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HQ (HYDROQUINONE)

CAS Number : 123-31-9
EC Number  : 204-617-8
PubChem CID : 785
ECHA InfoCard    : 100.004.199 
ChemSpider    : 764 
Chemical formula : C6H6O2
Molar mass     : 110.112 g·mol−1
Density             : 1.3 g cm−3, solid
Melting point     : 172 °C

Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. Hydroquinone has two hydroxyl groups bonded to a benzene ring in a para position. 
Hydroquinone is a white granular solid. 
Substituted derivatives of this parent compound are also referred to as hydroquinones. 
The name "hydroquinone" was coined by Friedrich Wöhler in 1843.

Hydroquinone is a white crystalline strongly reducing phenol C6H6O2 used especially as a photographic developer, as an antioxidant and stabilizer, and in medicine to remove pigmentation from hyperpigmented areas of skin.
Hydroquinone is a white crystalline substance when pure and is highly soluble in water. 
Hydroquinone is combustible when preheated. 
Hydroquinone is a reducing agent that is reversibly oxidized to semiquinone and quinone.

Production of Hydroquinone
Hydroquinone is produced industrially by two main routes.
The most widely used route is similar to the cumene process in reaction mechanism and involves the dialkylation of benzene with propene to give 1,4-diisopropylbenzene. 
This compound reacts with air to afford the bis(hydroperoxide), which is structurally similar to cumene hydroperoxide and rearranges in acid to give acetone and hydroquinone.
A second route involves hydroxylation of phenol over a catalyst. 
The conversion uses hydrogen peroxide and affords a mixture of hydroquinone and its ortho isomer catechol (benzene-1,2-diol):
C6H5OH + H2O2 → C6H4(OH)2 + H2O
Other, less common methods include:

A potentially significant synthesis of hydroquinone from acetylene and iron pentacarbonyl has been proposed Iron pentacarbonyl serves as a catalyst, rather than as a reagent, in the presence of free carbon monoxide gas. 
Rhodium or ruthenium can substitute for iron as the catalyst with favorable chemical yields but are not typically used due to their cost of recovery from the reaction mixture.
Hydroquinone and its derivatives can also be prepared by oxidation of various phenols. 
Examples include Elbs persulfate oxidation and Dakin oxidation.
Hydroquinone was first obtained in 1820 by the French chemists Pelletier and Caventou via the dry distillation of quinic acid.

Reactions of Hydroquinone
The reactivity of hydroquinone's hydroxyl groups resembles that of other phenols, being weakly acidic. 
The resulting conjugate base undergoes easy O-alkylation to give mono- and diethers. 
Similarly, hydroquinone is highly susceptible to ring substitution by Friedel–Crafts reactions such as alkylation. 
This reaction is exploited en route to popular antioxidants such as 2-tert-butyl-4-methoxyphenol (BHA). 
The useful dye quinizarin is produced by diacylation of hydroquinone with phthalic anhydride.

Redox
Hydroquinone undergoes oxidation under mild conditions to give benzoquinone. 
This process can be reversed. 
Some naturally occurring hydroquinone derivatives exhibit this sort of reactivity, one example being coenzyme Q. 
Industrially this reaction is exploited both with hydroquinone itself but more often with its derivatives where one OH has been replaced by an amine.
When colorless hydroquinone and benzoquinone, a bright yellow solid, are cocrystallized in a 1:1 ratio, a dark-green crystalline charge-transfer complex (melting point 171 °C) called quinhydrone (C6H6O2·C6H4O2) is formed. 
This complex dissolves in hot water, where the two molecules dissociate in solution.

Amination
An important reaction is the conversion of hydroquinone to the mono- and diamine derivatives. Methylaminophenol, used in photography, is produced in this way:
C6H4(OH)2 + CH3NH2 → HOC6H4NHCH3 + H2O
Diamines, useful in the rubber industry as antiozone agents, are similarly produced from aniline:
C6H4(OH)2 + 2 C6H5NH2 → C6H4(N(H)C6H5)2 + 2 H2O

Uses of Hydroquinone
Hydroquinone has a variety of uses principally associated with its action as a reducing agent that is soluble in water. 
It is a major component in most black and white photographic developers for film and paper where, with the compound metol, it reduces silver halides to elemental silver.
There are various other uses associated with its reducing power. 

As a polymerisation inhibitor, exploiting its antioxidant properties, hydroquinone prevents polymerization of acrylic acid, methyl methacrylate, cyanoacrylate, and other monomers that are susceptible to radical-initiated polymerization. 
By acting as a free radical scavenger, hydroquinone serves to prolong the shelflife of light-sensitive resins such as preceramic polymers.
Hydroquinone can lose a hydrogen cation from both hydroxyl groups to form a diphenolate ion. 
The disodium diphenolate salt of hydroquinone is used as an alternating comonomer unit in the production of the polymer PEEK.

