1,4-Benzoquinone (C₆H₄O₂), also known as para-quinone, is a bright-yellow crystalline compound with a sharp, irritating odour reminiscent of chlorine, bleach, or hot plastic.
It is the oxidised derivative of hydroquinone and exhibits multiple reactive properties:
As a ketone, it can form oximes.
As an oxidant, it yields dihydroxy derivatives.
As an alkene, it undergoes addition reactions typical of α,β-unsaturated ketones.
1,4-Benzoquinone is unstable under strong mineral acids or alkali, which can cause condensation and decomposition.
What is 1,4-Benzoquinone used for?
1,4-Benzoquinone is widely used across industrial and scientific applications, including:
Polyesters: as a polymerisation inhibitor
Hydroquinone production: as a raw material
Chemical synthesis: with trialkylboranes to produce alkyl-substituted hydroquinones
Fungicides: as a precursor
Analytical chemistry: as a reagent and oxidising agent in photography
Adhesives: as a formulation ingredient
Coal analysis: in dehydrogenation
Pharmaceuticals: in cortisone production and in complexes with barbiturates
Polymers and resins: as an additive
Leather tanning: as a tanning agent
Electrodes: in quinhydrone electrodes for pH determination
1,4-Benzoquinone is used in leather tanning as a chemical tanning agent, contributing to the processing and preservation of leather in products like footwear.
Sources and Routes of Exposure
Sources of Exposure
Occupational: Workers in dye, textile, chemical, tanning, and cosmetic industries may be exposed during manufacture or use.
Environmental: Inhalation exposure can also occur through tobacco smoke.
Routes of Exposure
Inhalation: absorption of vapours or particulates into the respiratory tract.
Ingestion: accidental ingestion in occupational or laboratory settings.
Health Risks
Acute Effects
Eyes: Inhalation of high levels is highly irritating, causing discolouration of the conjunctiva and cornea.
Skin: Dermal exposure may cause dermatitis, skin discolouration, and erythema.
Systemic effects: Animal studies report kidney effects following exposure.
Oral exposure: Acute tests in rats show 1,4-Benzoquinone has high acute toxicity.
Chronic Effects
Skin: Long-term dermal contact may lead to skin ulceration.
Respiratory/vision: Chronic inhalation exposure may result in visual disturbances.
Regulation: The U.S. EPA has not established a Reference Concentration (RfC) or Reference Dose (RfD).
Reproductive/Developmental Effects
No human or animal data currently available.
Cancer Risk
No human data available.
Older animal studies using dermal, inhalation, and subcutaneous exposure are insufficient to evaluate carcinogenicity.
EPA: not classified.
IARC: Group 3 — not classifiable as to human carcinogenicity.
Safety
First Aid Measures
Eye contact: Remove contact lenses if present. Flush eyes with plenty of water for at least 15 minutes (cold water may be used). Seek immediate medical attention.
Skin contact: Flush skin with water for at least 15 minutes while removing contaminated clothing and shoes. Apply an emollient if irritation persists. Wash clothing before reuse. Seek medical attention immediately.
Serious skin contact: Wash with disinfectant soap and cover with antibacterial cream. Seek urgent medical assistance.
Inhalation: Move the person to fresh air. If not breathing, give artificial respiration. If breathing is difficult, provide oxygen. Seek immediate medical help.
Serious inhalation: Evacuate the victim to a safe area. Loosen tight clothing. If breathing is difficult, administer oxygen. If not breathing, provide artificial respiration — but note the risk of direct mouth-to-mouth if the inhaled material is toxic. Use barrier devices where possible. Seek urgent medical attention.
Ingestion: Do not induce vomiting unless instructed by medical personnel. Never give anything by mouth to an unconscious person. Loosen tight clothing and seek medical attention immediately.
Fire and Explosion Information
May be combustible at high temperature.
Auto-ignition temperature: 560 °C (1040 °F).
Small fires: Use dry chemical powder.
Large fires: Use water spray, fog, or foam.
Dust hazard: Powdered 1,4-Benzoquinone is capable of causing a dust explosion.
Exposure Controls and Personal Protection
Engineering Controls
Use process enclosures, local exhaust ventilation, or equivalent controls to keep airborne concentrations below recommended limits.
If dust, fumes, or mist are generated, ensure ventilation keeps levels under exposure limits.
Personal Protective Equipment (PPE)
Routine handling:
splash goggles
synthetic apron
vapour/dust respirator (certified/approved)
gloves.
Large spills/emergencies:
splash goggles
full protective suit
vapour/dust respirator
Gloves
boots,
self-contained breathing apparatus (SCBA).
Suggested PPE may not be sufficient in all conditions — consult a safety specialist before handling 1,4-Benzoquinone.
Regulation
United States
OSHA: The United States Occupational Safety & Health Administration has set the following Permissible Exposure Limit (PEL) for 1,4-Benzoquinone:
General Industry: 0.1 ppm, 0.4 mg/m3
Construction Industry: 0.1 ppm, 0.4 mg/m3 TWA
ACGIH: The American Conference of Governmental Industrial Hygienists has set a Threshold Limit Value (TLV) for 1,4-Benzoquinone of 0.1 ppm, 0.44 mg/m3 TWA
NIOSH: The National Institute for Occupational Safety and Health has set a Recommended Exposure Limit (REL) for 1,4-Benzoquinone of 0.1 ppm TWA
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