TOLUHYDROQUINONE

Chemical Identity
Common Name: Toluhydroquinone
IUPAC Name: 2-Methylbenzene-1,4-diol
CAS Number: 95-71-6
Molecular Formula: C₇H₈O₂
Molecular Weight: 124.14 g/mol

Synonyms
Toluhydroquinone
2-Methylhydroquinone
THQ
p-Dihydroxytoluene
o-Methyl hydroquinone

Molecular Structure and Positional Specificity
Toluhydroquinone is a well-defined positional isomer of methylhydroquinone. 
In this compound, the methyl group is located at the 2-position (ortho) relative to one hydroxyl group on the aromatic ring.

This specific substitution pattern introduces steric hindrance, which:
Protects hydroxyl groups from rapid oxidation
Stabilizes phenoxy radicals formed during inhibition
Reduces uncontrolled side reactions
As a result, THQ exhibits superior selectivity compared to non-specific methylhydroquinone.

Physicochemical Properties
Appearance: Off-white to pale yellow crystalline solid
Solubility:
Good solubility in organic solvents
Limited water solubility
Thermal stability: High
Oxidation resistance: Significantly improved compared to HQ
THQ maintains structural integrity under prolonged heat exposure, making it ideal for industrial polymer systems.

Radical Scavenging and Stabilization Mechanism
Toluhydroquinone acts as a controlled radical inhibitor. Upon interaction with propagating radicals, THQ forms stabilized phenoxy radicals that are less likely to re-initiate polymer chains.
The ortho-methyl group:
Enhances steric shielding
Slows down redox cycling
Improves long-term inhibition performance
This controlled mechanism prevents runaway polymerization while allowing predictable processing behavior.

Industrial Applications
Toluhydroquinone is widely used as:
Primary polymerization inhibitor for:
Styrene
Vinyl monomers
Acrylic and methacrylic systems
Antioxidant in rubber, elastomers, and synthetic resins
Stabilizer in high-temperature processing environments
Intermediate in fine chemical and specialty synthesis

Industrial Preference and Commercial Importance
In modern industrial practice, Toluhydroquinone is the most commercially important methylated hydroquinone derivative. Due to its defined structure and reproducible performance, it is often explicitly specified in technical standards and supply contracts, unlike generic methylhydroquinone terminology.
THQ offers an optimal balance between:
Inhibition efficiency
Thermal stability
Color preservation
Process predictability

Conclusion
While methylhydroquinone represents a broad and sometimes ambiguous category of compounds, toluhydroquinone stands out as a chemically precise, industrially optimized inhibitor. Its positional specificity provides enhanced control over radical reactions, making it a preferred choice in polymer stabilization and antioxidant systems.

SAFETY INFORMATION ABOUT TOLUHYDROQUINONE

 
First aid measures:
Description of first aid measures:
General advice:
Consult a physician. 
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
 
If inhaled:
If breathed in, move person into fresh air. 
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately. 
Wash off with soap and plenty of water.
Consult a physician.
 
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
 
If swallowed:
Do NOT induce vomiting. 
Never give anything by mouth to an unconscious person. 
Rinse mouth with water. 
Consult a physician.
 
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
 
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment. 
 
Avoid breathing vapours, mist or gas. 
Evacuate personnel to safe areas.
 
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste. 
Keep in suitable, closed containers for disposal.
 
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
 
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place. 
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
 
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
 
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles. 
Faceshield (8-inch minimum). 
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
 
Skin protection:
Handle with gloves. 
Gloves must be inspected prior to use. 
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product. 
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. 
Wash and dry hands.
 
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
 
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls. 
 
If the respirator is the sole means of protection, use a full-face supplied air respirator. 
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so. 
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions. 
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
 
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company. 
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product