Skin depigmentation of Hydroquinone 
Hydroquinone is used as a topical application in skin whitening to reduce the color of skin. 
It does not have the same predisposition to cause dermatitis as metol does. 
This is a prescription-only ingredient in some countries, including the member states of the European Union under Directives 76/768/EEC:1976.

In 2006, the United States Food and Drug Administration revoked its previous approval of hydroquinone and proposed a ban on all over-the-counter preparations.
The FDA officially banned hydroquinone in 2020 as part of a larger reform of the over-the-counter drug review process.
The FDA stated that hydroquinone cannot be ruled out as a potential carcinogen.
This conclusion was reached based on the extent of absorption in humans and the incidence of neoplasms in rats in several studies where adult rats were found to have increased rates of tumours, including thyroid follicular cell hyperplasias, anisokaryosis (variation in nuclei sizes), mononuclear cell leukemia, hepatocellular adenomas and renal tubule cell adenomas. 
The Campaign for Safe Cosmetics has also highlighted concerns.

Numerous studies have revealed that hydroquinone, if taken orally, can cause exogenous ochronosis, a disfiguring disease in which blue-black pigments are deposited onto the skin; however, skin preparations containing the ingredient are administered topically. 
The FDA had classified hydroquinone in 1982 as a safe product - generally recognized as safe and effective (GRASE), however additional studies under the National Toxicology Program (NTP) were suggested in order to determine whether there is a risk to humans from the use of hydroquinone.
NTP evaluation showed some evidence of long-term carcinogenic and genotoxic effects.

While using hydroquinone as a lightening agent can be effective with proper use, it can also cause skin sensitivity. 
Using a daily sunscreen with a high PPD (persistent pigment darkening) rating reduces the risk of further damage. 
Hydroquinone is sometimes combined with alpha-hydroxy acids that exfoliate the skin to quicken the lightening process. 
In the United States, topical treatments usually contain up to 2% in hydroquinone. Otherwise, higher concentrations (up to 4%) should be prescribed and used with caution.

While hydroquinone remains widely prescribed for treatment of hyperpigmentation, questions raised about its safety profile by regulatory agencies in the EU, Japan, and USA encourage the search for other agents with comparable efficacy.
Several such agents are already available or under research,including azelaic acid, kojic acid, retinoids, cysteamine, topical steroids, glycolic acid, and other substances. 
One of these, 4-butylresorcinol, has been proven to be more effective at treating melanin-related skin disorders by a wide margin, as well as safe enough to be made available over the counter.

Natural occurrences of Hydroquinone
Hydroquinones are one of the two primary reagents in the defensive glands of bombardier beetles, along with hydrogen peroxide (and perhaps other compounds, depending on the species), which collect in a reservoir. 
The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. 
This chamber is lined with cells that secrete catalases and peroxidases. 
When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones. 
These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it, producing a hot spray from the beetle's abdomen.

Farnesyl hydroquinone derivatives are the principal irritants exuded by the poodle-dog bush, which can cause severe contact dermatitis in humans.
Hydroquinone is thought to be the active toxin in Agaricus hondensis mushrooms.
Hydroquinone has been shown to be one of the chemical constituents of the natural product propolis.
Hydroquinone is also one of the chemical compounds found in castoreum. 
This compound is gathered from the beaver's castor sacs.
In bearberry (Arctostaphylos uva-ursi), arbutin is converted to hydroquinone.

Hydroquinone is produced as an inhibitor, an antioxidant, and an intermediate in the synthesis of dyes, motor fuels, and oils; in photographic processing; and naturally in certain plant species, Hydroquinone is a phenol derivative with antioxidant properties that can cause toxicity in several organs, notably the kidney. 
Used as a topical treatment for skin hyperpigmentation and in various cosmetic products, it is metabolized mainly to glutathione conjugates and forms mutagenic DNA adducts in in-vitro systems.

Hydroquinone appears as light colored crystals or solutions. 
May irritate the skin, eyes and mucous membranes. 
Mildly toxic by ingestion or skin absorption.

Hydroquinone is a benzenediol comprising benzene core carrying two hydroxy substituents para to each other.
Hydroquinone has a role as a cofactor, a carcinogenic agent, an Escherichia coli metabolite, a human xenobiotic metabolite, a skin lightening agent, an antioxidant and a mouse metabolite. 
Hydroquinone is a benzenediol and a member of hydroquinones.

Use and Manufacturing of Hydroquinone
Hydroquinone is used as a developing agent in black-and-white photography, lithography, and x-ray films. 
Hydroquinone is also used as an intermediate to produce antioxidants for rubber and food. 
Hydroquinone is added to a number of industrial monomers to inhibit polymerization during shipping, storage, and processing.

