Perfluorohexanesulfonic Acid (355-46-4) Physical and Chemical Properties
Perfluorohexanesulfonic Acid
A perfluorinated sulfonic acid commonly used as an analytical standard and intermediate in PFAS-related R&D, materials development and formulation testing.
| CAS Number | 355-46-4 |
| Family | Perfluoroalkyl sulfonic acids (PFAS) |
| Typical Form | Powder or crystalline solid |
| Common Grades | EP, Technical Grade, USP |
Perfluorohexanesulfonic acid is a perfluoroalkanesulfonic acid (a perfluorosulfonic acid) in which the six-carbon backbone bears fully fluorinated carbon substituents and a terminal sulfonic acid functionality. Structurally it is represented by the molecular formula \(\ce{C6HF13O3S}\), and its systematic name is 1,1,2,2,3,3,4,4,5,5,6,6,6‑tridecafluorohexane‑1‑sulfonic acid. The perfluoroalkyl chain imparts extremely low polarizability of the hydrocarbon backbone but a strong electron-withdrawing character from the twelve to thirteen fluorine atoms; the sulfonic acid headgroup provides a strongly acidic, highly polar site that dominates acid–base and ionization behavior in condensed phases.
The compound ionizes readily (estimated \(\mathrm{p}K_a \approx 0.14\)) to give the corresponding perfluorohexanesulfonate anion under typical environmental and physiological pH conditions; therefore, in neutral and basic media it exists predominantly as the anion and behaves as a persistent, highly mobile surfactant-like species. The combination of a hydrophobic, fluorinated tail and a charged, highly hydrated sulfonate head gives amphiphilic phase behavior (surface activity, micelle formation in concentrated systems) and a propensity to partition to interfaces and organic coatings while exhibiting low volatility and resistance to hydrolysis and photolysis. Persistent bioaccumulative tendencies and long biological elimination half-lives in humans and wildlife are characteristic for this C6 perfluoroalkyl sulfonic acid class.
Common commercial grades reported for this substance include: EP, Technical Grade, USP.
Basic Physical Properties
Density
Measured density: \(1.841\ \mathrm{g}\,\mathrm{cm}^{-3}\).
Commentary: The high density relative to typical organic liquids reflects the heavy fluorine content and compact perfluoroalkyl structure. Dense, fluorinated liquids and solids often display low compressibility and high chemical inertness.
Melting Point
No experimentally established value for this property is available in the current data context.
Boiling Point
Reported boiling point: \(238\text{–}239\,^\circ\mathrm{C}\).
Commentary: The relatively high boiling range is consistent with a small, heavy, and strongly interacting molecule that is capable of hydrogen-bonding via the sulfonic acid group in the undissociated state and exhibits low vapor pressure at ambient temperatures.
Vapor Pressure
Estimated vapor pressure at \(25\,^\circ\mathrm{C}\): \(0.0046\ \mathrm{mmHg}\).
Commentary: The low vapor pressure indicates limited volatility under ambient conditions; atmospheric partitioning is nevertheless observed in both gas and particle phases because of association with aerosols and the compound’s surfactant-like behavior.
Flash Point
No experimentally established value for this property is available in the current data context.
Chemical Properties
Solubility and Phase Behavior
Perfluorohexanesulfonic acid behaves as a strongly acidic surfactant: it is essentially fully ionized at environmental and physiological pH (estimated \(\mathrm{p}K_a \approx 0.14\)), so aqueous solutions are dominated by the perfluorohexanesulfonate anion. The amphiphilic nature leads to surface activity and micelle-like aggregation at elevated concentrations; some fraction associated with interfaces or organic matrices can be effectively non‑volatile despite the low parent vapor pressure. In waters and soils the anionic form shows high mobility (reported field-based \(K_{\mathrm{oc}}\approx 9.3\)), low sorption to organic carbon, and modest potential for bioconcentration (reported BCF ≈ 10; field-based BAF ≈ 70).
