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Quinol is produced by the oxidation of aniline or phenol, by the reduction of quinone, or from a reaction of acetylene and carbon monoxide.
Quinol 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.
Quinol, also known as hydroquinone, is an aromatic organic compound commonly used as a reducing agent and chemical intermediate.
CAS Number: 123-31-9
Molecular Formula: C6H6O2
Molecular Weight: 110.11
EINECS Number: 204-617-8
Synonyms: hydroquinone, 1,4-benzenediol, beta-quinol, 1,4-dihydroxybenzene, p-benzenediol, Hydroquinone, 99.5%, 99.5%;HYDROXYQUINOL;HYDROCHINONE;HYDROQUINONE;AKOS BBS-00004220;hydroquinone--1,4-benzenediol;Idrochinone;Melanex
Quinols chemical formula is C₆H₆O₂.
Quinol consists of a benzene ring substituted with two hydroxyl (–OH) groups in the para position.
Quinol belongs to the class of dihydroxybenzenes.
Quinol is specifically the para-isomer of dihydroxybenzene (1,4-dihydroxybenzene).
Its structure allows it to undergo reversible oxidation–reduction reactions.
Physically, quinol appears as a white crystalline solid.
It may darken upon exposure to air and light due to oxidation.
It is moderately soluble in water and more soluble in organic solvents.
Quinol exhibits strong reducing properties.
Quinol can be oxidized to benzoquinone in a reversible redox reaction.
This redox behavior underlies many of its applications.
The compound is chemically sensitive to light and oxygen.
Exposure can cause gradual oxidation and discoloration.
It is typically stored in tightly closed containers away from light.
Quinol plays an important role in industrial and laboratory chemistry.
Quinol is used as an intermediate in the production of dyes, polymers, and specialty chemicals.
Its reducing ability also makes it useful in photographic and analytical applications.
Biologically, hydroquinone is known for its skin-lightening properties in dermatology.
It inhibits melanin production by interfering with tyrosinase activity.
Its cosmetic use is regulated in many countries.
Quinol is best described as a redox-active aromatic diol.
Its importance lies in its reducing power, chemical versatility, and industrial applications.
Quinol is characterized by a reversible redox system with its oxidized form, benzoquinone.
This redox pair plays an important role in both industrial chemistry and biological systems.
The interconversion between hydroquinone and quinone is widely studied in electrochemistry.
The compound exhibits acidic phenolic properties.
The two hydroxyl groups can donate hydrogen ions under suitable conditions.
This contributes to its reactivity in oxidation and substitution reactions.
Quinol is known for its ability to act as an antioxidant.
It can donate electrons to neutralize reactive oxygen species.
This property explains its role as a stabilizer in certain formulations.
In polymer chemistry, quinol can function as a polymerization inhibitor.
It scavenges free radicals and prevents unwanted polymer formation.
This makes it useful in stabilizing monomers during storage.
The molecule is relatively small and planar, which allows it to participate in hydrogen bonding.
This affects its solubility and crystallization behavior.
Hydrogen bonding also influences its interaction with biological systems.
Quinol is sensitive to air oxidation, especially in alkaline solutions.
It may form colored oxidation products over time.
Proper storage under controlled conditions is essential to maintain purity.
In biochemical contexts, hydroquinone-type structures appear in electron-transport systems.
Related quinone/hydroquinone pairs are involved in cellular redox reactions.
This highlights its importance beyond industrial chemistry.
Molecular formula: C6H6O2
Molecular weight: 110.11 g/mol
Melting point: 172–175 °C
Boiling point: 285 °C
Density: 1.32 g/cm3
Bulk density: 600 kg/m3
Vapor density: 3.81 (vs air)
Vapor pressure: 1 mm Hg (132 °C)
Refractive index: 1.6320
Flash point: 165 °C
Storage temperature: Store below +30 °C
Solubility: H2O 50 mg/mL (clear)
Water solubility: 70 g/L (20 °C)
Form: Needle-like crystals or crystalline powder
Color: White to off-white
Odor: Odorless
pKa: 10.35 (20 °C)
Biological source: Synthetic
Sensitive: Air and light sensitive
Merck index: 14,4808
BRN: 605970
Henry’s law constant: <2.07 × 10⁻⁹ atm·m³/mol (20 °C, approx.)
Exposure limits: NIOSH REL ceiling 2 ppm; IDLH 50 ppm; OSHA PEL TWA 2 ppm; ACGIH TLV TWA 2 ppm
Stability: Stable; combustible; incompatible with strong oxidizing agents, strong bases, oxygen, ferric salts; discolors in air
Cosmetics ingredients functions: Fragrance; hair dyeing; reducing; antioxidant; bleaching
Cosmetic Ingredient Review (CIR): Hydroquinone (123-31-9)
InChI: 1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
InChIKey: QIGBRXMKCJKVMJ-UHFFFAOYSA-N
SMILES: Oc1ccc(O)cc1
LogP: 0.59 (20 °C)
Quinol, a colorless, hexagonal prism, has been reported to be a good antimitotic and tumor-inhibiting agent.
Quinol 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.
Quinol has historically been used in photographic development.
Its reducing action converts silver ions into metallic silver during image formation.
Although less common today, this use was once widespread.
Quinol is recognized as a versatile redox-active compound.
Its chemical behavior supports applications in synthesis, stabilization, photography, and biological research.
Quinol exhibits well-defined electrochemical behavior, making it useful in redox studies and analytical chemistry.
Quinols oxidation potential is predictable and reversible under controlled conditions.
This makes it a model compound in electrochemical research.
In materials science, quinol is used as a stabilizer for monomers such as styrene and acrylic derivatives.
By scavenging free radicals, it prevents premature polymerization during storage and transport.