Industry Uses of Hydroquinone
-Anti-Oxidant for Rubber Nabufacturing
-Inhibitor
-Intermediates
-Oxidizing/reducing agents
-Photosensitive chemicals
-Process regulators

Consumer Uses of Hydroquinone    
-Inhibitor
-Photographic supplies, film, and photo chemicals

Household Products of Hydroquinone        
Household & Commercial/Institutional Products
Information on 48 consumer products that contain Hydroquinone in the following categories is provided:
-Auto Products
-Inside the Home
-Personal Care

Methods of Manufacturing of Hydroquinone
p-Diisopropylbenzene (p-DIPB) is produced by Friedel-Crafts alkylation of benzene with propene. 
Purified p-DIPB is subsequently converted to the dihydroperoxide (DHP) by air oxidation under slightly alkaline conditions at 80 - 90 °C. 
The DHP is separated from the reaction mixture either by extraction or by crystallization, and is then cleaved to hydroquinone and acetone by an acid-catalyzed Hock rearrangement; the DHP solution is treated with sulfuric acid catalyst (0.2 - 1.0%) at 60 - 80 °C. 
The hydroquinone is crystallized and isolated. 
The overall yield of hydroquinone (based on p-DIPB) is ca. 80%.

The catalyzed hydroxylation of phenol at ca. 80 °C with 70% aqueous hydrogen peroxide produces a mixture of hydroquinone and catechol. 
The catalyst may be a strong mineral acid, iron(II), or a cobalt(II) salt. 
Depending on catalyst selection, the ratio of catechol to hydroquinone can be varied from 3:1 to 0.1:1; in practice, the ratio is typically 1.5:1, i.e., catechol is the major product. 

The reaction proceeds by an ionic mechanism in which hydrogen peroxide is polarized by the strong acid catalyst and phenol is subsequently hydroxylated the resulting isomers are separated by a series of extractions and solvent-stripping operations. 
The ratio of the products hydroquinone and catechol may be influenced by the presence of superacids or shape-selective zeolites. 
Thus, use of a vanadium-modified Nafion perfluorosulfonate polymer for the oxidation of phenol gave a hydroquinone-catechol ratio of 12.5:1. 
The use of a shape-selective zeolite in the hydroxylation of phenol has yielded hydroquinone with 99% selectivity.

Oxidation of aniline is the oldest process used for the production of hydroquinone. 
Aniline is oxidized with manganese dioxide (15-20% excess) in aqueous sulfuric acid at 0 - 5 °C to produce p-benzoquinone. 
This intermediate is removed from the reaction mixture by steam stripping and collected. 
A byproduct, manganese sulfate, may be retrieved from the depleted reaction mixture and sold for agricultural applications. 

Hydroquinone is obtained from the intermediate p-benzoquinone by reduction with iron at 55 - 65 °C or by catalytic hydrogenation. 
The product (usually technical grade) is crystallized, isolated from the typically aqueous stream by centrifugation, and dried in a vacuum dryer. 
The overall yield of hydroquinone from aniline is ca. 85%.
Prepared by oxidation of aniline;... by reduction of quinone; ... by Elbs persulfate oxidation of phenol; ... from acetylene + carbon monoxide.

General Manufacturing Information
Industry Processing Sectors
-All other basic organic chemical manufacturing
-Photographic film (typical silver halide film) processing chemistry
-Photographic film paper, plate, and chemical manufacturing
-Plastic material and resin manufacturing
-Rubber product manufacturing

Hydroquinone is used to lighten the dark patches of skin (also called hyperpigmentation, melasma, "liver spots," "age spots," freckles) caused by pregnancy, birth control pills, hormone medicine, or injury to the skin.This medicine works by blocking the process in the skin that leads to discoloration.
Hydroquinone is a skin-lightening agent. 
It bleaches the skin, which can be helpful when treating different forms of hyperpigmentation.

Historically, there’s been some back-and-forth on the safety of hydroquinone. 
In 1982, the U.S. Food and Drug Administration recognized the ingredient as safe and effectiveTrusted Source.
Several years later, concerns about safety prompted retailers to pull hydroquinone from the market. 
The FDA went on to discover that many of the products in question contained contaminants like mercury. 
They established that these contaminants were behind reports of adverse effects.

Hydroquinone is a skin-lightening agent used topically for the treatment of hyperpigmentation.
Hydroquinone should not be used by individuals allergic to hydroquinone or any of the excipients in the formulation such as the preservative metabisulphite. 
Hydroquinone is used in a cream or lotion formulation in a concentration of 1-5%. It is often found in a combination formulation with other skin lightening agents such as topical retinoids (to increase efficiency) and low potency topical steroids (to reduce irritancy).
In New Zealand and many other countries, hydroquinone is only available on prescription, and may need to be compounded by the pharmacist.
Hydroquinone must be distinguished from monobenzyl ether of hydroquinone which can cause irreversible pigment loss.

