2-Allylphenol
[CAS 1745-81-9]

Identification

• Classification: Natural product >> Natural phenols
• Name: 2-Allylphenol
• Synonyms: o-Allylphenol; 2-(2-Propenyl)phenol
• Molecular Formula: C₉H₁₀O
• Molecular Weight: 134.18
• CAS Registry Number: 1745-81-9
• EC Number: 217-119-0
• SMILES: C=CCC1=CC=CC=C1O

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 1.022 g/mL (Expl.)
• Melting point: -6 °C (Expl.)
• Boiling point: 220.0 °C 760 mmHg (Calc.)^*, 220 °C (Expl.)
• Flash point: 88.9 °C (Calc.)^*, 88 °C (Expl.)
• Solubility: water: 7 g/L (20 °C ) (Expl.)
• Index of refraction: 1.548 (Calc.)^*, 1.546 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05;GHS06;GHS09 Danger
• Risk Statements: H301+H311-H301-H311-H314-H318-H411
• Safety Statements: P260-P262-P264-P264+P265-P270-P273-P280-P301+P316-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P321-P330-P361+P364-P363-P391-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1B	H314
Acute toxicity	Acute Tox.	3	H301
Acute toxicity	Acute Tox.	3	H311
Serious eye damage	Eye Dam.	1	H318
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H312
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1C	H314
Eye irritation	Eye Irrit.	2	H319

• Transport Information: UN 2923

Discovery and Applications

2-Allylphenol is an aromatic phenolic compound with the molecular formula C₉H₁₀O. It consists of a phenol ring bearing an allyl substituent at the ortho (2-) position relative to the hydroxyl group. The molecule combines an electron-rich aromatic system with a reactive unsaturated side chain, creating a structure with both aromatic and olefinic chemical characteristics.

The core structural element is the phenol framework, which consists of a benzene ring substituted with a hydroxyl group (–OH). The hydroxyl group strongly influences the electronic properties of the aromatic ring because the oxygen atom can donate electron density into the aromatic π-system through resonance. This electron donation increases electron density at specific positions of the ring and activates the aromatic system toward electrophilic substitution reactions.

At the 2-position of the aromatic ring is an allyl group (–CH₂–CH=CH₂). The allyl substituent contains a carbon–carbon double bond conjugated with an adjacent methylene carbon. Although the allyl group is not directly conjugated with the aromatic ring through a continuous π-system because of the intervening methylene group, it still contributes additional hydrophobic character and introduces a reactive unsaturated region into the molecule.

Because the allyl group is located adjacent to the hydroxyl substituent, the compound is classified as an ortho-substituted phenol. This substitution pattern creates steric interactions between the substituents and influences molecular geometry and intermolecular behavior. Rotation around the bond connecting the allyl group to the aromatic ring allows some conformational flexibility.

The hydroxyl group serves as both a hydrogen-bond donor and hydrogen-bond acceptor. This functionality significantly influences intermolecular interactions and physical properties such as boiling point and solubility. The aromatic ring itself contributes hydrophobic character, while the hydroxyl group introduces localized polarity.

From an electronic perspective, the molecule contains multiple regions of electron density. The aromatic ring possesses delocalized π-electrons, while the allylic double bond contains an additional localized π-system. The hydroxyl substituent further modifies the electron distribution through resonance donation and inductive effects.

Physicochemically, 2-allylphenol exhibits amphiphilic characteristics. The phenolic hydroxyl group contributes polarity and hydrogen-bonding capability, whereas the aromatic ring and allyl side chain provide nonpolar and hydrophobic properties. Overall, however, the aromatic hydrocarbon portion dominates the molecular structure.

Chemically, the phenolic hydroxyl group can participate in reactions such as esterification, ether formation, and oxidation. The allyl double bond can undergo typical alkene reactions, including hydrogenation, oxidation, electrophilic addition, and polymerization under suitable conditions. The aromatic ring can also undergo electrophilic substitution reactions, although its reactivity is strongly influenced by the hydroxyl substituent.

The allylic position adjacent to the double bond can display enhanced reactivity compared with ordinary alkyl positions because allylic intermediates can be stabilized through resonance. This can influence oxidation and substitution reactions occurring at the side chain.

Overall, 2-allylphenol is an ortho-substituted phenolic aromatic compound containing both a hydroxyl-functionalized benzene ring and an unsaturated allyl side chain. Its structure combines aromatic stability, hydrogen-bonding capability, and alkene reactivity within a single multifunctional molecular framework.

References

2026. The LOTUS Initiative for Open Natural Products Research: frozen dataset union wikidata (with metadata).
DOI: 10.5281/zenodo.5794106

2025. Investigating the synergistic cytotoxicity and apoptosis-inducing effects of eugenol derivatives in combination with docetaxel on PC3 human prostate cancer cells. Medical oncology (Northwood, London, England).
DOI: https://pubmed.ncbi.nlm.nih.gov/41379243