1,4-HYDROXY BENZENE (HYDROQUINONE)

1,4-Hydroxy benzene (hydroquinone) is an aromatic organic compound that is a type of phenol, a derivative of benzene.
1,4-Hydroxy benzene (hydroquinone) is extensively applied in the photographic industry as a key developer component due to its ability to reduce silver halides to metallic silver.
1,4-Hydroxy benzene (hydroquinone) is widely recognized for its strong reducing properties and its ability to act as an antioxidant, which makes it valuable in various industrial and pharmaceutical applications.

CAS Number: 123-31-9
EC Number: 204-617-8
Molecular Formula: C6H6O2
Molecular Weight: 110.11 g/mol

Synonyms: 1,4-Benzenediol, 1,4-Benzoquinol, 1,4-benzosemiquinone, 1,4-Dihydroxy-benzeen, 1,4-Dihydroxy-benzol, 1,4-Dihydroxybenzen, 1,4-Dihydroxybenzen, 1,4-dihydroxybenzene, 1,4-Diidrobenzene, 123-31-9, 204-617-8, 3225-30-7, 4-hydroxyphenol, 4-Hydroxyphenoxy, 605970, AIDA, Benzene, p-dihydroxy-, benzene-1,4-diol, Benzol-1,4-diol, BQ(H), dihydroquinone, Hydrochinon, hydroquinol, Hydroquinone, Hydroquinone, p-benzenediol, p-Dihydroquinone, p-Dihydroxybenzene, p-hydroquinone, p-Phenylenediol, p-Quinol, para-Dihydroxybenzene, quinol, 1,4-Benzendil, 1,4-Benzene-2,3,5,6-d4-diol-d2, 1,4-Benzoquinone, 1,4-Dihydrobenzoquinone, 1,4-Dihydroxy-benzeen, 1,4-Dihydroxy-benzol, 1,4-dihydroxybenzene (ring-d4), 1,4-Dihydroxybenzene, Quinol, 1,4-Diidrobenzene, 1,4-Hydroxybenzene, 1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl, 4-hydroxyphenyloxyl, 71589-26-9, 95041-90-0, 99%, a-Hydroquinone, ARCTUVIN, Artra, b-Quinol, Benzohydroquinone, Benzoquinol, Benzosemiquinone, Black and White Bleaching Cream, CAH12_HUMAN, CAH13_MOUSE, CAH14_HUMAN, CAH1_HUMAN, CAH2_HUMAN, CAH3_HUMAN, CAH4_HUMAN, CAH5A_HUMAN, CAH5B_HUMAN, CAH6_HUMAN, CAH7_HUMAN, CAH9_HUMAN, Carbonic anhydrase 1, Carbonic anhydrase 12, Carbonic anhydrase 13, Carbonic anhydrase 14, Carbonic anhydrase 2, Carbonic anhydrase 3, Carbonic anhydrase 4, Carbonic anhydrase 5A, mitochondrial, Carbonic anhydrase 5B, mitochondrial, Carbonic anhydrase 6, Carbonic anhydrase 7, Carbonic anhydrase 9, Derma-Blanch, Dihydroxybenzene, Eldopacque, Eldopaque, Eldoquin, Elopaque, Esoterica, Hidroquilaude, Hidroquin, Hidroquinona Isdin, Hidroquinone, HQE, Hydrochinon, Hydrochinone, hydrokinone., HYDROP, Hydroquinole, Hydroquinone for synthesis, Hydroquinone gr, Hydroquinone-d4, Hydroquinoue, Idrochinone, Idrochinone, Licostrata, Lustra, Melanasa, Melanex, Melpaque, Melquin, Neostrata HQ, p-Benzosemiquinone, p-benzosemiquinone radical, p-Dioxobenzene, p-Dioxybenzene, p-Diphenol, p-Hydroxybenzene, p-Hydroxyphenol, P4HA1_CHICK, para-Dioxybenzene, para-Hydroquinone, para-Hydroxyphenol, Phenoxy, 4-hydroxy-, Phiaquin, PLQ, Polyphenol oxidase 2, PPO2_AGABI, Prolyl 4-hydroxylase subunit α-1, Pyrogentistic acid, QR DQ, quinnone, Quinol;1,4-Benzenediol;1,4-Dihydroxybenzene;HQ, semiquinone radical, Solaquin, Solaquin Forte, Tecquinol, Tenox HQ, Tequinol, TYRO_HUMAN, TYRO_MOUSE, Tyrosinase, Ultraquin, α-Hydroquinone, β-Quinol, 对苯二酚

1,4-Hydroxy benzene (hydroquinone) is an aromatic organic compound characterized by a benzene ring substituted with two hydroxyl groups in the para (1,4-) position, giving it the chemical formula C₆H₄(OH)₂.
1,4-Hydroxy benzene (hydroquinone) appears as white to off-white crystalline solids and is highly soluble in water, alcohol, and ether.

