Ortho-xylene (CAS 95-47-6) and para-xylene (CAS 106-42-3) are two structural isomers of dimethylbenzene that are widely utilized as key aromatic intermediates in petrochemical production.
These two compounds share the same molecular formula (C₈H₁₀), yet they differ in the positioning of the two methyl groups on their benzene rings. It is precisely this structural difference that endows them with distinct physical properties and industrial applications within the realm of downstream chemical manufacturing.
What is O-Xylene?
CAS 95-47-6 o-Xylene (ortho-xylene) is an isomer of dimethylbenzene in which the two methyl groups are attached to adjacent substituent positions. If there are two substituents attached to two adjacent carbon atoms of benzene, we call this configuration "ortho" configuration. Therefore, the name O-xylene originates from the name "ortho-xylene". This is a constitutional isomer of para and meta configurations of dimethylbenzene. O-xylene occurs as a liquid at room temperature. It is a colourless liquid which is slightly oily and highly flammable.
o-Xylene (Ortho-Xylene) Properties Table
| Property | Properties |
|---|---|
| Chemical Formula | C₈H₁₀ |
| CAS Number | 95-47-6 |
| Molecular Structure | 1,2-dimethylbenzene (adjacent methyl groups) |
| Physical State | Colorless liquid |
| Odor | Aromatic, sweet, gasoline-like |
| Boiling Point | ~144°C |
| Melting Point | ~-25°C |
| Density (20°C) | ~0.88 g/cm³ |
| Solubility in Water | Insoluble |
| Vapor Pressure | Moderate (volatile organic compound) |
| Flash Point | ~29°C |
| Hazard Class | Flammable liquid, irritant VOC |
Ortho-xylene is an aromatic hydrocarbon intermediate primarily used as a feedstock for downstream oxidation processes.
In industrial production, o-xylene undergoes catalytic oxidation to yield phthalic anhydride (PA); phthalic anhydride is a key intermediate widely utilized in the manufacture of plasticizers and resin materials.
Phthalic anhydride can be further processed to produce:
- Phthalate plasticizers for PVC modification
- Unsaturated polyester resins (UPR) for use in glass fiber-reinforced plastics, coatings, and composite materials
Related Article: What Is Ortho-Xylene (CAS 95-47-6) Used For? Applications and Benefits
What is P-Xylene?
CAS 106-42-3 P-xylene is an isomer of dimethylbenzene, with the two methyl groups attached to opposite positions of the substituents. If two substituents are attached to two opposite carbon atoms of benzene, this is called the 'para' configuration. Therefore, the name p-xylene derives from para-xylene. It is also a constitutional isomer of the ortho and meta configurations of dimethylbenzene. P-xylene is a colourless, highly flammable liquid at room temperature.
Para-xylene (PX) Properties
| Property | Properties |
|---|---|
| Chemical Formula | C₈H₁₀ |
| CAS Number | 106-42-3 |
| Molecular Structure | 1,4-dimethylbenzene (opposite methyl groups) |
| Physical State | Colorless liquid |
| Odor | Aromatic, sweet hydrocarbon smell |
| Boiling Point | ~138°C |
| Melting Point | ~13°C |
| Density (20°C) | ~0.86 g/cm³ |
| Solubility in Water | Insoluble |
| Vapor Pressure | Moderate to high volatility |
| Flash Point | ~25°C |
| Hazard Class | Flammable liquid, VOC |
Para-xylene is a key aromatic intermediate, primarily used as a feedstock for the production of purified terephthalic acid (PTA) via catalytic oxidation.
PTA is subsequently utilized in the manufacture of polyethylene terephthalate (PET), a material widely applied in:
- PET bottles
- Polyester fibers
- Packaging films
In petrochemical production, paraxylene is a significant C8 aromatic isomer, the demand for which is primarily driven by the global PET and polyester value chains.