Hydroquinone is a topical skin-bleaching agent used in the cosmetic treatment of hyperpigmented skin conditions. 
The effect of skin lightening caused by hydroquinone is reversible when exposed to sunlight and therefore requires regular use until desired results are achieved. 
Various preparations are available including creams, emulsions, gels, lotions and solutions. 
It is available over the counter in a 2% cream and can be prescribed by your dermatologist in higher concentrations.

Mechanism: Hydroquinone produces reversible lightening of the skin by interfering with melanin production by the melanocytes. 
Specifically, inhibition of the enzymatic conversion of tyrosine to DOPA (dihydroxyphenylalanine) results in the desired chemical reduction of pigment. 
Ultimately, this causes a decrease in the number of melanocytes and decreased transfer of melanin leading to lighter skin.

Uses: Popularized by its usage as a photo-developer, hydroquinone can be used in any condition causing hyperpigmentation. 
Common conditions include melasma, freckles, lentigines, age spots and acne scars. 
Skin sensitivity to hydroquinone may be determined before treatment by applying a small amount of cream to the hyperpigmented area and noting any redness or itching. 
If no reaction occurs, initiate treatment. 
As a general rule, always ensure the area is clean and dry then apply a thin film to the lesion and rub it into the skin well. 
Hands should be washed after the application to avoid unwanted lightening of the fingers.

To maintain the desired affect, hydroquinone should be used concurrently with a strong sunscreen. 
Many preparations are available as a combination product. 
Lightening of the skin should be noticed within 4 weeks of initiation, if no change is seen in 3 months, contact your dermatologist for further recommendations.

Side Effects: Normally hydroquinone is very well tolerated, however side effects may be seen. 
These include dryness, irritation, pruritus, erythema, and a mild irritant contact dermatitis. 
Furthermore, remember to avoid contact with eyes and use sparingly on the face. 
Prolonged usage of hydroquinone has been associated with ochronosis, a blue-black pigmentation with caviar-like papules on the skin.

Hydroquinone (HQ), a phenolic compound, is also known as 1,4-dihydroxy-benzene. 
The detection of HQ along with resorcinol and phenol in air samples by synchronous fluorescence method has been proposed. 
The electrochemical oxidation of HQ has been studied using cyclic and differential pulse voltammetry. 
Hydroquinone (HQ)s enthalpies of sublimation, vaporization and fusion have been reported.
 
Hydroquinone may be used to synthesize bicyclic phosphonate derivative by reacting with phosphonic dichloride.
Hydroquinone is mainly used as a photographic developer.
Hydroquinone and its alkylate are widely used as polymerization inhibitors in monomer storage and transportation, and the concentration is usually about 200ppm.
Hydroquinone  is an intermediate of edible oil antioxidant BHA; hydroquinone is an intermediate of dyes, organic pigments and perfumes; hydroquinone is an intermediate of photosensitive pigments and dyes .

Hydroquinone is also used in the preparation of N, N’-diphenyl-p-phenylenediamine, which is an antioxidant and anti-odor agent for rubber and gasoline.
Photometric determination of phosphorus, magnesium, niobium, copper, silicon and arsenic. 
Polarographic and volumetric determination of iridium. 

Reducing agent of heteropoly acid, reducing agent of copper and gold.
In the field of water treatment, adding hydroquinone to the hot water and cooling water of the closed-circuit heating and cooling system can inhibit corrosion of the metal on the water side. 
Hydroquinone is used as a deoxidizer for boiler water, and hydroquinone is added to it when the boiler water is preheated and deoxygenated to remove residual dissolved oxygen.

Hydroquinone is frequently found in skin-lightening products like bleaching creams. 
Hydroquinone works by limiting your production of melanin, the hormone that darkens your skin. 
While some people use it to lighten their darker skin, hydroquinone creams are most commonly used to lighten small, dark patches like sunspots or hyperpigmentation.

Creams with hydroquinone as an ingredient are an excellent non-surgical aesthetic procedure to help you achieve the skin you have always wanted. 
Unlike skin lightening surgery, hydroquinone creams are a cosmetic procedure that can be undertaken in the comfort of your own home after the initial consultation with your dermatologist. 
If you have dark patches or old sunspots, creams with hydroquinone can lighten them and – when combined with other suitable skincare ingredients – can help your skin recover from sun damage.

Hydroquinone is used as a developing agent in photography and as an antioxidant in rubber and food.
Tinnitus (ringing in the ears), dizziness, headache, nausea, vomiting, dyspnea, erosion of the gastric mucosa, edema of internal organs, cyanosis, convulsions, delirium, and collapse may result from the ingestion of a large amount of hydroquinone in humans. 
Hydroquinone is also a skin irritant in humans.