1,4-Hydroxy benzene (hydroquinone) is widely recognized for its strong reducing properties and its ability to act as an antioxidant, which makes it valuable in various industrial and pharmaceutical applications.
1,4-Hydroxy benzene (hydroquinone) is sensitive to air and light and can gradually oxidize to form quinones, leading to discoloration.

1,4-Hydroxy benzene (hydroquinone) is extensively used in photographic development, polymerization inhibitors, cosmetics (especially skin-lightening formulations), and as an intermediate in chemical synthesis due to its reactivity and stability under controlled conditions.
1,4-Hydroxy benzene (hydroquinone) is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2.

1,4-Hydroxy benzene (hydroquinone) has two hydroxyl groups bonded to a benzene ring in a para position.
1,4-Hydroxy benzene (hydroquinone) is a white granular solid.

Substituted derivatives of this parent compound are also referred to as 1,4-Hydroxy benzene (hydroquinone)s.
The name "1,4-Hydroxy benzene (hydroquinone)" was coined by Friedrich Wöhler in 1843.

In 2023, 1,4-Hydroxy benzene (hydroquinone) was the 274th most commonly prescribed medication in the United States, with more than 800,000 prescriptions.

1,4-Hydroxy benzene (hydroquinone) is an aromatic organic compound which is a type of phenol, having the chemical formula C6H4(OH)2.
1,4-Hydroxy benzene (hydroquinone)'s chemical structure has two hydroxyl groups bonded to a benzene ring in a para position.

1,4-Hydroxy benzene (hydroquinone) is commonly used as a biomarker for benzene exposure.
The presence of 1,4-Hydroxy benzene (hydroquinone) in normal individuals stems mainly from direct dietary ingestion, catabolism of tyrosine and other substrates by gut bacteria, ingestion of arbutin-containing foods, cigarette smoking, and the use of some over-the-counter medicines.

1,4-Hydroxy benzene (hydroquinone) is a white granular solid at room temperature and pressure.
The hydroxyl groups of 1,4-Hydroxy benzene (hydroquinone) are quite weakly acidic.

1,4-Hydroxy benzene (hydroquinone) can lose an H+ from one of the hydroxyls to form a monophenolate ion or lose an H+ from both to form a diphenolate ion.
1,4-Hydroxy benzene (hydroquinone) has a variety of uses principally associated with its action as a reducing agent which is soluble in water.
1,4-Hydroxy benzene (hydroquinone) is a major component of most photographic developers where, with the compound Metol, it reduces silver halides to elemental silver.

Uses of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-Hydroxy benzene (hydroquinone) is widely used as a reducing agent and antioxidant across multiple industrial applications.
1,4-Hydroxy benzene (hydroquinone) is extensively applied in the photographic industry as a key developer component due to its ability to reduce silver halides to metallic silver.

1,4-Hydroxy benzene (hydroquinone) is also used as a polymerization inhibitor in the production and storage of monomers such as styrene and acrylics, preventing unwanted premature reactions.
In the cosmetics industry, 1,4-Hydroxy benzene (hydroquinone) is utilized in skin-lightening and hyperpigmentation treatment products by inhibiting melanin synthesis.

1,4-Hydroxy benzene (hydroquinone) is further employed as an intermediate in the synthesis of dyes, pharmaceuticals, and agrochemicals.
Additionally, 1,4-Hydroxy benzene (hydroquinone) is used in rubber processing, coatings, adhesives, and as a stabilizer in various chemical formulations where oxidation control is critical.

1,4-Hydroxy benzene (hydroquinone) has a variety of uses principally associated with its action as a reducing agent that is soluble in water.
1,4-Hydroxy benzene (hydroquinone) 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 1,4-Hydroxy benzene (hydroquinone)'s reducing power.
As a polymerisation inhibitor, exploiting its antioxidant properties, 1,4-Hydroxy benzene (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, 1,4-Hydroxy benzene (hydroquinone) serves to prolong the shelf life of light-sensitive resins such as preceramic polymers.