Solubility remarks: explicit aqueous solubility values are not provided in the available data; the substance’s ionized form is water‑dispersible, whereas the neutral acid (in strongly acidic media) is less hydrophilic.
Reactivity and Stability
Chemical stability: reported as stable under recommended storage conditions. The sulfonic acid headgroup is thermally robust and the perfluoroalkyl chain is highly resistant to hydrolytic, oxidative and photolytic cleavage under typical ambient conditions. Hydrolysis is not expected to be a significant degradation pathway; abiotic atmospheric oxidation by OH radicals is slow (estimated atmospheric half‑life ≈ 115 days). Incompatible materials include strong oxidizing agents. Thermal decomposition or combustion can generate toxic gases (e.g., hydrogen fluoride and sulfur oxides); appropriate fire‑fighting precautions should be used.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context.
Commentary: Standard thermodynamic quantities (standard enthalpy of formation, heat capacity at constant pressure) are not present in the available experimental set; reliable values would require calorimetric determinations or validated computational thermochemistry for a highly fluorinated sulfonic acid.
Molecular Parameters
Molecular Weight and Formula
Molecular formula: \(\ce{C6HF13O3S}\).
Molecular weight (reported): \(400.12\).
Exact/monoisotopic mass: \(399.9438812\).
Commentary: The molecular weight and exact mass reflect the multiple fluorine substitutions; precise masses are useful for mass-spectrometric monitoring of the deprotonated anion and oligomeric species.
LogP and Polarity
Reported computed XLogP3 (lipophilicity descriptor): \(3.7\).
Topological polar surface area (TPSA): \(62.8\ \text{Å}^2\).
Hydrogen-bond donor count: 1 (the sulfonic acid proton in the undissociated state).
Hydrogen-bond acceptor count: 16.
Rotatable bond count: 5.
Commentary: A computed XLogP of 3.7 indicates intrinsic hydrophobicity of the perfluoroalkyl backbone; however, the strongly acidic sulfonic group drives aqueous solubility and anionic behavior at neutral pH, reducing classical lipophilic partitioning in biological systems and favoring protein binding (e.g., serum albumin) rather than partitioning to lipid phases.
Structural Features
The molecule combines a fully fluorinated hexyl (perfluorohexyl) tail and a terminal sulfonic acid group. The perfluoroalkyl segment is electronically and sterically distinct from hydrocarbon chains: it confers chemical inertness, high density, and strong C–F bond strength. The sulfonic acid headgroup is a strong acid and under most conditions is present in anionic form (\(\ce{RSO3^-}\)), which coordinates strongly with water and protein binding sites. The molecular geometry minimizes polarizability of the tail while concentrating polarity at the sulfonate, producing surfactant‑like and interfacial partitioning properties.
SMILES: C(C(C(C(F)(F)S(=O)(=O)O)(F)F)(F)F)(C(C(F)(F)F)(F)F)(F)F
InChI: InChI=1S/C6HF13O3S/c7-1(8,3(11,12)5(15,16)17)2(9,10)4(13,14)6(18,19)23(20,21)22/h(H,20,21,22)
InChIKey: QZHDEAJFRJCDMF-UHFFFAOYSA-N
(These identifiers are provided as machine identifiers for structure and spectral confirmation; use in analytical workflows for mass spectrometry and chromatographic method development.)
Identifiers and Synonyms
Registry Numbers and Codes
CAS number: 355-46-4
Other reported identifiers (selection): UNII ZU6Y1E592S; EC number 206-587-1; several curated registry IDs are associated with the substance.
