Chlorine trifluoride (7790-91-2) Physical and Chemical Properties
Chlorine trifluoride
A highly reactive interhalogen fluorinating agent typically supplied as a liquefied compressed gas; requires specialized materials, handling procedures and supplier QA for industrial use.
| CAS Number | 7790-91-2 |
| Family | Interhalogen compound (halogen fluoride) |
| Typical Form | Liquefied compressed gas |
| Common Grades | EP |
Chlorine trifluoride is a covalent interhalogen compound of the halogen class, formally the fluoride of chlorine with empirical formula \(ClF_3\). Structurally it is derived from a trigonal bipyramidal electron-domain arrangement around the central chlorine atom with two equatorial lone pairs, giving a T-shaped molecular geometry and significant anisotropic electron density. The molecule is highly electron-withdrawing due to the three fluorine substituents; despite a formal zero net charge it displays extremely strong oxidizing and fluorinating behavior rather than classical Brønsted acidity/basicity.
As a low-boiling molecular gas that can be liquefied under moderate pressure, chlorine trifluoride is nonpolar in the sense of zero formal dipole surface area but is electronically activated for oxidation and fluorination reactions. It hydrolyzes violently with water to yield hydrogen fluoride and assorted chlorine oxides or elemental chlorine, and it reacts exothermically and often spontaneously with organic materials, many metals and metal oxides, and refractory materials. These properties underpin its use where aggressive fluorination or hypergolic oxidation is required, and they dictate stringent materials-of-construction, storage and handling controls in industrial settings.
Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
Reported density values vary with phase and temperature. Representative experimental values include: - Liquid: \(1.85\) (reported at \(51.8\,^\circ\mathrm{F}\)); noted to be denser than water and will sink. - Liquid (at boiling point): \(1.825\,\mathrm{g}\,\mathrm{mL}^{-1}\). - Gas (relative density): vapor density ~\(3.21\) (air = 1); gas density reported as \(3.14\,\mathrm{g}\,\mathrm{L}^{-1}\). - Solid: density \(2.530\,\mathrm{g}\,\mathrm{cm}^{-3}\) (at \(153\,\mathrm{K}\)).
These values reflect a compact packing in the condensed phases and a vapor considerably heavier than air; release of gas will tend to accumulate in low-lying areas.
Melting or Decomposition Point
- Melting/solidification temperature: \(-76.34\,^\circ\mathrm{C}\) (equivalently \(-105\,^\circ\mathrm{F}\)).
- Thermal decomposition: decomposes above \(220\,^\circ\mathrm{C}\) and can cause container failure or explosion on heating.
The substance exhibits a low melting point consistent with a small molecular interhalogen and decomposes at elevated temperatures to a mixture of halogen and halogen-oxide species.
Solubility in Water
Chlorine trifluoride reacts with water; it does not dissolve as an intact, stable neutral molecule. Hydrolysis proceeds vigorously producing hydrogen fluoride and chlorine-containing oxides or elemental chlorine with significant heat evolution. Practical consequence: direct contact with water (including ice) is violently reactive and generates corrosive and toxic aqueous products.
Solution pH (Qualitative Behavior)
Aqueous contact produces hydrogen fluoride (\(HF\)) and other acidic decomposition products; aqueous systems contaminated by chlorine trifluoride will become strongly acidic and highly corrosive. No directly measured equilibrium \(\mathrm{pH}\) of a stable ClF\(_3\) solution is available because the compound reacts rather than forming a stable dissolved molecular solution.
Chemical Properties
Acid–Base Behavior
Chlorine trifluoride is not a conventional Brønsted acid or base in isolation. Its interaction with protic media is dominated by hydrolysis and oxidation: reaction with water yields \(HF\) and chlorine oxides or \(Cl_2\), producing strongly acidic, corrosive mixtures. In practice pH effects in aqueous systems are a secondary consequence of hydrolysis products rather than intrinsic acid–base dissociation of the parent molecule.
Reactivity and Stability
- Strong oxidizer and aggressive fluorinating agent; capable of oxidizing or fluorinating a wide range of inorganic and organic substrates.
- Violent or explosive reactions reported with water, organic materials, fuels, many metals and metal oxides, halocarbons, nitrocompounds and certain polymers; spontaneous ignition on contact with many combustibles is documented.
- Decomposes in the vapor phase to species including \(Cl_2\), \(ClF\), \(ClO!F\), \(ClO_2F\), \(ClO_2\) and \(HF\), depending on moisture and reaction conditions.
- Considered unstable in moist air; contact with traces of moisture increases reactivity and corrosion (including attack on silica/quartz).
- Decomposition onset: above \(220\,^\circ\mathrm{C}\); heat of formation and phase-change energetics indicate significant stored chemical energy (heat of formation ~\(164.5\,\mathrm{kJ}\,\mathrm{mol}^{-1}\), heat of vaporization \(27.50\,\mathrm{kJ}\,\mathrm{mol}^{-1}\)).
Strict materials selection (compatible metals/alloys, avoidance of organics and siliceous materials) and exclusion of moisture are essential for stability.
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: \(ClF_3\).
- Molecular weight: \(92.45\,\mathrm{g}\,\mathrm{mol}^{-1}\).
- Exact/monoisotopic mass: \(91.9640622\).
- Topological polar surface area (TPSA): \(0\).
- Computed XLogP3: \(2.5\).
The electronic structure (three highly electronegative fluorine atoms bound to a central chlorine with two lone pairs) explains the combination of low molecular polarity metrics with extreme oxidative/fluorinating reactivity.
