Eicosanoic Acid (506-30-9) Physical and Chemical Properties
Eicosanoic Acid
Straight-chain C20 saturated fatty acid used as a hydrophobic building block and surface modifier in formulation development, analytical standards, and materials research.
| CAS Number | 506-30-9 |
| Family | Long-chain saturated fatty acids |
| Typical Form | Powder or crystalline solid |
| Common Grades | BP, EP, JP, Reagent Grade |
Eicosanoic acid is a straight‑chain, saturated long‑chain fatty acid (20 carbon atoms) belonging to the saturated fatty acyl class. Structurally it consists of an unbranched hydrocarbon chain terminating in a carboxylic acid headgroup; the empirical composition is \(\ce{C20H40O2}\). Electronic structure is dominated by a highly nonpolar hydrocarbon tail and a single polar carboxyl terminus; this molecular amphiphilicity governs phase behaviour, interfacial activity and ionization chemistry. The carboxyl proton confers weak acidity (carboxylic acid chemistry) and the conjugate base (icosanoate/arachidate) forms salts and esters that significantly alter aqueous solubility and surfactant properties.
Physicochemical characteristics reflect the long alkyl chain: high lipophilicity, low aqueous solubility, substantial melting point as a crystalline solid at ambient conditions, and a propensity to form ordered monolayers and crystalline phases. Saturation (no C=C double bonds) reduces susceptibility to autoxidation relative to unsaturated fatty acids, while still allowing standard fatty‑acid transformations (esterification, saponification, salt formation, enzymatic β‑oxidation in biological systems). In industrial contexts the material is handled and supplied predominantly as the free acid or as salts/esters and is used where long‑chain hydrophobicity and a carboxyl functional group are required.
Common commercial grades reported for this substance include: BP, EP, JP, Reagent Grade.
Molecular Attributes
Molecular Weight and Composition
- Molecular formula: \(\ce{C20H40O2}\).
- Molecular weight: 312.5 (reported value).
- Exact/monoisotopic mass: 312.302830514.
- Heavy atom count: 22; formal charge: 0; complexity: 226.
- Hydrogen bond counts: hydrogen bond donor count = 1; hydrogen bond acceptor count = 2.
- Rotatable bond count: 18; topological polar surface area (TPSA) = 37.3.
- Physical description (experimental): reported as "Solid" or "White crystalline flakes" in supplier and reference data; conformer generation for 3D modelling is commonly disallowed because the long flexible alkyl chain produces excessive conformational freedom.
- Spectrometric and spectral identifiers: collision cross section (DT, [M‑H]−) reported as 184.8 \(\mathrm{\AA}^2\) (other reported DT values include 183.41, 186.36, 185.1, 185 and 185.9 \(\mathrm{\AA}^2\)); Kovats retention index on non‑polar columns reported in the range 2359–2380 (values: 2359, 2366, 2380). NMR and MS experimental datasets are available for structure confirmation: representative 1H NMR chemical shifts and GC–MS fragmentation patterns show expected long‑chain aliphatic resonances and prominent fragment ions (m/z 43, 57, 73).
- Ionization behaviour in LC–ESI experiments: measured ionization mode = Positive for one dataset, but multiple LC–MS reports use negative ESI with the precursor \([M-H]^-\) at m/z 311.2956; reported ionization efficiency logIE = 1.25 at pH = 2.7 (with MeCN 80% and formic acid additive in the referenced instrument conditions).
Chemical structure strings (canonical identifiers):
- SMILES: CCCCCCCCCCCCCCCCCCCC(=O)O
- InChI: InChI=1S/C20H40O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18-19-20(21)22/h2-19H2,1H3,(H,21,22)
- InChIKey: VKOBVWXKNCXXDE-UHFFFAOYSA-N
LogP and Amphiphilicity
- Computed XLogP3: 8.5 (reported).
- Reported experimental LogP: 9.29 (reported).
