Hexene (4050-45-7) Physical and Chemical Properties
Hexene
Linear C6 olefin used as a volatile solvent and intermediate in petrochemical synthesis, formulation and organic synthesis workflows.
| CAS Number | 4050-45-7 |
| Family | Aliphatic alkenes |
| Typical Form | Colorless liquid |
| Common Grades | EP, JP, Technical Grade |
Hexene is an unsaturated aliphatic hydrocarbon (C6 olefin) belonging to the class of linear mono‑alkenes. The structure contains one C=C double bond within a six‑carbon backbone; the entry studied here corresponds to the (E)-2‑hexene connectivity (SMILES: CCC/C=C/C) and has molecular formula C6H12. As a terminally internal alkene, the molecule has limited polarity (topological polar surface area = 0) and no hydrogen‑bond donor or acceptor functionality, producing low aqueous solubility and appreciable hydrocarbon solubility.
Electronically the C=C bond defines the primary reactive locus: it confers π‑electron density susceptible to electrophilic addition, oxidative transformation, and catalytic insertion reactions. The molecule is non‑polar to weakly polar and moderately lipophilic (XLogP3 = 2.6), consistent with ready partitioning into organic phases and limited water miscibility. Hexene displays typical alkene reactivity (hydrogenation, halogenation, hydroformylation, epoxidation, hydroboration–oxidation) and is prone to radical polymerization or oligomerization under initiation conditions; it does not undergo simple hydrolysis under neutral conditions.
Industrial relevance derives from its role as a C6 olefin in petrochemical streams: it is produced in C6–C8 olefin cuts and is used as a chemical intermediate and comonomer in polyolefin manufacture, and as a feedstock for surfactant and detergent intermediates. Common commercial grades reported for this substance include: EP, JP, Technical Grade.
Physical Properties
Density and Phase
Physical form: gas or vapor at low pressure; commercially handled as a clear, colorless liquid with a mild odor at ambient conditions. Reported isomer‑specific densities at 20 \(\mathrm{^\circ C}\) include: 0.6869 \(\mathrm{g}\,\mathrm{cm}^{-3}\) (2‑Hexene (E)); 0.6772 \(\mathrm{g}\,\mathrm{cm}^{-3}\) (2‑Hexene (Z)); 0.6796 \(\mathrm{g}\,\mathrm{cm}^{-3}\) (3‑Hexene (Z)). The low liquid density is typical for C6 hydrocarbons and is consistent with volatility and vapor pressure data below.
Melting Point
Reported melting points are isomer dependent: -133 \(\mathrm{^\circ C}\) (2‑Hexene (E)); -141.1 \(\mathrm{^\circ C}\) (2‑Hexene (Z)); -115.4 \(\mathrm{^\circ C}\) (3‑Hexene (E)); -137.8 \(\mathrm{^\circ C}\) (3‑Hexene (Z)). These very low melting temperatures reflect the small, flexible hydrocarbon structure and weak intermolecular interactions.
Boiling Point
Reported boiling points (isomer specific): 67.9 \(\mathrm{^\circ C}\) (2‑Hexene (E)); 68.8 \(\mathrm{^\circ C}\) (2‑Hexene (Z)); 67.1 \(\mathrm{^\circ C}\) (3‑Hexene (E)); 66.4 \(\mathrm{^\circ C}\) (3‑Hexene (Z)). These values are consistent with volatile C6 olefins used in solvent blends and fuel fractions.
Vapor Pressure
Measured vapor pressures show that hexenes are significantly volatile. Representative experimental values include 173 \(\mathrm{mmHg}\), and additional reported values of 150.0 \(\mathrm{mmHg}\) and 155.0 \(\mathrm{mmHg}\); one explicit statement reads: vapor pressure = 173 \(\mathrm{mmHg}\) @ 25 \(\mathrm{^\circ C}\). The relatively high vapor pressure at ambient temperature explains rapid evaporation and potential for vapor accumulation in confined spaces.
Viscosity
No experimentally established value for this property is available in the current data context.
Chemical Properties
Flammability and Combustion
Hexene is a highly flammable liquid and produces flammable vapor/air mixtures. Vapors can travel along surfaces and collect in low areas; ignition risks include sparks, hot surfaces, and open flames. Combustion produces carbon oxides and, depending on conditions, incomplete combustion products. Hexenes are also an aspiration hazard if ingested and can produce central nervous system effects (CNS depression) at high concentrations. Standard industrial precautions for flammable hydrocarbon liquids—intrinsically safe electrical equipment, grounding/bonding during transfers, and elimination of ignition sources—are appropriate.