Constituent Ions
Chlorine trifluoride is a neutral covalent molecular species; there are no constituent ions in the intact compound under normal conditions.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS Registry Number: 7790-91-2
- EC number: 232-230-4
- UN Number / Shipping ID: 1749
- UN/NA ID and Guide: UN 1749
- UN Hazard Class (subsidiary risks): 2.3 (toxic gas); Subsidiary: 5.1 (oxidizer), 8 (corrosive)
- UNII: 921841L3N0
- InChIKey: JOHWNGGYGAVMGU-UHFFFAOYSA-N
- ChEBI ID: CHEBI:30123
- DSSTox Substance ID: DTXSID90893948
Synonyms and Common Names
Common synonyms and designations found in industrial and technical contexts include: - chlorine trifluoride - ClF3 - trifluorochlorine - trifluoro-lambda3-chlorane - chlorotrifluoride - trifluoridochlorine
(Several legacy and depositor-supplied variations exist; the primary systematic formula designation is \(ClF_3\).)
Industrial and Commercial Applications
Functional Roles and Use Sectors
Chlorine trifluoride is used primarily as a potent fluorinating and oxidizing agent where aggressive, non-aqueous fluorination is required. Key industrial roles include: - Fluorinating agent for conversion steps in specialty inorganic and organofluorine chemistry. - Processing reagent in nuclear fuel cycles for conversion of uranium to gaseous uranium hexafluoride. - Hypergolic oxidizer / igniter in certain rocket-propulsion research and historical propellant applications. - Etchant for silicon and related materials in semiconductor and photovoltaic manufacturing (low-temperature silicon etching). - Pyrolysis inhibitor and treatment agent in some fluoropolymer processes.
Typical Application Examples
Representative applications in practice: - Conversion of metal fluorides or oxyfluorides during nuclear fuel reprocessing to volatile fluorides. - Controlled fluorination of robust inorganic substrates where milder fluorinating reagents are ineffective. - Use as an oxidizing component or initiator in propellant or incendiary formulations under tightly controlled conditions (historical and niche uses). - Low-temperature dry etching of single-crystal silicon in specialized semiconductor process steps.
No concise product application summary can substitute for process-specific safety and compatibility evaluation; selection is driven by the unique combination of extreme fluorinating power and limited handling compatibility.
Safety and Handling Overview
Health and Environmental Hazards
- Acute inhalation hazard: vapors are highly irritating and potentially fatal. Reported acute inhalation toxicity values include LC50 (rat) ~\(299\,\mathrm{ppm}/1\,\mathrm{h}\) and mouse LC50 \(178\,\mathrm{ppm}/1\,\mathrm{h}\).
- Occupational exposure limits: ceiling recommendations and limits commonly cited are \(0.1\,\mathrm{ppm}\) (ceiling value) for occupational exposure (per various exposure guidelines); IDLH values are reported in the range of \(12\)–\(20\,\mathrm{ppm}\).
- AEGL (example short-duration values): 10 min — \(0.12\,\mathrm{ppm}\) (AEGL-1), \(8.1\,\mathrm{ppm}\) (AEGL-2), \(84\,\mathrm{ppm}\) (AEGL-3); values for longer durations show reduced AEGL-2/3 thresholds.
- Corrosivity: liquid and concentrated vapor cause severe skin and eye burns and can produce deep tissue injury; inhalation can cause pulmonary edema and severe respiratory injury; systemic fluoride toxicity can occur from formation of soluble fluoride species.
- Environmental toxicity: very toxic to aquatic life; release to water generates corrosive, toxic species including \(HF\) and chlorine oxides.
- Fire/explosion behavior: the substance does not burn but is a strong oxidizer that can support and in many cases initiate combustion of organic matter and many otherwise noncombustible materials; contact with water or organics may be violently exothermic or explosive. Containers exposed to fire may rupture or “rocket.”
First-aid measures are emergency and symptom-driven: immediate removal from exposure, copious irrigation for skin/eye contact, respiratory support, and rapid medical evaluation for potential pulmonary injury. Medical management of fluoride-related systemic effects includes symptomatic/supportive care and calcium administration where indicated.
Storage and Handling Considerations
- Store cylinders and containers in a cool, dry, well-ventilated area, separated from water, organics, reducers, acids, alkalies, and incompatible metals or refractory materials. Outside or detached storage locations are preferred.
- Materials of construction: compatibility assessment is critical; silica, many polymers, and certain metals and metal oxides are incompatible. Procedures and equipment must be free of organic residues and moisture; lines and vessels must be purged and dried with inert gas prior to contact.
- Handling controls: use engineered local exhaust ventilation and leak-detection systems; restrict access and provide emergency isolation measures. Maintain cylinder restraints and pressure-relief protections appropriate for liquefied compressed gases.
- Personal protective equipment: positive-pressure self-contained breathing apparatus (SCBA) for emergency interventions; full chemical-protective suits and face protection for potential contact; readily available eyewash and deluge-shower facilities for liquid exposure.
- Spill and fire response: isolate area and evacuate as required; prevent accumulation in low areas; avoid directing water at liquid source (water contact can be violently reactive) but water spray or fog may be used cautiously to disperse vapors or cool adjacent containers where recommended by emergency procedures. Do not use ordinary dry chemical extinguishers on the material itself; firefighting involving tanks should be conducted from maximum safe distance or by specialists using unmanned systems.
- Waste and decontamination: do not attempt neutralization or contact with incompatible materials; specialists should perform neutralization and disposal consistent with hazardous-waste regulations; avoid introducing water into contaminated equipment except as part of validated neutralization systems.
For detailed, situation-specific hazard, transport and regulatory guidance, consult the product-specific Safety Data Sheet and applicable local legislation.