1,4-Hydroxy benzene (hydroquinone) can lose a hydrogen cation from both hydroxyl groups to form a diphenolate ion.
The disodium diphenolate salt of 1,4-Hydroxy benzene (hydroquinone) is used as an alternating comonomer unit in the production of the polymer PEEK.

Skin depigmentation:
1,4-Hydroxy benzene (hydroquinone) is used as a topical application in skin whitening to reduce the color of skin.
1,4-Hydroxy benzene (hydroquinone) 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, United States Food and Drug Administration revoked its previous approval of 1,4-Hydroxy benzene (hydroquinone) and proposed a ban on all over-the-counter preparations.
The FDA officially banned 1,4-Hydroxy benzene (hydroquinone) in 2020 as part of a larger reform of the over-the-counter drug review process.

The FDA stated that 1,4-Hydroxy benzene (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 1,4-Hydroxy benzene (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 1,4-Hydroxy benzene (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 1,4-Hydroxy benzene (hydroquinone).
NTP evaluation showed some evidence of long-term carcinogenic and genotoxic effects.

While 1,4-Hydroxy benzene (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 proved 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.

In the anthraquinone process substituted 1,4-Hydroxy benzene (hydroquinone)s, typically anthra1,4-Hydroxy benzene (hydroquinone) are used to produce hydrogen peroxide which forms spontaneously on reaction with oxygen.
The type of substituted 1,4-Hydroxy benzene (hydroquinone) is selected depending on reactivity and recyclability.

Advantages of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-Hydroxy benzene (hydroquinone) provides strong reducing capability, allowing efficient control of oxidation reactions in various chemical and industrial systems.
1,4-Hydroxy benzene (hydroquinone) exhibits effective antioxidant behavior, helping to extend shelf life and maintain stability of formulations sensitive to oxygen.

1,4-Hydroxy benzene (hydroquinone) acts as a highly efficient polymerization inhibitor, even at low concentrations, reducing unwanted side reactions during storage and processing of monomers.
1,4-Hydroxy benzene (hydroquinone) demonstrates good solubility in water and organic solvents, enabling easy incorporation into different formulations.

1,4-Hydroxy benzene (hydroquinone) offers high reactivity with controlled stability under proper storage conditions, making it versatile for synthesis and industrial applications.
1,4-Hydroxy benzene (hydroquinone) contributes to consistent and reliable performance in photographic, cosmetic, and polymer industries due to its well-defined chemical behavior.

Natural Occurrences of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-Hydroxy benzene (hydroquinone)s 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 1,4-Hydroxy benzene (hydroquinone)s 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.

1,4-Hydroxy benzene (hydroquinone) is thought to be the active toxin in Agaricus hondensis mushrooms.
1,4-Hydroxy benzene (hydroquinone) has been shown to be one of the chemical constituents of the natural product propolis.

1,4-Hydroxy benzene (hydroquinone) is also one of the chemical compounds found in castoreum.
1,4-Hydroxy benzene (hydroquinone) is gathered from the beaver's castor sacs.

Production of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-Hydroxy benzene (hydroquinone) is produced industrially in two main ways.

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.
1,4-Hydroxy benzene (hydroquinone) reacts with air to afford the bis(hydroperoxide), which is structurally similar to cumene hydroperoxide and rearranges in acid to give acetone and 1,4-Hydroxy benzene (hydroquinone).
A second route involves hydroxylation of phenol over a catalyst.

The conversion uses hydrogen peroxide and affords a mixture of 1,4-Hydroxy benzene (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 1,4-Hydroxy benzene (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.
1,4-Hydroxy benzene (hydroquinone) and its derivatives can also be prepared by oxidation of various phenols, such as aniline and DIPB.

Examples include Elbs persulfate oxidation and Dakin oxidation.
1,4-Hydroxy benzene (hydroquinone) was first obtained in 1820 by the French chemists Pelletier and Caventou via the dry distillation of quinic acid.

Hydrolysis of chlorophenol.
The latter three methods are generally less atom-economical than oxidation with hydrogen peroxide, and their commercial practice in China produced serious pollution in 2022.

