1-Hexene
1-Hexene is an organic compound classified as an alpha-olefin, with the molecular formula C₆H₁₂ and the structural formula CH₂=CH(CH₂)₃CH₃.[1][2] It appears as a clear, colorless liquid with a petroleum-like odor, exhibiting a density of 0.678 g/mL at 25 °C, a boiling point range of 60–66 °C, and a flash point of -26 °C (-15 °F) (closed cup).[1][2][3] Insoluble in water but soluble in organic solvents such as alcohol, benzene, chloroform, and ether, 1-hexene is primarily utilized as a comonomer in the copolymerization of ethylene to produce linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), enhancing the strength and flexibility of these plastics.[1][2][4] Industrially, 1-hexene is produced predominantly through the selective oligomerization, specifically trimerization, of ethylene using transition metal catalysts, such as chromium-based systems, which yield high selectivity for the alpha-olefin; global production reached approximately 1.59 million tonnes in 2024.[5][6][7] Alternative methods include its derivation as a byproduct from Fischer-Tropsch synthesis or dehydration of 1-hexanol derived from biomass, though these contribute less to global supply compared to ethylene-based processes.[5][8] This production is critical for the petrochemical industry, with major manufacturers such as Formosa Plastics employing proprietary catalyst technologies to achieve purities exceeding 99% for commercial applications; in November 2025, Formosa announced a $150 million investment for a new 1-hexene plant in Texas.[6][9] Beyond polyethylene resins used in films, pipes, and packaging, 1-hexene finds applications in the synthesis of surfactants (such as detergent alcohols and alkyl aromatics), plasticizers, oxo-alcohols, and lubricants, contributing to products in detergents, coatings, and personal care items.[10][2] It also serves as a solvent and reaction medium in organic synthesis, including the production of flavors, perfumes, dyes, and specialty resins, though these uses represent a smaller fraction of its overall demand.[1][2] Due to its flammability and potential environmental release during manufacturing, handling protocols emphasize ventilation and avoidance of ignition sources.[1]Sources and Occurrence
Natural Sources
1-Hexene occurs naturally in trace amounts in various plants, primarily as a volatile organic compound in their emissions and essential oils. It has been detected in the flowers of Lonicera japonica (Japanese honeysuckle), where it contributes to the overall volatile profile, albeit at negligible concentrations approaching zero in analyzed extracts.[11] Similarly, 1-hexene is present in Oryza sativa (rice), listed among its metabolites in comprehensive phytochemical databases.[12] In fruits, trace levels appear in Vitis vinifera (common grape vine) and Prunus domestica (European plum), as part of their floral and fruit volatile compounds.[13] These occurrences underscore 1-hexene's minor role in biological systems.[1] As a volatile organic compound, 1-hexene may participate in plant aroma profiles, aiding in attracting pollinators or deterring herbivores through emission blends, though its specific contributions remain understudied due to low abundance.[1] Today, industrial production serves as the primary source of 1-hexene, far exceeding natural yields.[1]In Petroleum and Industrial Byproducts
1-Hexene occurs naturally in trace amounts within the light naphtha and gasoline fractions of crude oil.[14] These fractions, derived from the distillation of crude oil, contain a mixture of hydrocarbons including small proportions of olefins like 1-hexene, though alkanes predominate in straight-run naphtha.[15] In industrial processes, 1-hexene is generated as a byproduct during fluid catalytic cracking (FCC) units, where heavier hydrocarbon feedstocks are converted into gasoline and lighter products, resulting in C6 olefins such as 1-hexene comprising part of the gasoline fraction's composition, often around 10-11 wt% for total C6 olefins in FCC gasoline.[16] Similarly, steam cracking of heavier hydrocarbons produces 1-hexene among the higher olefins in the byproduct streams, alongside primary products like ethylene and propylene.[17] The isolation of 1-hexene from petroleum refining streams dates back to the mid-20th century, coinciding with the commercialization of catalytic and thermal cracking technologies that enabled the separation of valuable olefins from complex mixtures.[6] Early methods relied on distillation and extraction from cracking byproducts, such as those from wax cracking processes, before dedicated oligomerization routes became prevalent.[6]Structure and Properties
Molecular Structure
1-Hexene, with the IUPAC name hex-1-ene, has the molecular formula C₆H₁₂ and a molar mass of 84.16 g/mol.[18] Its structural formula is CH₂=CH-CH₂-CH₂-CH₂-CH₃, featuring a terminal carbon-carbon double bond between the first (C1) and second (C2) carbon atoms. The carbons involved in this double bond (C1 and C2) exhibit sp² hybridization, resulting in trigonal planar geometry with bond angles of approximately 120° around each of these carbons. The C=C double bond length is approximately 1.34 Å, shorter than a typical C-C single bond due to the presence of the pi bond. 1-Hexene shares the molecular formula C₆H₁₂ with numerous constitutional isomers, including positional alkene isomers such as cis- and trans-2-hexene and 3-hexene, where the double bond is located internally along the chain. Cyclic isomers, such as cyclohexane and methylcyclopentane, represent saturated ring structures without unsaturation. The terminal positioning of the double bond in 1-hexene sets it apart, enhancing its reactivity in polymerization and other reactions characteristic of alpha-olefins.[19]Physical Properties
1-Hexene appears as a clear, colorless liquid at room temperature, exhibiting a mild petroleum-like hydrocarbon odor.[1][20] The compound displays characteristic physical parameters indicative of a light alkene. Its density is 0.673 g/cm³ at 20 °C, reflecting the low mass density typical of unsaturated hydrocarbons.[21] The melting point is -139.8 °C, allowing it to remain liquid under ambient conditions, while the boiling point is 63.5 °C.[21] Viscosity measures 0.25 mPa·s at 25 °C, contributing to its fluid handling properties.[22] These values are summarized in the following table:| Property | Value | Conditions |
|---|---|---|
| Density | 0.673 g/cm³ | 20 °C |
| Melting point | -139.8 °C | - |
| Boiling point | 63.5 °C | 1 atm |
| Viscosity | 0.25 mPa·s | 25 °C |