Chronic (long-term) occupational exposure to hydroquinone dust can result in eye irritation, corneal effects, and impaired vision. 
No information is available on the reproductive, developmental, or carcinogenic effects of hydroquinone in humans. There was some evidence of carcinogenic activity in orally-exposed rodents. 
Increased skin tumor incidence has been reported in mice treated dermally. 
EPA has not classified hydroquinone for carcinogenicity.

Hydroquinone is used as a developing agent in black-and-white photography, lithography, and x-ray films. 
Hydroquinone is also used as an intermediate to produce antioxidants for rubber and food. It is added to a number of industrial monomers to inhibit polymerization during shipping, storage, and processing.

Hydroquinone is found in a variety of topical skin treatments, from face moisturizers to cleansers to skin-lightening creams. 
It’s often used in combination with other products to help improve the complexion and treat a condition called melasma.
Melasma is a common condition with the skin that results in discolored, dark spots, or patches. 
It’s more common in women than in men and most often occurs on the forehead, cheeks, chin, and bridge of the nose, though it can happen anywhere on the body.

Hydroquinone belongs to a combination of 'skin cosmetics' primarily used for brighter, more radiant skin complexation. 
Besides this, it is also used to clears the complexion and acne scars, hyperpigmentation, melasma, and photoaging (premature ageing of the skin caused by repeated exposure to UV radiation). 
Hyperpigmentation is a skin condition in which patches of skin become darker in colour than the normal surrounding skin. 
Melasma is a common skin problem that causes dark, discoloured patches on your skin. 
Dark spots occur when some skin areas start producing more melanin (a natural pigment that gives colour to eyes, hair and skin), ranging from light to dark brown.

Hydroquinone contains  (skin lightening or bleaching agent) which works by decreasing the amount of melanin (a skin pigment) that is responsible for the darkening of the skin. Hydroquinone is primarily used to treat melasma (dark brown patch on skin), hyperpigmentation.
Hydroquinone is an organic compound that’s used to treat a variety of discoloration-related skin conditions. 
It’s a skin lightening agent that works by reducing your production of melanin. 
When used topically, hydroquinone can cause your skin to lighten in color.

Hydroquinone is widely used as a scar treatment. 
Applied topically, it can cause darkened scars to lose some or all of their extra pigmentation, causing them to blend in and match the color of the surrounding skin.
It’s also used as a treatment for skin hyperpigmentation caused by UV exposure (spending too much time in the sun) and inflammation.
Topical hydroquinone creams are available as prescription medication to treat melasma and other pigmentation-related skin conditions. 

Hydroquinone is produced industrially in several countries. 
In 1979, the total world capacity for production exceeded 40 000 tonnes, while in 1992 it was approximately 35 000 tonnes. 
Hydroquinone is extensively used as a reducing agent, as a photographic developer, as an antioxidant for many oxidizable products, as a stabilizer or polymerizing inhibitor for certain materials that polymerize in the presence of free radicals, and as a chemical intermediate for the production of antioxidants, antiozonants, agro-chemicals, and polymers. 
It is a skin-lightening agent and is used in cosmetics, hair dyes, and medical preparations.

Hydroquinone is a chemical substance that acts as a skin-lightening agent. 
Hydroquinone can lighten the dark parts of the skin occurring due to hyperpigmentation or some kind of injury. 
Hydroquinone is a depigmentation agent for the skin as it reduces the formation of melanin. 
Melanin is the pigment that gives skin its unique brownish hue. 
Hydroquinone is available in cream, emulsion, gel, and lotion forms and can be purchased over the counter.

Hydroquinone is a skin-lightening agent that treats darker skin patches. The chemical is useful to treat dark skin that may occur due to:
-Melasma
-Chloasma
-Acne scars
-Lentigines or darkening due to sun exposure
-Freckles or dark patches on fair skin
-Post-inflammatory hyperpigmentation
-Pregnancy
-Intake of birth control pills
-Hormonal changes

Hydroquinone is an aromatic organic compound with the chemical formula C6H4(OH)2, also known as benzene-1,4-diol or quinol, which is a kind of phenol and also a derivative of benzene. 
Hydroquinone contains two hydroxyl groups bonded in a para position to the benzene ring. 
Hydroquinone is a granular white solid. 
This parent compound’s substituted derivatives are also known as hydroquinones. 
Friedrich Wöhler coined the term “hydroquinone” in 1843.

Hydroquinone has several applications, which are primarily associated with its function as a reducing agent that is soluble in water. 
Hydroquinone is a major component of most black and white photographers for film and paper where, with the compound metol, it transforms silver halides into elemental silver.

