The Complete Guide to Xylene: Properties, Uses, Safety & How It Compares
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The Complete Guide to Xylene: Properties, Uses, Safety & How It Compares
Xylene is one of the most widely used aromatic solvents in the world—yet it is routinely confused with toluene, mislabeled on product shelves, and misunderstood by the people who handle it every day. Whether you are thinning industrial coatings, clearing tissue samples in a histology lab, or degreasing metal parts before finishing, xylene is likely part of your process. This guide covers everything you need to know: chemical properties, isomer differences, head-to-head comparisons with other industrial solvents, real-world applications, grading, and safe handling.
What Is Xylene?
Xylene (dimethylbenzene) is an aromatic hydrocarbon with the chemical formula C8H10 and CAS number 1330-20-7. Commercial xylene is a mixture of three structural isomers—ortho-xylene, meta-xylene, and para-xylene—plus a small percentage of ethylbenzene. It is a clear, colorless liquid with a sweet odor, insoluble in water but miscible with most organic solvents including acetone, MEK, ethanol, and diethyl ether.
The three isomers differ only in the position of the two methyl groups on the benzene ring:
| Isomer | Methyl Positions | Boiling Point | Typical % in Mixed Xylenes | Primary Industrial Use |
|---|---|---|---|---|
| ortho-Xylene (o-xylene) | 1,2 | 144°C | ~20% | Phthalic anhydride production |
| meta-Xylene (m-xylene) | 1,3 | 139°C | ~40–65% | Isophthalic acid, solvents |
| para-Xylene (p-xylene) | 1,4 | 138°C | ~20% | PET plastic & polyester fiber |
| Ethylbenzene | N/A | 136°C | ~6–20% | Styrene production |
Chemical & Physical Properties
| Property | Value |
|---|---|
| Chemical Formula | C8H10 (dimethylbenzene) |
| Molecular Weight | 106.16 g/mol |
| CAS Number | 1330-20-7 (mixed isomers) |
| Appearance | Clear, colorless liquid |
| Odor | Sweet, aromatic |
| Boiling Range | 137–144°C (279–291°F) |
| Melting Point | -47°C (-53°F) |
| Flash Point | 25°C (77°F) closed cup |
| Specific Gravity | 0.865 at 20°C |
| Refractive Index | 1.496 at 20°C |
| Vapor Pressure | 6.6 mmHg at 20°C |
| Solubility in Water | Practically insoluble (~175 mg/L) |
| Evaporation Rate | 0.76 (butyl acetate = 1) |
| KB Value | ~98 (strong solvency) |
| NFPA Ratings | Health: 2, Flammability: 3, Reactivity: 0 |
Xylene’s high KB value of ~98 makes it one of the strongest aromatic solvents available—dissolving resins, adhesives, coatings, and inks that weaker solvents cannot touch. Its moderate evaporation rate (slower than acetone, faster than mineral spirits) gives formulators a wide working window for coatings and paints.
Xylene vs. Toluene: What Is the Difference?
This is the most common question in solvent selection, and the answer is straightforward: xylene is stronger, slower, and has a higher boiling point. Toluene evaporates faster and works well for quick-drying applications, while xylene provides better solvency for heavy-bodied coatings and epoxies.
| Property | Xylene | Toluene |
|---|---|---|
| Formula | C8H10 | C7H8 |
| Molecular Weight | 106.16 | 92.14 |
| Boiling Point | 137–144°C | 111°C |
| Flash Point | 25°C | 4°C |
| Evaporation Rate | 0.76 | 2.0 |
| KB Value | ~98 | ~105 |
| Solvency Power | Excellent for heavy coatings | Excellent for light coatings |
| Working Time | Longer—slower evaporation | Shorter—faster evaporation |
| Odor Intensity | Moderate sweet | Strong sweet |
| Best For | Epoxies, urethanes, histology | Quick-drying lacquers, inks, adhesives |
Xylene vs. Other Industrial Solvents
| Solvent | KB Value | Evap Rate | Flash Pt | Toxicity | VOC? | Best Use Case |
|---|---|---|---|---|---|---|
| Xylene | ~98 | 0.76 | 25°C | Moderate | Yes | Heavy coatings, epoxies, histology |
| Toluene | ~105 | 2.0 | 4°C | Moderate | Yes | Fast-dry lacquers, inks |
| MEK | ~100 | 3.8 | -9°C | Low–Mod | Yes | Adhesives, resin dissolving |
| Acetone | ~100 | 5.6 | -20°C | Low | Exempt | Flash-off cleaning, degreasing |
| Mineral Spirits | ~30 | 0.1 | 38°C | Low | Yes | Gentle paint thinning, brush cleaning |
| n-Butyl Acetate | ~56 | 1.0 | 22°C | Low | Yes | Automotive clear coats |
| TCE | ~130 | 6.3 | N/A | High | No | Vapor degreasing (restricted) |
Xylene occupies a unique position: it is significantly stronger than mineral spirits and butyl acetate, competitive with MEK and toluene in solvency, but evaporates much slower—giving painters and applicators more working time. This is why it dominates in two-part epoxy systems, polyurethane coatings, and high-build industrial finishes where flash-off solvents like acetone would cause bubbling or poor leveling.
