2-Ethylhexanol
2-Ethylhexanol, also known as 2-ethyl-1-hexanol, is a branched-chain primary alcohol with the molecular formula C₈H₁₈O and a molecular weight of 130.23 g/mol.[1] It appears as a clear, colorless to pale yellow liquid with a characteristic mild odor, possessing a boiling point of approximately 184°C and a low vapor pressure that indicates limited volatility.[2] This eight-carbon chiral compound is poorly soluble in water (about 1 g/L at 20°C) but highly miscible with most organic solvents, making it versatile for industrial applications.[1][2] Industrially, 2-ethylhexanol is produced via a multi-step process starting with the hydroformylation of propylene using carbon monoxide and hydrogen to form n-butyraldehyde, followed by aldol condensation of the butyraldehyde to produce 2-ethylhex-2-enal, dehydration, and finally hydrogenation to yield the alcohol, with subsequent distillation for purification.[1] This process, often conducted under controlled conditions (e.g., hydrogenation at 140–170°C and 10–30 bar), is a cornerstone of large-scale chemical manufacturing, with global production exceeding millions of tons annually to meet demand in downstream sectors.[3] The compound's primary use is as a key intermediate in synthesizing ester plasticizers, particularly di(2-ethylhexyl) phthalate (DEHP), which is essential for flexible polyvinyl chloride (PVC) products like cables, flooring, and medical tubing.[1] Additional applications include its role as a solvent in coatings and inks, a component in synthetic lubricants and defoamers, and a building block for adhesives, synthetic resins, and even as a flavor volatile in certain foods.[4][5] From a safety perspective, 2-ethylhexanol is classified as a flammable liquid (flash point around 78°C) and a skin and eye irritant, potentially causing respiratory irritation upon inhalation or dermatitis upon prolonged skin contact, though it poses low to moderate overall health risks under proper industrial hygiene practices.[6][7] It is not considered persistent, bioaccumulative, or toxic to aquatic life at typical exposure levels, but handling requires ventilation, protective equipment, and adherence to regulations like those from the EPA for inert ingredient use in pesticides.[4] Ongoing research focuses on optimizing production efficiency and exploring bio-based alternatives to reduce reliance on petrochemical feedstocks.[8]Structure and Nomenclature
Chemical Structure
2-Ethylhexanol has the molecular formula C₈H₁₈O.[1] Its condensed structural formula is CH₃(CH₂)₃CH(C₂H₅)CH₂OH, representing a linear hexane chain with an ethyl branch at the second carbon and a hydroxyl group at the first carbon.[1] As a primary alcohol, 2-ethylhexanol features the -OH group attached to a terminal (primary) carbon atom within a branched eight-carbon aliphatic chain.[1] The branching occurs via an ethyl substituent (-CH₂CH₃) at the 2-position of the hexyl backbone, which distinguishes it from straight-chain octanol isomers.[1] The carbon at the 2-position serves as a chiral center, bonded to four distinct groups: a hydrogen atom, the ethyl side chain, a butyl group (-CH₂CH₂CH₂CH₃), and the hydroxymethyl group (-CH₂OH).[1] This asymmetry results in two enantiomers, (R)-2-ethylhexan-1-ol and (S)-2-ethylhexan-1-ol.[9] Commercial 2-ethylhexanol is produced and supplied predominantly as a racemic mixture of these enantiomers.[9] In skeletal formula representations, the molecule is depicted as a zigzag chain for the main hexyl backbone, with the ethyl branch extending from the second carbon and the -CH₂OH terminating the chain, emphasizing the branched topology without explicit hydrogen atoms.[10] The IUPAC name, 2-ethylhexan-1-ol, systematically denotes the parent hexanol chain, the position of the ethyl substituent, and the primary alcohol functionality.[1]Naming Conventions
The International Union of Pure and Applied Chemistry (IUPAC) recommended name for this compound is 2-ethylhexan-1-ol.[1] It is commonly referred to as 2-ethylhexanol, often abbreviated as 2-EH in industrial and technical contexts, along with variants such as 2-ethyl-1-hexanol and 2-ethylhexyl alcohol.[11] A historical synonym is isooctanol, reflecting its status as a branched isomer of octanol.[12] The etymology of the name stems from its derivation as a primary alcohol based on hexan-1-ol, with an ethyl group attached at the 2-position, which together form a branched C8 chain.[1] This systematic designation is favored in modern chemical literature over older, less precise terms like octyl alcohol—originally used for both the linear 1-octanol and this branched form—to ensure clarity and avoid confusion in identification and classification.[12] For regulatory and database purposes, 2-ethylhexanol is uniquely identified by the Chemical Abstracts Service (CAS) Registry Number 104-76-7 and the European Community (EC) Number 203-234-3.[11] The nomenclature underscores the molecule's chiral center at the substituted carbon, though racemic mixtures are typical in commercial production.[13]Physical and Chemical Properties
Physical Properties
2-Ethylhexanol is a colorless, oily liquid with a mild, characteristic odor at room temperature.[14][13] The compound exhibits the following key physical properties under standard conditions:| Property | Value | Conditions |
|---|---|---|
| Boiling point | 184.7 °C | 760 mmHg |
| Melting point | −76 °C | - |
| Density | 0.833 g/cm³ | 25 °C |
| Refractive index | 1.430 | 20 °C (D line) |