Synonyms and Structural Names
Common synonyms and alternate names reported include: perfluorohexanesulfonic acid; PFHxS; perfluorohexane-1-sulfonic acid; perfluorohexane sulfonic acid; perfluorohexane-1-sulphonic acid; 1,1,2,2,3,3,4,4,5,5,6,6,6‑tridecafluorohexane-1‑sulfonic acid; tridecafluorohexane-1-sulfonic acid. Technical and assay descriptors such as “Perfluorohexanesulfonic Acid (Technical Grade)” and concentration formats (e.g., standard solutions in methanol or acetonitrile) are used in analytical contexts.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Perfluorohexanesulfonic acid has been used historically and as a precursor in the manufacture of perfluoroalkyl sulfonate products. Representative uses reported include formulations in aqueous film‑forming foams (AFFF) for firefighting, stain and water‑repellent treatments for textiles and carpets, coatings for leather and apparel membranes, and as a chemical intermediate for specialty fluorinated products. Environmental monitoring data indicate historical release pathways from these uses into wastewater, soils, and ambient air.
Role in Synthesis or Formulations
In fluorochemical manufacturing, perfluoroalkanesulfonyl fluorides are produced by electrochemical fluorination or other fluorination strategies and can be hydrolyzed to produce sulfonic acids or converted to salts for use in formulations. The sulfonic acid (and its salts) function as ionic surfactants and surface‑active agents in product formulations; salts (e.g., potassium or ammonium perfluorohexanesulfonate) are commonly handled for downstream applications.
If a concise, product‑specific application summary is required for procurement or formulation decisions, no single universal application statement is available here; selection in practice is governed by compatibility with product matrices and regulatory considerations described below.
Safety and Handling Overview
Acute and Occupational Toxicity
Hazard classification and acute effects: hazard statements reported include acute toxicity by ingestion, dermal contact and inhalation; skin corrosion/irritation and serious eye damage/irritation; and target organ toxicity from repeated exposure. Reported GHS hazard statements include H302, H312, H314, H332 (acute routes) and H373 for possible organ damage on repeated exposure.
Toxicokinetics and chronic exposure: human biomonitoring and epidemiology indicate ubiquitous exposure in many populations with long biological elimination half‑lives (human geometric mean serum elimination half‑life has been estimated to be on the order of thousands of days in some analyses). Associations have been reported between elevated serum concentrations and altered lipid parameters, thyroid hormone perturbation in susceptible subjects, developmental outcomes, and neurodevelopmental or reproductive endpoints in selected cohorts. Animal studies identify liver effects, effects on lipoprotein metabolism, developmental neurotoxicity markers, and alterations in thyroid hormone–dependent pathways. Reported chronic oral reference dose estimates (as reported in toxicity summaries) include extremely low values in the range of \(4\times10^{-10}\ \mathrm{mg}\,\mathrm{kg}^{-1}\,\mathrm{day}^{-1}\) (one reported central estimate) and referenced chronic guidance values in the order of \(2\times10^{-5}\ \mathrm{mg}\,\mathrm{kg}^{-1}\,\mathrm{day}^{-1}\) in other assessments; users should treat these as indicative of the low exposure thresholds used in risk assessment and consult product‑specific safety documentation for operational limits.
Emergency treatment: standard decontamination and medical supportive measures apply for ingestion, inhalation or dermal/ocular exposure: remove contaminated clothing, flush affected areas with water, maintain airway and breathing, and seek prompt medical attention.
Storage and Handling Considerations
Handling: avoid inhalation of dust or aerosols and avoid skin and eye contact. Use engineering controls (local exhaust, fume hoods) where dust or aerosols may be generated. Inspect and select chemical‑resistant gloves and impervious clothing appropriate to anticipated exposure levels.
Personal protective equipment (PPE): eye protection (safety glasses with side shields or goggles), chemically resistant gloves, respiratory protection for particulate exposures (e.g., P95/P1) or for mixed gas/particulate risks use appropriate combined cartridges; selection should follow institutional respiratory protection programs and testing standards.
Storage: keep containers tightly closed in a dry, well‑ventilated area; avoid storage with strong oxidizing agents. Label containers and manage inventories to minimize uncontrolled releases.
Accidental release and disposal: avoid generation of dust; contain spills, collect in suitable containers and dispose of via licensed hazardous waste services with attention to environmental persistence and potential mobility in water and soils. For waste management, consider the compound’s potential for environmental persistence and transport; follow local regulatory requirements.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