Industry Applications
Paints, Coatings & Adhesives
Xylene is the go-to thinner for epoxy coatings, polyurethane paints, alkyd enamels, and marine finishes. It dissolves binder resins, controls viscosity, and regulates dry time. Compare it against mineral spirits for your specific coating system.
Histology & Microscopy
The standard tissue-clearing agent in pathology labs worldwide. Xylene removes paraffin wax from tissue sections during slide preparation (deparaffinization) and acts as a clearing agent before coverslipping. ACS-grade purity is critical—trace impurities cause cloudy slides and staining artifacts.
Industrial Degreasing
Removes heavy grease, tar, bitumen, adhesive residues, and carbon deposits from metal surfaces before finishing. Often preferred over TCE in facilities transitioning to less-regulated solvents.
Chemical Synthesis
Used as a reaction medium and extraction solvent in organic chemistry. Xylene’s high boiling point allows reflux reactions at higher temperatures than toluene. Also a feedstock for phthalic anhydride (o-xylene) and terephthalic acid (p-xylene) in specialty chemical manufacturing.
Printing & Inks
A solvent carrier for gravure and flexographic inks, xylene dissolves resin binders and controls ink flow properties. Its moderate evaporation rate prevents premature drying on the press while still allowing fast set times on the substrate.
Electronics & PCB Manufacturing
Cleans flux residues, removes conformal coatings for rework, and dissolves photoresist in circuit board manufacturing. For precision electronics, see how xylene compares to low-residue solvents in AI hardware prep.
Grades & Specifications
Alliance Chemical offers xylene in two grades, each formulated for different quality requirements:
| Specification | ACS Reagent Grade | Technical Grade |
|---|---|---|
| Assay (Xylenes + Ethylbenzene) | ≥98.5% | ≥95% |
| Water Content | ≤0.05% | ≤0.1% |
| Residue After Evaporation | ≤0.005% | ≤0.01% |
| Acidity | ≤0.0003 meq/g | Not specified |
| Color (APHA) | ≤10 | ≤20 |
| Trace Metals | Minimal (meets ACS specs) | Not tested |
| Best For | Histology, HPLC, analytical labs | Paint thinning, degreasing, cleaning |
| Available Sizes | 1 Qt to 55-gal drums | 1 Qt to 55-gal drums |
Xylene in Histology: Why It Remains the Gold Standard
Despite decades of research into xylene substitutes, xylene remains the most widely used clearing and deparaffinization agent in pathology and histology labs. Here is why:
| Workflow Step | Xylene’s Role | Why Substitutes Fall Short |
|---|---|---|
| Deparaffinization | Dissolves paraffin wax from tissue sections in 2–5 minutes | Substitutes (d-limonene, aliphatic hydrocarbons) work slower and may leave residue |
| Clearing | Renders dehydrated tissue optically transparent (RI ~1.496 matches glass) | Many substitutes have different refractive indices, causing hazy slides |
| Coverslipping | Compatible with all standard mounting media (DPX, Permount, Entellan) | Some substitutes require specialized mounting media |
| Stain Differentiation | Consistent results with H&E, IHC, special stains | Substitutes may alter stain intensity or contrast |
For labs processing hundreds of slides daily, consistency matters more than anything. Xylene’s predictable refractive index (1.496), fast clearing speed, and universal compatibility with standard protocols make it irreplaceable for high-throughput diagnostic work. If you are evaluating xylene alternatives for safety reasons, the best approach is better ventilation and handling procedures—not a solvent swap that compromises diagnostic quality.
Safety & Handling
- CNS depressant: Acute inhalation causes headache, dizziness, nausea, and confusion. Chronic overexposure can cause neurological effects
- Skin absorption: Repeated skin contact causes drying, cracking, and dermatitis. Wear chemical-resistant gloves (nitrile or butyl rubber)
- Eye irritant: Wear splash goggles—xylene causes severe eye irritation on contact
- OSHA PEL: 100 ppm TWA (8-hour). ACGIH TLV: 100 ppm TWA, 150 ppm STEL
- Flammable liquid (Flash Point 25°C / 77°F)—Class IB flammable liquid per NFPA
- Static accumulation: Xylene has low conductivity. Ground and bond all containers during transfer to prevent static ignition
- Store in a flammable liquids cabinet, away from heat sources, sparks, and oxidizers
- Ventilation: Use in well-ventilated areas or under a fume hood. Local exhaust ventilation is required for continuous use
- Incompatibilities: Strong oxidizing agents, strong acids
For detailed storage requirements, see our guides on solvent storage safety and professional chemical storage. Always consult the Safety Data Sheet (SDS) before handling. Learn how to read chemical labels for proper hazard identification.
