Anethole (4180-23-8) Physical and Chemical Properties
Anethole
A methoxy-substituted aromatic ether (anisole derivative) sourced from anise and fennel, used commercially as a flavor/fragrance ingredient and as a synthetic intermediate for specialty chemical applications.
| CAS Number | 4180-23-8 |
| Family | Methoxybenzenes (anisole derivatives) |
| Typical Form | Colorless liquid or crystalline solid |
| Common Grades | BP, EP, FCC, JP, USP |
Anethole is a phenylpropene-class aromatic ether, formally a para-substituted monomethoxybenzene: the molecular formula is \(\ce{C10H12O}\). Structurally it comprises a methoxy group on a benzene ring at the para position with a conjugated propenyl side chain (predominantly the trans/(E) isomer). The substituent pattern and conjugation confer an extended π-system with modest electron donation from the methoxy oxygen into the aromatic ring, producing an electron-rich aromatic ether that is stabilised by resonance but retains an exposed olefinic site.
Electronically and physically, anethole is a lipophilic, low-polarity small molecule (topological polar surface area \(9.2\), XLogP \: \(3.3\)) with a single hydrogen-bond acceptor (the ether oxygen) and no hydrogen-bond donors. These attributes favour passive diffusion across biological membranes, low water solubility, and partitioning into organic phases and lipids. The para-conjugated propenyl substituent increases susceptibility to electrophilic and oxidative transformations (notably O‑demethylation and oxidation of the side chain), while the aryl ether functionality is generally resistant to rapid hydrolysis under neutral aqueous conditions.
In industry and formulation contexts anethole is valued for its sweet anise-like odor and flavor; it is a chief constituent of anise, star anise and fennel essential oils and is used as a flavoring and fragrance ingredient and an intermediate for anisaldehyde and related derivatives. Common commercial grades reported for this substance include: BP, EP, FCC, JP, USP.
Basic Physical Properties
Density
Reported density values (as provided): \(0.9882\) (NTP, 1992) — "Less dense than water; will float"; additionally \(0.9878\) @ \(20\ ^\circ\mathrm{C}/4\ ^\circ\mathrm{C}\) and a range \(0.983\text{–}0.988\). These values indicate a bulk liquid density slightly below that of water and consistent behaviour as a water‑immiscible organic phase in liquid–liquid separations.
Melting Point
Reported melting/deposition information includes \(70.4\ ^\circ\mathrm{F}\) (NTP, 1992) and \(21.3\ ^\circ\mathrm{C}\). Additional experimental entries list melting point \(21.35\ ^\circ\mathrm{C}\). The substance exists as a crystalline solid near \(21\text{–}23\ ^\circ\mathrm{C}\) (trans‑isomer) and is liquid above that temperature; therefore solid/liquid state at ambient depends on storage temperature and isomeric composition.
Boiling Point
Reported boiling data: \(454.1\ ^\circ\mathrm{F}\) at \(760\ \mathrm{mmHg}\) (NTP, 1992), and \(234\ ^\circ\mathrm{C}\). A distillation range of \(234\text{–}237\ ^\circ\mathrm{C}\) is also recorded for the trans‑isomer. These high boiling temperatures reflect the relatively low volatility of the neat material at atmospheric pressure.
Vapor Pressure
Measured/quoted vapor pressure entries: \(0.05\ \mathrm{mmHg}\) and \(5.45\ \mathrm{Pa}\) @ \(294\ \mathrm{K}\). The low vapor pressure corresponds to low but non-negligible volatility; material released to air will partition to the vapour phase over time, particularly at elevated temperature.
Flash Point
Reported flash points: \(195\ ^\circ\mathrm{F}\) (NTP, 1992) and \(90.1\ ^\circ\mathrm{C}\). These values categorise anethole as a combustible organic liquid; appropriate fire precautions and control of ignition sources are required in handling and storage.
Chemical Properties
Solubility and Phase Behavior
Solubility notes include descriptors "Slightly soluble" and "ALMOST WATER INSOL; MISCIBLE WITH CHLOROFORM & ETHER." A measured water solubility is reported as \(1.110\mathrm{E}{-1}\ \mathrm{g}\,\mathrm{l}^{-1}\) @ \(25\ ^\circ\mathrm{C}\). Solubility in ethanol is substantially higher (examples: 1:8 in 80% alcohol; 1:1 in 90% ethanol; 1 mL in 2 mL 96% alcohol). The combined data indicate limited aqueous solubility with good solubility in mid‑to‑nonpolar organic solvents (ethers, chloroform, alcohols), consistent with the molecule's low polarity and XLogP \(3.3\).
Phase behaviour: the trans isomer shows crystallisation near \(21\ ^\circ\mathrm{C}\) and is liquid above this; commercial samples may be solid or liquid depending on temperature and purity/isomer ratio.
Reactivity and Stability
Anethole is an aromatic ether with an allylic/alkenyl substituent; reactive tendencies include: - Oxidative O‑demethylation (biotransformation to para‑hydroxy derivatives and anisic acid) and oxidation of the propenyl chain to cinnamyl/cinnamic derivatives in biological and oxidative environments. - Relative resistance to aqueous hydrolysis (alkyl aryl ethers are generally hydrolytically stable under ambient conditions). - Sensitivity to light: recommendations to protect from light indicate photochemical or oxidative degradation pathways. Handling considerations therefore include exclusion of strong oxidisers and light and storage under inert atmosphere at reduced temperatures where long‑term stability is required.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\ce{C10H12O}\).