Reactions of 1,4-Hydroxy Benzene (Hydroquinone):
The reactivity of 1,4-Hydroxy benzene (hydroquinone)'s hydroxyl groups resembles that of other phenols, being weakly acidic.
The resulting conjugate base easily undergoes O-alkylation to give mono- and diethers.

Similarly, 1,4-Hydroxy benzene (hydroquinone) is highly susceptible to ring substitution via Friedel–Crafts alkylation.
This reaction is often used for the production of several popular antioxidants, namely 2-tert-butyl-4-methoxyphenol (BHA).
The useful dye quinizarin is produced by diacylation of 1,4-Hydroxy benzene (hydroquinone) with phthalic anhydride.

Redox:
1,4-Hydroxy benzene (hydroquinone) can be reversibly oxidised under mild conditions to give benzoquinone.
Naturally occurring 1,4-Hydroxy benzene (hydroquinone) derivatives, such as coenzyme Q, exhibit similar reactivity, wherein one hydroxyl group is exchanged for an amino group.
Given the conditional reversibility and relative ubiquity of reagents, oxidation reactions of 1,4-Hydroxy benzene (hydroquinone)s and 1,4-Hydroxy benzene (hydroquinone) derivatives are of significant commercial use, often used at an industrial scale.

When colorless 1,4-Hydroxy benzene (hydroquinone) and benzoquinone - bright yellow in solid form - are cocrystallized at a 1:1 ratio, a dark-green crystalline charge-transfer complex (melting point 171 °C), known as quinhydrone (C6H6O2·C6H4O2), is formed.
This complex dissolves in hot water, dissociating both quinone molecules in solution.

Amination:
An important reaction involves the conversion of 1,4-Hydroxy benzene (hydroquinone) to its mono- and di-amine derivatives.

One such derivative, methylaminophenol, used in photography, is produced according to the stochiometry:
C6H4(OH)2 + CH3NH2 → HOC6H4NHCH3 + H2O

Diamines - used in the rubber industry as antiozone agents - aminated from aniline, are formed via a similar pathway:
C6H4(OH)2 + 2 C6H5NH2 → C6H4(N(H)C6H5)2 + 2 H2O

Discovery of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-Hydroxy benzene (hydroquinone) is an aromatic organic compound that has garnered significant attention for its diverse applications in various fields, including photography, cosmetics, and medicine.
Discovered in the mid-19th century, 1,4-Hydroxy benzene (hydroquinone) is characterized by its two hydroxyl groups attached to a benzene ring.
1,4-Hydroxy benzene (hydroquinone)'s ability to act as a reducing agent makes it a valuable chemical in both industrial and laboratory settings.

The synthesis of 1,4-Hydroxy benzene (hydroquinone) can be achieved through several methods, including the reduction of quinone or the oxidation of catechol.
1,4-Hydroxy benzene (hydroquinone) exists as a white crystalline solid at room temperature and is soluble in water, alcohol, and ether.

1,4-Hydroxy benzene (hydroquinone) has been widely used in photography, particularly in the development of black-and-white films and prints.
1,4-Hydroxy benzene (hydroquinone)'s reducing properties allow it to convert exposed silver halides into metallic silver, thereby forming the image on the photographic medium.
Despite the advent of digital photography, 1,4-Hydroxy benzene (hydroquinone) remains a crucial component in traditional photographic processes and is valued for its effectiveness and reliability.

In the cosmetics industry, 1,4-Hydroxy benzene (hydroquinone) is renowned for its skin-lightening properties.
1,4-Hydroxy benzene (hydroquinone) is commonly used to treat hyperpigmentation, melasma, and age spots by inhibiting the enzyme tyrosinase, which is involved in the production of melanin.

By reducing melanin production, 1,4-Hydroxy benzene (hydroquinone) can effectively lighten dark areas of the skin.
1,4-Hydroxy benzene (hydroquinone)'s popularity in skin care products, particularly in formulations aimed at evening out skin tone and reducing discoloration, has led to its widespread use in creams, lotions, and serums.

Despite its effectiveness, the use of 1,4-Hydroxy benzene (hydroquinone) in cosmetics has raised concerns regarding safety and potential side effects.
Prolonged use can lead to a condition known as ochronosis, which results in a bluish-black discoloration of the skin.