Reactivity and Typical Transformations
The C=C double bond is the primary reactive functional group. Typical, well‑established transformations include: - Catalytic hydrogenation to hexane. - Electrophilic addition (halogenation, hydrohalogenation) to give alkyl halides. - Hydroformylation (oxo process) to produce aldehydes and subsequent alcohols after reduction. - Epoxidation and dihydroxylation to generate epoxides or vicinal diols. - Radical polymerization and oligomerization under initiation (thermal or catalytic) to produce higher molecular weight hydrocarbons used as fuel or chemical feedstocks. Oxidation by air (autoxidation) at elevated temperature or in presence of radical initiators can form peroxides and oxygenated impurities; therefore, inhibitors or inerting may be required for storage and processing. Alkenes do not hydrolyze under neutral aqueous conditions but participate in hydroboration–oxidation and other catalytic functionalization reactions under controlled conditions.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 4050-45-7
- InChI: InChI=1S/C6H12/c1-3-5-6-4-2/h3,5H,4,6H2,1-2H3/b5-3+
- InChIKey: RYPKRALMXUUNKS-HWKANZROSA-N
- SMILES: CCC/C=C/C
- Molecular formula: C6H12
- Molecular weight: 84.16 \(\mathrm{g}\,\mathrm{mol}^{-1}\)
- XLogP3‑AA: 2.6
- UNII: 2TZ30GGG1A
- ChEBI: CHEBI:137755
- DSSTox: DTXSID90881224
- EC numbers reported in association with this connectivity: 223-752-3, 246-768-2
Synonyms and Structural Names
Common synonyms and structural names appearing in supplier and regulatory descriptors include: Hexene; Hexene, isomers; 2‑Hexene (cis + trans); (E)-hex-2-ene; (E)-2‑Hexene; trans-2‑Hexene; 2E‑Hexene; 2‑Hexene, (E)-. The connectivity corresponds to 2‑hexene isomers (cis/trans) and related 3‑hexene isomers depending on positional isomerism.
Industrial and Commercial Applications
Use as Solvent or Fuel Component
Hexene is present in C6–C8 olefin distillation cuts and is used as a volatile hydrocarbon solvent component and as a light fuel blend component in refinery streams. Its volatility and moderate lipophilicity make it suitable as a processing solvent or diluent in petrochemical operations when low polarity and high volatility are required.
Representative Use Scenarios
Representative industrial scenarios include: - Comonomer feedstock or intermediate in polyolefin production and polymer modification processes. - Chemical intermediate for alkylation, hydroformylation, and other catalytic transformations to produce aldehydes, alcohols, or surfactant intermediates. - Component of olefin streams sold to downstream chemical manufacturers (e.g., surfactant and detergent intermediate production). If specific application parameters are required (e.g., purity, impurity profile), selection should be guided by product specifications and intended downstream chemistry.
Safety and Handling Overview
Flammability Hazards
Hexene is classified as a highly flammable liquid and vapor. Vapors can form explosive mixtures with air and may be heavier than air, accumulating in low‑lying areas. Firefighting for hydrocarbon fires involves foam, dry chemical, or carbon dioxide extinguishers; water can be used as a spray to cool containers but may not extinguish the flame. Combustion and thermal decomposition generate hazardous gases including carbon monoxide and carbon dioxide.
Storage and Handling Considerations
Handle hexene in well‑ventilated areas with explosion‑proof electrical equipment. Implement grounding and bonding during transfers to prevent static discharge. Store in cool, dry, well‑ventilated flammable storage designed for hydrocarbon liquids, separated from strong oxidizers and acids. Use closed transfer systems where possible and control spill release using appropriate secondary containment. Personnel should wear suitable PPE (splash goggles, chemical‑resistant gloves, flame‑resistant clothing as required) and use respiratory protection if exposure limits may be exceeded. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
Acute toxicity data: LC50 (mouse, inhalation, 2 h) reported as \(40{,}000\,\mathrm{ppm}\). Reported health effects include skin and eye irritation, respiratory tract irritation at elevated concentrations, and CNS depression at high inhalation exposures. Ingestion carries an aspiration risk and potential pulmonary damage.
For disposal, transport and emergency procedures follow applicable local regulations and industry best practices for flammable hydrocarbon liquids; emergency responders should isolate the area, eliminate ignition sources, and use appropriate extinguishing agents and protective equipment.