Interpretation and implications: - The very high LogP values reflect extremely low aqueous solubility and strong partitioning into nonpolar phases or lipid matrices. As a consequence, formulations and processes using the free acid require organic solvents, dispersion as solid particles, or conversion to more polar derivatives (salts, esters, glycolipids, surfactants) to achieve aqueous compatibility. - Amphiphilicity is highly headgroup‑driven: the single carboxylate head will ionize under basic conditions to \(\ce{C20H39O2^-}\) (icosanoate/arachidate), dramatically increasing water dispersibility and enabling surfactant behaviour when combined with counterions (e.g., sodium/potassium arachidates). In neutral and acidic aqueous media the material remains predominantly nonpolar and tends to crystallize or form hydrophobic aggregates. - The low TPSA (37.3) relative to molecular size indicates that the polar surface is limited to the terminal carboxyl group, consistent with surface‑active and monolayer‑forming behaviour at interfaces.
Biochemical Properties
Biosynthesis and Metabolic Context
Eicosanoic acid occurs naturally as a minor component in various vegetable oils (reported sources include peanut and corn oils) and in some plant tissues. It is classified as a C20 saturated fatty acid (FA 20:0) and participates in general lipid metabolism pathways. Within organisms it can be incorporated into glycerides (triacylglycerols, diacylglycerols), wax esters and membrane lipids, or converted to acyl‑CoA derivatives for catabolic processing.
Cellular and tissue notes: - Reported tissue location: placenta. - Cellular locations cited include cytoplasm, extracellular space and membrane-associated pools, consistent with roles as a structural lipid component and metabolic intermediate.
Reactivity and Transformations
- Esterification: the carboxyl group undergoes straightforward esterification to form fatty acid esters (methyl, ethyl esters, glycerides) used for derivatization, formulation or incorporation into lipid matrices.
- Saponification and salt formation: base hydrolysis produces the corresponding carboxylate salt (arachidate/icosanoate), which markedly increases water miscibility and may act as a surfactant.
- Oxidation: chemical autoxidation is less pronounced than for unsaturated fatty acids due to full saturation; however, terminal and subterminal oxidation reactions and microbial oxidation pathways can occur under strong oxidative conditions.
- Enzymatic metabolism: acyl‑CoA activation followed by β‑oxidation is the primary enzymatic route for chain shortening in biological systems; ω‑ and α‑oxidation can occur in specialized pathways.
- Physical transformations: crystallization and polymorphism are important for handling and formulation because the long alkyl chain supports ordered solid phases and high melting points relative to shorter fatty acids.
Stability and Degradation
Chemical and Enzymatic Degradation Pathways
- Chemical stability: the saturated alkyl chain confers resistance to peroxide‑initiated autoxidation compared with unsaturated analogues. Hydrolysis of esters and saponification under alkaline conditions proceed readily for esterified forms.
- Environmental and biological degradation: microbial biodegradation via β‑oxidation is the dominant removal pathway in biological systems and environmental matrices; degradation rates depend strongly on bioavailability (adsorption to soils or particles reduces rate) and formulation form (free acid vs. ester vs. salt).
- Thermal stability: high melting point and high boiling point (see experimental properties below) indicate thermal robustness for many processing operations, but decomposition at elevated temperatures or in the presence of strong oxidizers is possible.
- Photostability: saturated fatty acids show limited direct photochemical degradation compared with conjugated or polyunsaturated lipids; indirect photochemical processes mediated by photosensitizers can contribute to breakdown in surface waters or formulations exposed to light.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS Registry Number: 506-30-9
- EC number: 208-031-3
- UNII: PQB8MJD4RB
- ChEBI: CHEBI:28822
- ChEMBL: CHEMBL1173381
- DSSTox Substance ID: DTXSID1060134
- HMDB: HMDB0002212
- KEGG: C06425
- LIPID MAPS ID: LMFA01010020
Canonical structure strings:
- SMILES: CCCCCCCCCCCCCCCCCCCC(=O)O
- InChI: InChI=1S/C20H40O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18-19-20(21)22/h2-19H2,1H3,(H,21,22)
- InChIKey: VKOBVWXKNCXXDE-UHFFFAOYSA-N
Synonyms and Lipid Nomenclature
Reported name variants and synonyms appearing in supplier and curated listings include (selection): - arachidic acid - icosanoic acid - EICOSANOIC ACID - Arachic acid - n‑Eicosanoic acid - C20:0 - fatty acid 20:0 - eicosanoate - n‑eicosanoate - Elcosanoic Acid - arachate
(Additional depositor and vendor‑supplied synonyms exist in technical catalogs; the above list is a representative subset drawn from nomenclature variants reported for the substance.)