Properties of Hydroquinone
-Formula of hydroquinone is C6H6O2.
-The Molecular Weight is 110.11 g/mol.
-The Boiling Point of hydroquinone is 287°C
-Also, the Melting Point of hydroquinone is 172°C.
-The Density of hydroquinone is 1.3gcm−3.
-Hydroquinone is soluble in water.
-Hydroquinone has a white-solid appearance.

Uses of Hydroquinone
The uses of hydroquinone are:

-As a reducing agent.
-For the preventive measures of methyl methacrylate.
-In skin whitening.
-Helpful as a biomarker for benzene exposure.
-By photographic developers
-In the treatment of acne scars
-In various cosmetic products

Hydroquinone has several applications, which are primarily associated with its function as a reducing agent that is soluble in water. 
Hydroquinone is a major component of most black and white photographers for film and paper where, with the compound metol, it transforms silver halides into elemental silver.
There are several other applications for its reducing power. 
As a polymerization barrier, hydroquinone inhibits the polymerization of acrylic acid, methyl methacrylate, cyanoacrylate, and other monomers vulnerable to radical-initiated polymerization by using its antioxidant properties.
By serving as a free-radical scavenger, hydroquinone helps in improving the shelflife of light-sensitive resins such as preceramic polymers. 
Hydroquinone can form a diphenolate ion by losing a hydrogen cation from both hydroxyl groups.

Hydroquinone is used as an inhibitor of polymerization. 
Due to its outstanding photo developing properties, it is also used as a photo developer, and as a raw material in manufacturing dye intermediates.
Hydroquinone is a drug used to treat increased pigmentation of the skin (hyperpigmentation). 
Hyperpigmentation causes irregular brown spots on the skin, often on the face.

Precautionary Statements of Hydroquinone
Prevention
Obtain special instructions before use
Do not handle until all safety precautions have been read and understood
Use personal protective equipment as required
Wash face, hands and any exposed skin thoroughly after handling
Do not eat, drink or smoke when using this product
Avoid breathing dust/fume/gas/mist/vapors/spray
Contaminated work clothing should not be allowed out of the workplace
Wear protective gloves
Use only outdoors or in a well-ventilated area

Inhalation
IF INHALED: 
Remove victim to fresh air and keep at rest in a position comfortable for breathing.

Skin
IF ON SKIN: Wash with plenty of soap and water
If skin irritation or rash occurs: Get medical advice/attention
Wash contaminated clothing before reuse.

Eyes
IF IN EYES: 
Rinse cautiously with water for several minutes. 
Remove contact lenses, if present and easy to do. 
Continue rinsing Immediately call a POISON CENTER or doctor/physician.

Ingestion
IF SWALLOWED: Call a POISON CENTER or doctor/physician if you feel unwell
Rinse mouth.


Substance identity

EC / List no.: 204-617-8
CAS no.: 123-31-9
Mol. formula: C6H6O2

Hazard classification & labelling of Hydroquinone
Danger! According to the harmonised classification and labelling (ATP01) approved by the European Union, this substance is very toxic to aquatic life, is harmful if swallowed, causes serious eye damage, is suspected of causing genetic defects, is suspected of causing cancer and may cause an allergic skin reaction.
Additionally, the classification provided by companies to ECHA in REACH registrations identifies that this substance is very toxic to aquatic life with long lasting effects.

About Hydroquinone
Hydroquinonee is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, at ≥ 10 000 to < 100 000 tonnes per annum.
Hydroquinone is used by consumers, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Consumer Uses of Hydroquinone
Hydroquinone is used in the following products: photo-chemicals.
Other release to the environment of Hydroquinone is likely to occur from: indoor use as reactive substance.

Article service life of Hydroquinone
ECHA has no public registered data on the routes by which this substance is most likely to be released to the environment. ECHA has no public registered data indicating whether or into which articles the substance might have been processed.

Widespread uses by professional workers of Hydroquinone
Hydroquinone is used in the following products: photo-chemicals, coating products, inks and toners and polymers. This substance is used in the following areas: printing and recorded media reproduction, health services and scientific research and development. Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners).

Formulation or re-packing of Hydroquinone
Hydroquinone is used in the following products: photo-chemicals, water treatment chemicals and fuels.
Release to the environment of Hydroquinone can occur from industrial use: formulation of mixtures and formulation in materials.

Uses at industrial sites of Hydroquinone
Hydroquinone is used in the following products: photo-chemicals, polymers, coating products, inks and toners and water treatment chemicals.
Hydroquinone has an industrial use resulting in manufacture of another substance (use of intermediates).
Hydroquinone is used in the following areas: printing and recorded media reproduction and formulation of mixtures and/or re-packaging.
Hydroquinone is used for the manufacture of: chemicals and plastic products.
Release to the environment of Hydroquinone can occur from industrial use: as processing aid, as an intermediate step in further manufacturing of another substance (use of intermediates) and for thermoplastic manufacture.