Additionally, there are concerns about the potential carcinogenicity of 1,4-Hydroxy benzene (hydroquinone) when applied to the skin over extended periods.
As a result, several countries have implemented regulations regarding the concentration of 1,4-Hydroxy benzene (hydroquinone) in cosmetic products, with some banning its use altogether.
In the United States, for instance, over-the-counter products containing 1,4-Hydroxy benzene (hydroquinone) are limited to a maximum concentration of 2%, while higher concentrations are available only by prescription.

Beyond its applications in photography and cosmetics, 1,4-Hydroxy benzene (hydroquinone) also serves as a crucial intermediate in the synthesis of various chemical compounds.
1,4-Hydroxy benzene (hydroquinone) is utilized in the production of antioxidants, dyes, and resins, as well as in the manufacture of certain pharmaceuticals.
1,4-Hydroxy benzene (hydroquinone)'s reducing properties make it valuable in organic synthesis, where it is employed in redox reactions and as a reagent in various chemical transformations.

Research into the safety and efficacy of 1,4-Hydroxy benzene (hydroquinone) continues to evolve, with ongoing studies aimed at understanding its long-term effects and potential alternatives for skin lightening.
Natural alternatives, such as licorice extract and kojic acid, are being explored as safer options for individuals seeking to address hyperpigmentation without the risks associated with 1,4-Hydroxy benzene (hydroquinone).

1,4-Hydroxy benzene (hydroquinone)'s discovery and subsequent applications in photography, cosmetics, and chemical synthesis highlight its versatility and importance in various fields.
While 1,4-Hydroxy benzene (hydroquinone) remains a key player in many industrial processes, the growing awareness of safety concerns has prompted a shift towards exploring alternative solutions that ensure efficacy while minimizing health risks.
As research advances, the legacy of 1,4-Hydroxy benzene (hydroquinone) will undoubtedly influence future developments in both cosmetic science and organic chemistry.

Stability and Reactivity of 1,4-Hydroxy Benzene (Hydroquinone):

Chemical stability:
Stable under normal, dry storage conditions.

Reactivity:
Strong reducing agent.
Reacts with oxidizing agents.

Reacts with acids.
Reacts with moisture.

Conditions to avoid:
Heat.
Humidity.
Moisture.
Acidic conditions.

Incompatible materials:
Strong oxidizers.
Strong acids.
Nitrates.

Hazardous decomposition products:
Sulfur dioxide (SO₂) may be released.
Sulfur oxides may form.
Sodium oxides may be generated.

Handling and Storage of 1,4-Hydroxy Benzene (Hydroquinone):

Handling:
Avoid inhalation of dust.
Avoid contact with eyes and skin.
Use adequate ventilation.

Storage:
Store in a cool, dry, and well-ventilated place.
Keep container tightly closed.
Protect from moisture.

First Aid Measures of 1,4-Hydroxy Benzene (Hydroquinone):

Inhalation:
Move to fresh air.
Seek medical attention if symptoms persist.

Skin contact:
Wash with soap and water.

Eye contact:
Rinse cautiously with water for several minutes.
Seek medical attention if irritation continues.

Ingestion:
Rinse mouth.
Do not induce vomiting.
Seek medical advice immediately.

Firefighting Measures of 1,4-Hydroxy Benzene (Hydroquinone):

Suitable extinguishing media:
Use media appropriate for the surrounding fire.

Hazards:
Not highly flammable.
May release toxic sulfur dioxide fumes when heated.

Protective equipment:
Use self-contained breathing apparatus.
Wear protective clothing.

Accidental Release Measures of 1,4-Hydroxy Benzene (Hydroquinone):

Personal precautions:
Avoid dust formation.
Avoid inhalation.
Use appropriate personal protective equipment.

Environmental precautions:
Prevent entry into drains and waterways.

Methods for cleaning up:
Sweep up carefully.
Place in suitable containers.
Avoid generating dust.

Exposure Controls / Personal Protection of 1,4-Hydroxy Benzene (Hydroquinone):

Engineering controls:
Provide adequate ventilation.

Respiratory protection:
Use dust mask or respirator if needed.

Hand protection:
Wear chemical-resistant gloves.

Eye protection:
Use safety goggles.

Skin protection:
Wear protective clothing.