Industrial and Biological Applications
Roles in Formulations or Biological Systems
- Technical uses: employed as a long‑chain fatty acid intermediate or additive in lubricants and lubricant additives, adhesives and sealants, and as a finishing agent or softener. Its long hydrophobic chain makes it useful where surface modification or hydrophobicity enhancement is required.
- Cosmetic and personal care: reported classification as an emulsifying or conditioning ingredient in personal‑care formulations; evaluation by expert panels has concluded safety for certain uses when formulated to be non‑irritating and non‑sensitizing (use‑specific qualifications apply).
- Materials and speciality uses: used in the formation of organic thin films and reported in the production of liquid‑crystal systems and other applications where ordered long‑chain monolayers or crystalline fatty acid films are required.
- Food and natural occurrence: present as a minor component in several vegetable oils (peanut, corn, etc.) and can be encountered as a trace natural lipid in biological samples and food matrices.
- When aqueous compatibility is required, conversion to salts (saponification) or esterification is the standard route to produce usable derivatives; salts and esters have distinct physical and application profiles relative to the free acid.
If a concise application summary is required for an unusual niche use not listed above, no additional concise application summary is available in the current data context; in practice this substance is selected based on its general properties described above.
Safety and Handling Overview
- Hazard classification summaries reported for industrial submissions include skin irritation (H315), serious eye irritation (H319) and potential respiratory irritation (H335). Aggregated reported hazard statements (with reported occurrence percentages in notifications) include: H315, H319, H335.
- Precautionary statement codes reported include: P261, P264, P264+P265, P271, P280, P302+P352, P304+P340, P305+P351+P338, P319, P321, P332+P317, P337+P317, P362+P364, P403+P233, P405, and P501. These codes reflect common risk‑management measures such as avoiding inhalation of dust, using eye/skin protection, controlling exposure and appropriate cleanup/disposal.
- General handling guidance for long‑chain fatty acids:
- Use appropriate personal protective equipment (gloves, eye protection, lab coat) to avoid skin and eye contact; avoid inhalation of dust if handling powdered or flaked material.
- Work in a well‑ventilated area; control dust generation and accumulation when handling solids.
- Store in a cool, dry, well‑sealed container away from strong oxidizing agents and moisture‑sensitive reagents; minimize prolonged exposure to elevated temperatures to avoid decomposition or transformation.
- For spills, contain and recover material where practicable, avoid release to waterways, and follow facility waste‑management procedures.
- Toxicology summary (class context): n‑alkyl carboxylic acids display low acute oral, dermal and inhalation systemic toxicity in the majority of datasets; they are irritant to skin and eyes at higher concentrations or as mechanical dusts. Sensitization potential is generally low for saturated long‑chain fatty acids.
- For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
Handling and Storage of Lipid Materials
- Physical form: solid crystalline flakes at ambient temperature (melting point reported below), so bulk handling considerations include dust control and mechanical transfer methods appropriate for particulate solids.
- Storage conditions: recommended to be kept in tightly closed containers in a cool, dry, well‑ventilated place; protect from moisture and strong oxidizing substances. Long‑term storage of the free acid can lead to slow crystallization or polymorphic changes that may affect bulk flow; mild warming and controlled agitation are standard remediation measures.
- Compatibility: compatible with common organic solvents used for formulation (alkanes, chlorinated solvents, certain esters); avoid strong oxidizers and reactive metal catalysts without appropriate controls.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