Get Xylene from Alliance Chemical
Available in quart, gallon, 5-gallon pails, and 55-gallon drums. ACS Reagent Grade and standard grade options. Fast shipping, bulk pricing, and expert support.
Shop Xylene | Shop ACS Grade Xylene | Browse All Hydrocarbon Solvents
Frequently Asked Questions
What is xylene used for?
Xylene is used primarily as a solvent in paints, coatings, adhesives, and inks; as a clearing agent in histology and pathology labs; for industrial degreasing of metal and equipment surfaces; and as a chemical feedstock for plastics manufacturing. It is one of the most versatile industrial solvents available.
Is xylene the same as toluene?
No. Xylene (C8H10) and toluene (C7H8) are both aromatic hydrocarbons, but xylene has two methyl groups while toluene has one. Xylene has a higher boiling point (137–144°C vs. 111°C), evaporates slower, and provides longer working time for coatings. Toluene is preferred when faster drying is needed.
Is xylene dangerous?
Xylene is a flammable liquid and a CNS depressant. It can cause headache, dizziness, and irritation at high concentrations. With proper ventilation, PPE (nitrile gloves, safety goggles), and adherence to OSHA exposure limits (100 ppm TWA), xylene is safely handled in thousands of industrial facilities and labs daily. See our storage and safety guide.
Can I use xylene to thin paint?
Yes—xylene is one of the best solvents for thinning oil-based paints, epoxies, polyurethanes, and varnishes. It provides excellent solvency and a longer working time compared to mineral spirits or toluene. Always follow the paint manufacturer’s recommendations for thinner type and ratio.
What is xylene ACS grade?
ACS (American Chemical Society) grade xylene meets strict purity standards (≥98.5% assay, minimal trace metals, low residue after evaporation) established by the ACS for laboratory and analytical use. It is required for histology, HPLC, and other precision applications. Learn more about chemical grades.
What can I use instead of xylene?
Depending on your application: toluene for faster evaporation; D-limonene as a greener degreasing alternative; MEK for aggressive resin dissolving; or mineral spirits for gentle paint thinning. In histology, some labs use d-limonene-based substitutes, though they have limitations (see our histology section above). See the complete solvent selection guide.
Frequently Asked Questions
What is xylene used for?
Xylene is used as a solvent in paints, coatings, adhesives, and inks; as a clearing agent in histology and pathology labs; for industrial degreasing; and as a chemical feedstock for PET plastic and polyester fiber manufacturing.
Is xylene the same as toluene?
No. Xylene (C8H10) has two methyl groups on the benzene ring while toluene (C7H8) has one. Xylene has a higher boiling point (137-144C vs 111C), evaporates slower, and gives longer working time for coatings. Toluene dries faster.
Is xylene dangerous?
Xylene is a flammable liquid and CNS depressant that can cause headache, dizziness, and irritation. With proper ventilation, PPE (nitrile gloves, safety goggles), and adherence to OSHA exposure limits (100 ppm TWA), it is safely handled in thousands of facilities daily.
Can I use xylene to thin paint?
Yes. Xylene is one of the best solvents for thinning oil-based paints, epoxies, polyurethanes, and varnishes. It provides excellent solvency and longer working time compared to mineral spirits or toluene. Follow paint manufacturer recommendations for ratios.
What is xylene ACS grade?
ACS grade xylene meets strict purity standards (98.5%+ assay, minimal trace metals, low residue) set by the American Chemical Society. It is required for histology, HPLC, and precision laboratory applications.
What can I use instead of xylene?
Alternatives depend on application: toluene for faster evaporation, D-limonene as a greener degreaser, MEK for aggressive resin dissolving, or mineral spirits for gentle paint thinning. In histology, d-limonene substitutes exist but have limitations.
What are the three isomers of xylene?
The three xylene isomers are ortho-xylene (1,2-dimethylbenzene, BP 144C), meta-xylene (1,3-dimethylbenzene, BP 139C), and para-xylene (1,4-dimethylbenzene, BP 138C). Commercial mixed xylenes contain all three plus ethylbenzene.
Why is xylene used in histology?
Xylene is the standard clearing and deparaffinization agent because its refractive index (1.496) closely matches glass, producing crystal-clear tissue sections. It dissolves paraffin quickly, works with all standard stains and mounting media, and gives consistent reproducible results.