What is the difference between o-Xylene and p-xylene?
| Feature | o-Xylene CAS 95-47-6 | p-Xylene CAS 106-42-3 |
| Molecular Structure | Methyl groups at 1,2-position (adjacent) | Methyl groups at 1,4-position (opposite) |
| Main Production Route | Catalytic reforming, pyrolysis gasoline separation | Catalytic reforming, selective adsorption/isomer separation |
| Primary Use | Phthalic anhydride (PA) | Terephthalic acid (PTA) |
| Downstream Products | Plasticizers, alkyd resins, UPR materials | PET resin, polyester fiber, packaging materials |
| Boiling Point | ~144°C | ~138°C |
| Melting Point | -25 °C (-13 °F) | 13 °C (55 °F) |
| Molecular Symmetry | Low symmetry | High symmetry |
Key Differences Explained
Para-xylene is structurally more symmetrical than ortho-xylene, and this difference directly affects their physical behavior, separation methods, and industrial use.
1. Symmetry and melting behavior:
p-xylene has a highly symmetrical 1,4-substitution pattern, which allows efficient crystal packing and results in a relatively high melting point (solidification around 13°C). In contrast, the 1,2-substitution in o-xylene reduces symmetry, preventing tight molecular packing, so it remains liquid at much lower temperatures (around -25°C).
2. Boiling point & separation:
Their boiling points are close (p-xylene ~138°C, o-xylene ~144°C), making conventional fractional distillation ineffective for separation. Industrial separation typically relies on adsorption-based processes or crystallization techniques, which provide higher selectivity for xylene isomers.
3. Industrial application:
CAS 95-47-6 o-xylene chemical is mainly converted to phthalic anhydride (PA) for use in plasticizers and resin systems, while CAS 106-42-3 p-xylene is the primary feedstock for terephthalic acid (PTA), which is further used in polyester fibers and PET plastic production.
Frequently Asked Questions (FAQ)
Q: What is o-xylene mainly used for?
CAS 95-47-6 o-xylene chemical is mainly oxidized to produce phthalic anhydride (PA), an intermediate used in plasticizers, alkyd resins, and unsaturated polyester resins.
Q: What is p-xylene mainly used for?
p-xylene (PX) is used as the primary feedstock for producing terephthalic acid (PTA), which is further used to manufacture PET plastics and polyester fibers.
Q: Why is p-xylene more commercially valuable?
Because it is directly linked to the PET value chain, which is one of the largest polymer markets globally, especially in packaging and textile industries.
Q: Why is o-xylene liquid at room temperature but p-xylene can solidify?
p-xylene has a symmetrical molecular structure that allows strong crystal packing, giving it a higher melting point, while o-xylene has an asymmetric structure that prevents solid formation under normal conditions.
Q: Can o-xylene and p-xylene be separated by distillation?
No. Their boiling points are very close, so industrial separation requires fractional crystallization or adsorption-based separation technologies rather than simple distillation.
Q: Are o-xylene and p-xylene hazardous chemicals?
o-Xylene and p-Xylene are flammable aromatic hydrocarbons classified as VOCs. They can cause irritation and pose fire hazards under improper handling conditions.
Q: What protective equipment is required when handling xylene?
Standard industrial handling requires chemical-resistant gloves, safety goggles, protective clothing, and adequate ventilation or respirators in confined areas.
Q: What packaging is commonly used for xylene transportation?
Industrial xylene is typically packaged in:
- Steel drums (200L)
- IBC tanks (1000L)
- ISO tank containers for bulk transport
Related Article: Bulk O-Xylene Solvent CAS 95-47-6: Specifications, Packaging, and Global Supply
Q: Are They compatible with plastic containers?
They are generally not recommended for long-term storage in certain plastics, as aromatic solvents may cause swelling or permeation. Steel containers are preferred for industrial use.
about us
Gneebio is a chemical supplier with partnerships with numerous manufacturing plants. The company specializes in supplying aromatics, solvents, and chemical intermediates, which have wide applications in downstream industries.
We focus on providing a stable bulk supply, consistent product specifications, and complete technical documentation, including COA, SDS, and TDS, to support industrial procurement and compliance requirements in international trade.