Manufacture of Hydroquinone
Release to the environment of Hydroquinone can occur from industrial use: manufacturing of the substance.

Synonyms:
hydroquinone
Benzene-1,4-diol
1,4-benzenediol
123-31-9
Quinol
1,4-Dihydroxybenzene
p-Benzenediol
p-Hydroquinone
p-Hydroxyphenol
4-Hydroxyphenol
p-Dihydroxybenzene
Benzoquinol
Eldoquin
hydroquinol
Eldopaque
Phiaquin
p-Dioxybenzene
Dihydroquinone
Hydroquinole
Idrochinone
Tecquinol
Solaquin forte
Benzohydroquinone
Arctuvin
Hidroquinone
Tequinol
Dihydroxybenzene
Derma-Blanch
Tenox HQ
Hydrochinon
Hydrochinone
Artra
Eldopaque Forte
Eldoquin Forte
Diak 5
Benzene, p-dihydroxy-
1,4-Dihydroxy-benzol
Usaf ek-356
1,4-Diidrobenzene
p-Dioxobenzene
1,4-Dihydroxybenzen
para-Dioxybenzene
para-Hydroquinone
Pyrogentistic acid
1,4-Dihydroxy-benzeen
NCI-C55834
HE 5
para-Dihydroxybenzene
Black and White Bleaching Cream
Melanex
Idrochinone [Italian]
Hydrochinon [Czech, Polish]
1,4-Dihydroxybenzen [Czech]
1,4-Diidrobenzene [Italian]
1,4-Dihydroxy-benzeen [Dutch]
1,4-Dihydroxy-benzol [German]
UNII-XV74C1N1AE
NSC 9247
UN2662
Hydroquinone [USP]
CHEBI:17594
AI3-00072
4-DIHYDROXYBENZENE
MFCD00002339
HQ
CHEMBL537
XV74C1N1AE
1,4-Benzenediol, homopolymer
DTXSID7020716
NSC-9247
Hydroquinone [UN2662] [Poison]
Hydroquinone (USP)
NCGC00015523-02
beta-quinol
DSSTox_CID_716
para-Hydroxyphenol
DSSTox_RID_75754
DSSTox_GSID_20716
Eldopacque
Hydroquinone (Benzene-1,4-diol)
Epiquin
Sunvanish
p Benzendiol
p-Dihydroquinone
alpha-hydroquinone
26982-52-5
CAS-123-31-9
SMR000059154
CCRIS 714
1,4-Hydroxybenzene
HSDB 577
SR-01000075920
EINECS 204-617-8
hydroquinon
Hydroquinoue
hydroq uinone
hydroquinone gr
a-Hydroquinone
Black & White Bleaching Cream
p-Hydroxybenzene
b-Quinol
4-Benzenediol
Hydroquinone, HQ
.beta.-Quinol
1,4 benzenediol
Hydroquinone,(S)
p-dihydroxy benzene
HQE
Hydroquinone polymer
PLQ
Artra (Salt/Mix)
1, 4-Benzenediol
HYDROP
.alpha.-Hydroquinone
phenol derivative, 4
4-hydroxyphenyl alcohol
Spectrum_001757
4e3h
SpecPlus_000769
1,4-Dihydrobenzoquinone
ELDOQUIN (TN)
hydroquinone for synthesis
Spectrum2_001672
Spectrum3_000656
Spectrum4_000633
Spectrum5_001430
Lopac-H-9003
1,2 BENZOLDIOL
WLN: QR DQ
bmse000293
Epitope ID:116206
EC 204-617-8
Lopac0_000577
SCHEMBL15516
BSPBio_002291
KBioGR_001246
KBioSS_002237
1,4-Dihydroxybenzene, XIII
MLS000069815
MLS001074911
BIDD:ER0340
DivK1c_006865
Hydroquinone, LR, >=99%
SPECTRUM1504237
Hydrochinon(CZECH, POLISH)
SPBio_001883
BDBM26190
Hydroquinone, puriss., 99.0%
KBio1_001809
KBio2_002237
KBio2_004805
KBio2_007373
KBio3_001511
NSC9247
Benzene-1,4-diol (Hydroquinone)
HMS1922H15
HMS2093E08
HMS3261D16
LABOTEST-BB LTBB001931
Pharmakon1600-01504237
HY-B0951
ZINC5133378
Tox21_110169
Tox21_202345
Tox21_300015
Tox21_500577
CCG-39082
NSC758707
s4580
STK397446
AKOS000119003
Tox21_110169_1
AM10548
AS00174
DB09526
LP00577
MCULE-3953269041
NSC-758707
SDCCGSBI-0050559.P003
UN 2662
Hydroquinone, ReagentPlus(R), >=99%
Hydroquinone, USP, 99.0-100.5%
NCGC00015523-01
NCGC00015523-03
NCGC00015523-04
NCGC00015523-05
