Decane
Decane, systematically named n-decane, is a straight-chain alkane hydrocarbon with the molecular formula C₁₀H₂₂, consisting of a linear chain of ten carbon atoms connected by single bonds and saturated with hydrogen atoms.[1] It appears as a colorless, odorless liquid at standard temperature and pressure, with a melting point of −29.7 °C and a boiling point of 174.1 °C.[1] Decane has a density of 0.73 g/cm³ at 20 °C, is insoluble in water (solubility <0.009 mg/L at 20 °C), but is miscible with many organic solvents such as ethanol, and its vapors are heavier than air.[1] As a flammable liquid with a flash point of 46 °C, it is incompatible with strong oxidizing agents and can form explosive mixtures with air.[1] Decane occurs naturally as a minor constituent in the paraffin fraction of crude oil and natural gas, comprising up to 1.8% by volume in some petroleum samples.[1] It is produced industrially through fractional distillation of petroleum or synthesis via methods like the Fischer-Tropsch process, and serves as a reference standard for higher alkanes in fuel analysis.[1] Key applications include its use as a solvent in organic synthesis reactions, a component in the manufacture of petroleum products, rubber, and paper, and as a surrogate fuel for studying jet engine performance and kerosene combustion due to its representation of longer-chain hydrocarbons in aviation fuels.[2][1] Safety concerns with decane primarily involve its flammability and potential for aspiration hazards, with exposure to high concentrations causing central nervous system depression or skin irritation; it is classified under GHS as a flammable liquid (H226) and aspiration hazard (H304).[1] Environmentally, it is harmful to aquatic life and degrades slowly in air via reaction with hydroxyl radicals (half-life approximately 35 hours).[1]Nomenclature and structure
Chemical formula and structure
Decane, particularly its unbranched form known as n-decane, has the molecular formula C_{10}H_{22} and the condensed structural formula \ce{CH3(CH2)8CH3}.[1] This represents a saturated hydrocarbon composed of ten carbon atoms and twenty-two hydrogen atoms, where the carbon chain is fully saturated with no multiple bonds.[3] n-Decane is classified as a straight-chain alkane, featuring a linear sequence of ten carbon atoms connected exclusively by single covalent bonds (C-C), with each carbon atom bonded to the appropriate number of hydrogen atoms via single C-H bonds to satisfy valence requirements.[1] This structure exemplifies the general characteristics of alkanes as saturated acyclic hydrocarbons, where the chain length of ten carbons distinguishes decane from shorter or longer homologues in the alkane series.[3] In structural representations, n-decane's bond-line notation (also known as skeletal formula) is commonly illustrated as a zigzag line depicting the nine C-C bonds connecting the ten carbon atoms, with terminal methyl groups implied and all hydrogen atoms omitted for clarity.[4] This simplified depiction highlights the unbranched, linear topology essential to its chemical identity. Decane exhibits 75 constitutional isomers in total, though the focus here remains on the straight-chain n-decane.[5]Naming conventions and isomers
The preferred IUPAC name for the unbranched chain isomer of C₁₀H₂₂ is decane, reflecting the systematic nomenclature for alkanes where the root "dec-" indicates ten carbon atoms and the suffix "-ane" denotes a saturated hydrocarbon.[1] This name applies specifically to n-decane, the straight-chain structure, while branched variants receive names based on the longest carbon chain with substituents indicated by prefixes such as "methyl-" or "ethyl-".[6] Historically, n-decane has been referred to as decyl hydride, an older term emphasizing its composition as a hydride of the decyl radical.[1] The term "decane" in scientific and industrial contexts typically refers to n-decane unless a specific isomer is indicated, distinguishing it from the broader set of compounds sharing the formula C₁₀H₂₂.[1] These compounds exhibit constitutional isomerism, where isomers differ in the bonding sequence of atoms, leading to varied chain lengths and branching patterns. In contrast, stereoisomerism—arising from different spatial arrangements of atoms—is absent in n-decane and most simple alkane isomers due to the lack of chiral centers or geometric constraints in acyclic structures; however, certain highly branched isomers may possess optical stereoisomers if they contain asymmetric carbons.[7] The total number of constitutional isomers for C₁₀H₂₂ is 75, encompassing unbranched, mono-branched, and multi-branched forms. Key examples of branched constitutional isomers include 2-methylnonane, which features a methyl group on the second carbon of a nine-carbon chain, and 2,2-dimethyloctane, with two methyl groups on the second carbon of an eight-carbon chain; these illustrate how branching reduces the longest chain length while maintaining the total carbon count.[8] Such nomenclature follows IUPAC rules prioritizing the longest continuous chain as the parent structure, with substituents numbered to yield the lowest possible locants.[6]Physical properties
Appearance and phase behavior
Decane is a colorless liquid at room temperature and standard pressure, exhibiting a characteristic gasoline-like odor.[9] Under standard conditions, decane exists in the liquid phase, with a melting point ranging from -30.5 °C to -29.2 °C and a boiling point between 173.8 °C and 174.4 °C. This phase behavior reflects its nonpolar molecular structure, which limits intermolecular forces and results in relatively low transition temperatures compared to more complex hydrocarbons.[10] The density of decane is 0.730 g/mL at 20 °C, contributing to its lower density than water and thus its tendency to float on aqueous surfaces. Its surface tension measures 0.0238 N/m, indicative of weak cohesive forces typical of nonpolar liquids.[10] Decane is insoluble in water due to its hydrophobic nature but readily soluble in organic solvents such as ethanol and ether.[1]Thermodynamic and spectroscopic properties
The standard molar entropy of liquid n-decane at 298 K is 364.6 J·K⁻¹·mol⁻¹.[11] The standard enthalpy of formation for the liquid phase is -300.9 kJ/mol at 298 K.[12] The enthalpy of vaporization is 51.42 kJ/mol at 25 °C.[1] The standard enthalpy of combustion for the liquid is -6778.33 ± 0.88 kJ/mol at 298 K.[12] Infrared spectroscopy of n-decane reveals characteristic absorption bands for aliphatic C-H stretching vibrations in the 2850–3000 cm⁻¹ region, including asymmetric CH₂ stretch near 2925 cm⁻¹ and symmetric CH₂ stretch near 2850 cm⁻¹, along with weaker C-C stretching modes around 800–1000 cm⁻¹.[13] These features are typical of long-chain alkanes and aid in structural confirmation. Proton NMR spectroscopy of n-decane in CDCl₃ displays distinct signals: a triplet at approximately 0.88 ppm (3H, terminal -CH₃ groups) and a multiplet at around 1.26 ppm (16H, -CH₂- groups), reflecting the symmetric chain structure with equivalent methylene environments in the interior.[14] The refractive index of n-decane is 1.4102 at 20 °C.[1] Its dynamic viscosity is 0.838 mPa·s at 25 °C, decreasing to 0.359 mPa·s at 100 °C, indicative of typical alkane flow behavior.[1]| Property | Value | Conditions | Source |
|---|---|---|---|
| Standard enthalpy of formation (liquid) | -300.9 kJ/mol | 298 K | NIST |
| Enthalpy of vaporization | 51.42 kJ/mol | 25 °C | PubChem |
| Enthalpy of combustion (liquid) | -6778 kJ/mol | 298 K | NIST |
| Refractive index | 1.4102 | 20 °C | PubChem |
| Viscosity | 0.838 mPa·s | 25 °C | PubChem |