This improves shelf life and product safety.
Quinol can participate in complexation and hydrogen-bonding interactions.
Quinols hydroxyl groups allow interaction with metal ions and polar molecules.
These interactions influence crystallization and reactivity.
The compound undergoes oxidative coupling reactions under certain conditions.
Such reactions can produce colored byproducts.
This explains why exposed hydroquinone may darken over time.
Quinol is relatively thermally stable under controlled conditions.
However, at elevated temperatures and in the presence of oxygen, oxidation accelerates.
This necessitates controlled storage environments.
In dermatological science, quinol’s action is linked to inhibition of tyrosinase, the enzyme responsible for melanin synthesis.
By reducing melanin formation, it lightens hyperpigmented areas.
Because of potential side effects, its cosmetic use is regulated.
Quinol has also been investigated in photochemical and antioxidant research.
Its ability to donate electrons makes it a useful probe molecule.
These studies help understand oxidative stress and radical reactions.
In synthetic chemistry, quinol can be converted into a variety of substituted aromatic derivatives.
Its two reactive hydroxyl groups allow further functionalization.
This versatility makes it a useful starting material.
Quinol is regarded as a chemically versatile, redox-active phenolic compound.
Its combination of reducing power, antioxidant behavior, and synthetic utility explains its wide application across industries and research fields.
Quinol 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).
Quinol 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.
Uses Of Quinol:
Quinol is a pigment-lightening agent used in bleaching creams.
Quinol 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.
Quinol 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.
Photographic reducer and developer; antioxidant; stabilizing agent for some polymers; intermediate in the manufacturing of some dyes and pigments; in cosmetic formulations.
Quinol is widely used as a polymerization inhibitor.
Quinol prevents unwanted radical polymerization in monomers such as styrene and acrylic compounds.
This improves storage stability and transport safety.
In photographic processing, quinol is used as a developing agent.
It reduces silver ions to metallic silver during image formation.
This application relies on its strong reducing ability.
Quinol is used in the manufacture of dyes and pigments.
Quinol serves as a chemical intermediate in synthesis processes.
Its aromatic and phenolic structure supports further modification.
In pharmaceutical and fine chemical synthesis, quinol acts as a building block.
Its hydroxyl groups allow functionalization and derivatization.
This supports production of specialty chemicals.
Quinol is applied in dermatology and cosmetic formulations for skin-lightening purposes.
It inhibits melanin production by interfering with tyrosinase activity.
Use is regulated due to safety considerations.
In antioxidant and stabilizer systems, quinol functions as a reducing agent.
It protects materials from oxidative degradation.
This is relevant in rubber, plastics, and chemical formulations.
Quinol is used in analytical chemistry and redox studies.
Its reversible oxidation to benzoquinone makes it a model compound.
This supports electrochemical and spectroscopic research.
In industrial chemical production, quinol serves as an intermediate in synthesis pathways.
Its reactivity allows formation of more complex aromatic compounds.
This makes it valuable in specialty chemical manufacturing.
Quinol is used wherever strong reducing capability, antioxidant behavior, or aromatic chemical versatility is required.
Quinol is used in rubber and elastomer stabilization.
It acts as an antioxidant to slow oxidative degradation of rubber materials.
This improves durability and service life.
In adhesive and coating formulations, quinol is used as a stabilizer.
It prevents premature polymerization during storage.
This ensures consistent application performance.
Quinol is applied in hair dye formulations as a chemical intermediate.
It participates in oxidation-based color development systems.
Its redox properties support controlled pigment formation.
In electrochemical systems and sensors, quinol is used as a redox reference compound.
Its reversible oxidation to benzoquinone allows calibration and study of electron-transfer processes.
This is important in analytical research.
Quinol is used in textile and leather processing as a reducing agent.
It helps control oxidative reactions in certain treatment steps.
These applications are specialized and controlled.
In laboratory synthesis, quinol is used to prepare quinones and other substituted aromatic compounds.
Its two hydroxyl groups provide reactive sites for derivatization.
This supports fine chemical production.
Quinol is applied in corrosion inhibition systems.
Its antioxidant behavior can help reduce oxidative metal degradation under specific conditions.
These uses are formulation-dependent.
In chemical education and research, quinol is often used as a model compound for studying oxidation–reduction mechanisms.
Its well-understood behavior makes it suitable for demonstration and analysis.
Quinol is selected in applications requiring radical inhibition, redox control, antioxidant protection, and aromatic chemical synthesis.
Safety Profile Of Quinol:
Quinol presents moderate to significant health hazards, particularly in concentrated or industrial forms.
It should be handled with care and appropriate protective measures.
Exposure risks are associated with irritation, sensitization, and systemic toxicity.
Skin contact may cause irritation, redness, and dermatitis.
Prolonged or repeated exposure can lead to allergic skin reactions.
Protective gloves and protective clothing are recommended.
Eye contact can cause severe irritation or damage.
Symptoms may include pain, redness, and blurred vision.
Immediate rinsing with plenty of water and medical attention are advised.
Inhalation of dust or vapors may cause respiratory irritation.
High exposure can result in coughing, throat discomfort, or systemic symptoms.
Adequate ventilation and dust control are necessary during handling.
Ingestion is harmful and may cause nausea, vomiting, abdominal pain, and systemic toxicity.
Large doses can affect blood chemistry and organ function.
Immediate medical care is required if swallowed.
Quinol is a strong reducing agent and can react with oxidizing agents.
It may undergo oxidation when exposed to air, producing potentially irritating byproducts.
Quinol should be stored away from light and strong oxidizers.
Chronic exposure has been associated with skin depigmentation and possible organ effects.
Regulatory agencies restrict its use in cosmetic products in many countries.
Occupational exposure limits are established to minimize risk.