NCGC00015523-06
NCGC00015523-07
NCGC00015523-08
NCGC00015523-09
NCGC00015523-10
NCGC00015523-11
NCGC00015523-12
NCGC00015523-13
NCGC00015523-19
NCGC00090880-01
NCGC00090880-02
NCGC00090880-03
NCGC00090880-04
NCGC00090880-05
NCGC00254037-01
NCGC00259894-01
NCGC00261262-01
BP-21160
DA-33570
Hydroquinone, ReagentPlus(R), >=99.5%
SBI-0050559.P002
Hydroquinone, SAJ first grade, >=99.0%
EU-0100577
FT-0606877
H0186
Hydroquinone, SAJ special grade, >=99.0%
Hydroquinone, meets USP testing specifications
C00530
D00073
H 9003
AB00053361_08
Quinol; 1,4-Benzenediol; 1,4-Dihydroxybenzene
Q419164
J-004910
J-521469
SR-01000075920-1
SR-01000075920-4
Q27102742
Z57127551
094CADDB-59BF-4EDF-B278-59791B203EA2
F1908-0167
Hydroquinone, certified reference material, TraceCERT(R)
Hydroquinone, United States Pharmacopeia (USP) Reference Standard
Hydroquinone, Pharmaceutical Secondary Standard; Certified Reference Material
1,4-Dihydroxybenzene
1,4-dihydroxybenzene
1,4-dihydroxybenzene; hydroquinone; quinol
Hydroquinone
hydroquinone
quinol
Hydroquinone
1,4- benzodiol (cs)
1,4-dihidroksibenzen (hr)
1,4-dihidroksibenzen (sl)
1,4-dihidroksibenzenas (lt)
1,4-dihidroksibenzols (lv)
1,4-dihidroxibenceno (es)
1,4-dihidroxibenzen (mt)
1,4-dihidroxibenzen (ro)
1,4-dihidroxibenzeno (pt)
1,4-dihidroxibenzol (hu)
1,4-Dihydroksibentseeni (fi)
1,4-dihydroksybenzen (no)
1,4-dihydroksybenzen (pl)
1,4-dihydroxibensen (sv)
1,4-dihydroxybenzeen (nl)
1,4-dihydroxybenzen (da)
1,4-Dihydroxybenzol (de)
1,4-dihydroxybenzène; hydroquinone; quinol (fr)
1,4-dihüdroksübenseen (et)
1,4-diidrossibenzene (it)
1,4-διυδροξυ-βενζόλιο (el)
1,4-дихидрооксибензен (bg)
benzén-1,4-diol (sk)
chinol (cs)
Chinol (de)
chinol (mt)
chinol (nl)
chinol (ro)
chinol (sk)
chinolis (lt)
chinolo (it)
hidrochinonas (lt)
hidrochinonă (mt)
hidrochinonă (ro)
hidrohinons (lv)
hidrokinon (hr)
hidrokinon (hu)
hidrokinon (sl)
hidroquinona (es)
hidroquinona (pt)
hinols (lv)
hydrochinon (cs)
Hydrochinon (de)
hydrochinon (nl)
hydrochinon (pl)
hydrochinón (sk)
hydrokinon (no)
hydrokinon (sv)
hydrokinoni (fi)
hydroquinon (da)
hydroquinone (fr)
hüdrokinoon (et)
idrochinone (it)
kinol (hr)
kinol (hu)
kinol (sl)
kinol (sv)
kinoli (fi)
kinool (et)
quinol (da)
quinol (es)
quinol (fr)
quinol (pt)
κινόλη (el)
υδροκινόνη (el)
хидрохинон (bg)
хинол (bg)
1,4-Benzenediol
1,4-Benzenediol
1,4-Benzenediol, 1,4-Dihydroxybenzene, HQ, Quinol
1,4-Benzodiol
1,4-DIHYDROXYBENZENE
1,4-Dihydroxybenzene
1,4-dihydroxybenzene
1,4-dihydroxybenzene; hydroquinone; quinol
1,4-dyhydroxybenzene; hydroquinone, quinol
benzene, 1,4-dihydroxy
Benzene-1,4-diol
benzene-1,4-diol
Benzene-4,1-diol
hydoquinone
Hydrochinon
HYDROQUINONE
Hydroquinone
hydroquinone
Hydroquinone
hydroquinone
hydroquinone
quinol
Hydroquinone
Hydroquinone IG
Hydroquinone Photo
Hydroquinone Technical
Idrochinone
Idrochinone IG
Idrochinone Photo
Idrochinone tecnico
123-31-9
604-005-00-4
8027-02-9
8027-02-9
57534-13-1
57534-13-1


 

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