3-Propylphenol
[CAS 621-27-2]

Identification

• Classification: Flavors and spices >> Synthetic spice >> Phenols, ethers and epoxides
• Name: 3-Propylphenol
• Molecular Formula: C₉H₁₂O
• Molecular Weight: 136.19
• CAS Registry Number: 621-27-2
• EC Number: 210-675-5
• SMILES: CCCC1=CC(=CC=C1)O

Properties

• Density: 1.0$+/-$0.1 g/cm³ Calc.^*
• Melting point: 26 $degree$C (Expl.)
• Boiling point: 229.8$+/-$9.0 $degree$C 760 mmHg (Calc.)^*, 229 - 231 $degree$C (Expl.)
• Flash point: 108.8$+/-$8.8 $degree$C (Calc.)^*
• Index of refraction: 1.529 (Calc.)^*

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

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302+H312-H302-H312-H314-H317-H318-H332-H335
• Safety Statements: P260-P261-P264-P264+P265-P270-P271-P272-P280-P301+P317-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P319-P321-P330-P333+P317-P362+P364-P363-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H312
Skin corrosion	Skin Corr.	1C	H314
Skin sensitization	Skin Sens.	1B	H317
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H332

Discovery and Applications

3-Propylphenol is an aromatic phenolic compound with the molecular formula C₉H₁₂O. It consists of a benzene ring bearing a hydroxyl group (–OH) and a propyl substituent (–CH₂CH₂CH₃) at the 3-position (meta position relative to the hydroxyl group).

Structurally, the compound belongs to the alkylphenol family. The phenolic hydroxyl group defines its basic chemical behavior, while the propyl side chain modifies its hydrophobicity and steric environment. Because the substituents are arranged in a meta relationship, there is no strong intramolecular interaction between the hydroxyl group and the alkyl chain, leaving both functional regions relatively independent in terms of reactivity.

The phenolic –OH group is the most chemically active site. It can undergo typical phenol reactions such as esterification, etherification, oxidation to quinone-like structures, and deprotonation to form phenoxide ions under basic conditions. The acidity of the hydroxyl group is influenced by the electron-donating effect of the propyl substituent, which slightly reduces acidity compared with unsubstituted phenol.

The propyl group is an electron-donating alkyl substituent that increases electron density on the aromatic ring through inductive effects. This activates the ring toward electrophilic aromatic substitution, particularly at the ortho and para positions relative to the hydroxyl group (positions 2, 4, and 6). The meta positioning of the propyl group affects the overall directing effects but does not strongly deactivate the ring.

From a physicochemical perspective, 3-propylphenol is moderately hydrophobic due to the presence of the alkyl chain, while the hydroxyl group provides limited polarity and hydrogen-bonding capability. As a result, it typically shows low to moderate water solubility but good solubility in organic solvents such as alcohols, ethers, and hydrocarbons.

Like other alkylphenols, 3-propylphenol can participate in hydrogen bonding both as a donor (via –OH) and as an acceptor (via the oxygen lone pairs). In the solid state, intermolecular hydrogen bonding between phenolic groups can lead to association or clustering.

Chemically, alkylphenols are important intermediates in organic synthesis and industrial chemistry. They can be used as precursors for antioxidants, surfactants, resins, and fine chemicals. The combination of a reactive phenolic group and a hydrophobic alkyl chain makes them useful in modifying surface-active and polymeric materials.

3-Propylphenol can be synthesized through alkylation of phenol using propylating agents under Friedel–Crafts conditions, although regioselectivity can be challenging and may yield mixtures of isomers (ortho-, meta-, and para-substituted products). Separation or selective synthesis methods are often required to obtain the desired isomer.

Historically, alkylphenols have been widely studied due to their role in industrial chemistry and their environmental relevance, as some derivatives are used in detergents, resins, and fuel additives.

Overall, 3-propylphenol is a meta-substituted alkylphenol consisting of a phenolic hydroxyl group and a propyl side chain on an aromatic ring. Its combination of mild polarity and hydrophobic character gives it useful chemical reactivity and typical properties of alkylphenolic compounds in organic and industrial chemistry.

References

2025. Machine Learning Predicts Non-Preferred and Preferred Vertebrate Hosts of Tsetse Flies (Glossina spp.) Based on Skin Volatile Emission Profiles. Journal of Chemical Ecology.
DOI: 10.1007/s10886-025-01582-6

2020. Substrate promiscuity of polyketide synthase enables production of tsetse fly attractants 3-ethylphenol and 3-propylphenol by engineering precursor supply in yeast. Scientific Reports.
DOI: 10.1038/s41598-020-66997-5

2017. Evaluation of Host-Derived Volatiles for Trapping Culicoides Biting Midges (Diptera: Ceratopogonidae). Journal of Chemical Ecology.
DOI: 10.1007/s10886-017-0860-x