Identifiers of 1,4-Hydroxy Benzene (Hydroquinone):
CAS Number: 123-31-9
EC Number: 204-617-8
IUPAC Name: Benzene-1,4-diol
Molecular Formula: C₆H₆O₂
Molecular Weight: 110.11 g/mol
InChI: InChI=1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
InChIKey: QIGBRXMKCJKVMJ-UHFFFAOYSA-N
SMILES: C1=CC(=CC=C1O)O
PubChem CID: 785
ChemSpider ID: 757

Chemical Formula: C6H6O2
Average Molecular Weight: 110.1106
Monoisotopic Molecular Weight: 110.036779436
IUPAC Name: benzene-1,4-diol
Traditional Name: α-1,4-Hydroxy benzene (hydroquinone)
CAS Registry Number: 123-31-9
SMILES: 
OC1=CC=C(O)C=C1
InChI Identifier: 
InChI=1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
InChI Key: QIGBRXMKCJKVMJ-UHFFFAOYSA-N

Linear Formula: C6H4-1,4-(OH)2
CAS Number: 123-31-9
Molecular Weight: 110.11

Molecular formula: C6H6O2
Average mass: 110.112
Monoisotopic mass: 110.036779
ChemSpider ID: 764

CAS Number: 123-31-9
Beilstein Reference: 605970
ChEBI: CHEBI:17594
ChEMBL: ChEMBL537
ChemSpider: 764
DrugBank: DB09526
ECHA InfoCard: 100.004.199
EC Number: 204-617-8
Gmelin Reference: 2742
KEGG: D00073
PubChem CID: 785
RTECS number: MX3500000
UNII: XV74C1N1AE
UN number: 3077, 2662
CompTox Dashboard (EPA): DTXSID7020716
InChI: InChI=1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
Key: QIGBRXMKCJKVMJ-UHFFFAOYSA-N check
InChI=1/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
Key: QIGBRXMKCJKVMJ-UHFFFAOYAX
SMILES: c1cc(ccc1O)O

Properties of 1,4-Hydroxy Benzene (Hydroquinone):
Chemical formula: C6H6O2
Molar mass: 110.112 g·mol−1
Appearance: White solid
Density: 1.3 g cm−3, solid
Melting point: 172 °C (342 °F; 445 K)
Boiling point: 287 °C (549 °F; 560 K)
Solubility in water: 5.9 g/100 mL (15 °C)
Vapor pressure: 10−5 mmHg (20 °C)
Acidity (pKa): 9.9
Magnetic susceptibility (χ): −64.63×10−6 cm3/mol
Structure
Dipole moment: 1.4±0.1 D
Pharmacology
ATC code: D11AX11 (WHO)

Appearance: White to off-white crystalline solid
Odor: Mild phenolic odor
Molecular Formula: C₆H₆O₂
Molecular Weight: 110.11 g/mol
Density: ~1.33 g/cm³ (at 25°C)
Melting Point: 170–173°C
Boiling Point: ~285°C (decomposes)
Solubility in Water: ~70 g/L (at 25°C)
Solubility: Soluble in ethanol, ether, and acetone
pKa: ~10.3 (phenolic hydroxyl groups)
Vapor Pressure: Very low at ambient temperature
Log Kow: ~0.59
Flash Point: ~165°C
Autoignition Temperature: ~515°C

Molecular Weight: 110.11 g/mol
Molecular Formula: C6H6O2
XLogP3: 0.6
Hydrogen Bond Donor Count: 2
Hydrogen Bond Acceptor Count: 2
Rotatable Bond Count: 0
Exact Mass: 110.036779430 g/mol
Monoisotopic Mass: 110.036779430 g/mol
Topological Polar Surface Area: 40.5 Ų
Heavy Atom Count: 8
Formal Charge: 0
Complexity: 54.9
Isotope Atom Count: 0
Defined Atom Stereocenter Count: 0
Undefined Atom Stereocenter Count: 0
Defined Bond Stereocenter Count: 0
Undefined Bond Stereocenter Count: 0
Covalently Bonded Unit Count: 1

Related compounds of 1,4-Hydroxy Benzene (Hydroquinone):
1,4-benzoquinone

Related benzenediols:
Pyrocatechol
Resorcinol

Names of 1,4-Hydroxy Benzene (Hydroquinone):

Preferred IUPAC name:
Benzene-1,4-diol

Other names:
Hydroquinone
Idrochinone
Quinol
4-Hydroxyphenol
1,4-Dihydroxybenzene
p-Dihydroxybenzene
p-Benzenediol