • Heavy Atom Count: 8
  • Defined Atom Stereocenter Count: 0
  • Undefined Atom Stereocenter Count: 0
  • Defined Bond Stereocenter Count: 0
  • Undefined Bond Stereocenter Count: 0
  • Isotope Atom Count: 0
  • Covalently-Bonded Unit Count: 1
  • CACTVS Substructure Key Fingerprint: AAADcYBgMAAAAAAAAAAAAAAAAAAAAAAAAAAwAAAAAAAAAAABAAAAGgAACAAACASAkAAwBoAAAgCAACBCAAACAAAgIAAIiAAGCIgIJiKCERKAcAAkwBEImAfAQAAAAQAAAAAAAAACAAAAAAAAAAAAAAAAAA==
11. Question & Answer
  • Hydroquinone is a known carcinogen at concentrations greater than 1%. I would NOT recommend using it on your lips or anywhere else on your body.
  • I would not use either one, both are dangerous. Mercury is toxic and bad for the environment. Hydroquinone has many side effects and reacts with other drugs. Check with your medical professional before using anything.
  • What resonance forms stabilize deprotonated hydroquinone? Deprotonated hydroquinone looks like this: Possible resonance forms include: 1 and 2 look reasonable: they don't carry multiple charges. My question is: how much do these two structures contribute to the stability of deprotonated hydroquinon...
  • This is benzene-1,4-diol. Its common name is quinol and hydroquinone. How is hydroquinone an accepted name since the functional group here is an alcohol and not a ketone? Is this the only such case or does it apply elsewhere too? This is benzene-1,2,4-triol also known as hydroxyquinol. How does the...
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