- Molecular weight: \(148.20\) (reported).
- Exact/monoisotopic mass: \(148.088815002\).
These molecular parameters are consistent with a mono‑oxygenated C10 aromatic ether.
LogP and Polarity
- XLogP (XLogP3): \(3.3\).
- Topological polar surface area (TPSA): \(9.2\).
- Hydrogen-bond donors: \(0\).
- Hydrogen-bond acceptors: \(1\).
- Rotatable bond count: \(2\).
The moderately high logP and low TPSA indicate significant lipophilicity and low aqueous solvation energy, consistent with observed partitioning into organic solvents and biological membranes.
Structural Features
Anethole contains a para‑methoxyphenyl core with an (E)‑configured propenyl substituent. Key structural points: - Aromatic methoxy group provides electron donation via resonance into the ring and a single H‑bond acceptor site (ether oxygen). - The conjugated propenyl side chain confers allylic reactivity and increased susceptibility to oxidation and metabolic O‑demethylation to para‑hydroxy species. - Defined bond stereocentre count: \(1\) (E/Z geometric isomerism on the double bond). The trans/(E) isomer is the dominant commercial form and is responsible for the characteristic olfactory properties.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 4180-23-8
- InChI:
InChI=1S/C10H12O/c1-3-4-9-5-7-10(11-2)8-6-9/h3-8H,1-2H3/b4-3+ - InChIKey:
RUVINXPYWBROJD-ONEGZZNKSA-N - SMILES:
C/C=C/C1=CC=C(C=C1)OC
Synonyms and Structural Names
Common synonyms and systematic names (selected from deposited synonym lists) include: trans‑anethole; p‑propenylanisole; 1‑methoxy‑4‑[(E)‑prop‑1‑enyl]benzene; anethol; anise camphor; (E)‑1‑(4‑methoxyphenyl)propene; p‑methoxy‑β‑methylstyrene. These names reflect the same para‑substituted methoxyphenylpropene scaffold and the prevalence of the trans/(E) stereochemistry in commerce.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Anethole is used extensively as a flavoring agent (foods, beverages, confectionery) and as a fragrance ingredient in perfumery, soaps and dentifrices; it is a chief natural constituent of anise, star anise and fennel essential oils. Reported industrial uses also include synthesis of anisaldehyde, use as a sensitizer in bleaching of photographic colors, and as an embedding material in microscopy. Industry sectors include flavor and fragrance manufacturing, food and beverage processing, cosmetics/personal care, and basic organic chemical manufacturing.
Role in Synthesis or Formulations
In synthetic chemistry, anethole serves as a feedstock/intermediate for aromatic aldehydes and related derivatives (e.g., anisaldehyde) and as a component in formulations where a sweet aniseed odor is desired. In formulations it is used at low concentrations as a flavor or fragrance active; solubility in ethanol and organic solvents facilitates incorporation into alcoholic beverages and perfumery matrices. Reported formulation grades noted in manufacturing records include USP (technical) and FCC (Food Chemicals Codex) types.
Common commercial grades reported for this substance include: BP, EP, FCC, JP, USP.
Safety and Handling Overview
Acute and Occupational Toxicity
Hazard summaries identify anethole as a skin sensitizer and potential irritant: reported GHS hazard statement codes include H317 — "May cause an allergic skin reaction." Occupational exposure can cause contact dermatitis in sensitised individuals. High‑dose animal studies report hepatotoxic and neurotoxic effects and, under certain experimental conditions, evidence of mutagenic or tumourogenic outcomes; such outcomes are dose‑ and exposure‑route dependent. Acute exposure routes of concern include dermal contact, inhalation of vapour/ aerosol and ingestion.
First aid guidance reported includes immediate flushing of eyes and skin after contact, removal from exposure for inhalation incidents, and avoidance of inducing emesis for significant ingestion — see product‑specific safety information in the SDS for precise instructions.
Storage and Handling Considerations
- Combustible liquid: keep away from ignition sources and hot surfaces; use grounding and bonding during transfer of bulk material.
- Protect from light and store in tightly closed containers under an inert atmosphere where long‑term stability is required; refrigerated storage is recommended in some handling recommendations.
- Minimise skin contact and inhalation exposure: use impervious gloves, protective clothing, eye protection and, where vapour exposure may occur, an appropriate organic vapour respirator. For laboratory weighing or dilution of the neat material, a NIOSH‑approved half‑face respirator with organic vapour cartridges and particulate filter is recommended in the cited handling guidance.
- Spill response: absorb small spills with inert material, collect contaminated absorbents for disposal in sealed containers, ventilate the area and avoid releases to waterways. For large spills, isolate and consider downwind evacuation per emergency guidance for combustible water‑immiscible liquids. For detailed safe handling, storage and transport requirements consult the product‑specific Safety Data Sheet (SDS) and applicable local regulations.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
