Phenylmethylsulfonyl fluoride
[CAS 329-98-6]

Identification

• Classification: Chemical reagent >> Organic reagent >> Sulfonate / sulfinate
• Name: Phenylmethylsulfonyl fluoride
• Synonyms: alpha-Toluenesulfonyl fluoride; PMSF; Benzenemethanesulfonyl fluoride
• Molecular Formula: C₇H₇FO₂S
• Molecular Weight: 174.19
• CAS Registry Number: 329-98-6
• EC Number: 206-350-2
• SMILES: C1=CC=C(C=C1)CS(=O)(=O)F

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Melting point: 92 - 95 °C (Expl.)
• Boiling point: 285.7±19.0 °C 760 mmHg (Calc.)^*
• Flash point: 126.6±21.5 °C (Calc.)^*
• Solubility: Soluble ethanol: 100 mM, DMSO: 100 mM, water: <1 mg/mL (Expl.)
• Index of refraction: 1.522 (Calc.)^*

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

Safety Data

• Hazard Symbols: GHS05;GHS06 Danger
• Risk Statements: H301-H314
• Safety Statements: P260-P264-P270-P280-P301+P316-P301+P330+P331-P302+P361+P354-P304+P340-P305+P354+P338-P316-P321-P330-P363-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H301
Skin corrosion	Skin Corr.	1B	H314
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	2	H330
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Skin corrosion	Skin Corr.	1C	H314
Acute toxicity	Acute Tox.	3	H311
Skin corrosion	Skin Corr.	1A	H314

• Transport Information: UN 2928

Discovery and Applications

Phenylmethylsulfonyl fluoride (PMSF) is an organosulfur compound widely used as an irreversible inhibitor of serine proteases in biochemical research. It contains a sulfonyl fluoride functional group attached to a phenylmethyl (benzyl) substituent, giving the molecule both aromatic and highly electrophilic characteristics.

Structurally, PMSF consists of a benzyl group (C₆H₅–CH₂–) connected to a sulfonyl fluoride moiety (–SO₂F). The benzene ring provides a hydrophobic aromatic system with delocalized π-electrons, while the methylene bridge introduces flexibility between the aromatic ring and the reactive functional group. This arrangement allows the molecule to access enzyme active sites while maintaining structural stability.

The sulfonyl fluoride group is the key reactive center of PMSF. It consists of a sulfur atom double-bonded to two oxygen atoms and single-bonded to a fluorine atom and a carbon substituent. The sulfur atom is strongly electrophilic due to the electron-withdrawing effects of both oxygen and fluorine atoms. The S–F bond is particularly important because fluoride is a good leaving group under nucleophilic attack in biological environments.

PMSF acts primarily by reacting with the hydroxyl group of serine residues in the active sites of serine proteases. The nucleophilic oxygen of the serine side chain attacks the sulfur atom of the sulfonyl fluoride group, resulting in covalent modification of the enzyme and release of fluoride. This reaction forms a stable sulfonyl-enzyme adduct, effectively inactivating the protease in an irreversible manner.

The specificity of PMSF toward serine proteases arises from the presence of an accessible nucleophilic serine hydroxyl group in their catalytic triad. Once modified, the enzyme loses its ability to hydrolyze peptide bonds, thereby inhibiting proteolytic activity. This property makes PMSF useful in preventing unwanted protein degradation during protein extraction and purification procedures.

From a physicochemical perspective, PMSF exhibits both hydrophobic and polar characteristics. The phenyl ring contributes hydrophobicity, while the sulfonyl fluoride group is strongly polar and highly reactive. Despite containing polar functional groups, PMSF has limited water solubility and is typically handled in organic solvents such as isopropanol or ethanol before being added to aqueous systems.

Chemically, the sulfonyl fluoride group is the most reactive site in the molecule. It is stable under neutral conditions but highly susceptible to nucleophilic attack by hydroxyl, amine, or thiol groups under appropriate conditions. The benzyl group is relatively inert under typical biochemical conditions and mainly serves as a hydrophobic carrier that facilitates access to protein binding sites.

PMSF is known to be chemically unstable in aqueous solutions, particularly at higher pH values, where it can undergo hydrolysis to form inactive products. As a result, it is typically prepared fresh before use to ensure effective inhibition of target enzymes.

Overall, phenylmethylsulfonyl fluoride is a reactive sulfonyl fluoride compound consisting of a benzyl group attached to a highly electrophilic sulfur center. Its ability to covalently modify serine residues in proteases through irreversible inhibition underlies its widespread use as a biochemical tool for protecting proteins from enzymatic degradation.

References

2026. Correction: USP30-mediated Deubiquitination of Hexokinase 2 controls the metabolic fate of glucose and tumor progression. Cell Death & Disease.
DOI: 10.1038/s41419-026-08459-w

2026. CfAsh1 dominates H3K36 methylation and cooperates with CfSet2 to orchestrate chromatin-mediated pathogenicity in Colletotrichum fructicola. Phytopathology Research.
DOI: 10.1186/s42483-025-00408-3

2026. The Zn2Cys6 transcription factor FocTpc1 is a global regulator of growth, reproduction, pathogenicity, environmental adaptation, and autophagy in Fusarium oxysporum f. sp. cubense. Phytopathology Research.
DOI: 10.1186/s42483-026-00422-z