Antimony Pentachloride
Properties
| State | Liquid (fuming in air) |
| Color | Colorless to pale yellow (darkens on standing) |
| Solubility | Reacts violently with water; soluble in HCl, CS2, CHCl3 |
| Melting Point | 4 °C |
| Boiling Point | 140 °C (decomposes) |
About Antimony Pentachloride
Antimony pentachloride is a Lewis acid strong enough that it shows up in the chemistry of superacids — the world of compounds whose Hammett acidity functions are off the bottom of the conventional pH scale. The molecule itself is a discrete trigonal-bipyramidal SbCl5 unit (D3h symmetry) in solid, liquid, and gas phases, which sets it apart from transition-metal pentachlorides that tend to be ionic chloride-bridged dimers. Sb(V) here is a d¹⁰s⁰ ion with no remaining valence electrons and an empty axial coordination site that's hungry for a sixth ligand; nearly anything with a lone pair — a chloride from another SbCl5, a fluoride from HF, an ether oxygen, a phosphine — coordinates readily to give the octahedral [SbCl5L] adduct. That hunger is what makes SbCl5 useful as a chlorinating agent (it transfers chloride to alcohols and replaces –OH with –Cl), as a Friedel–Crafts catalyst (sometimes more active than AlCl3 for sluggish substrates), and as the precursor to SbF5 by halide exchange with HF. The SbF5/HF combination — fluoroantimonic acid — is the classical archetype of a superacid: SbF5 grabs a fluoride off HF to give [SbF6]⁻ and leaves behind a highly mobile H2F⁺ proton that's about 10¹⁶ times more acidic than 100% sulfuric acid by Hammett's H₀ scale, capable of protonating methane and ethane. The handling reality is that SbCl5 fumes in air, hydrolyzes violently in water, and corrodes most metals — the bottle that comes from the supplier is usually amber glass with a Teflon-lined cap.
Where you'll encounter it
If you've worked with superacids — protonating alkanes, doing carbocation chemistry on substrates that don't carry leaving groups, or studying isomerization of paraffins for petroleum-refining catalysis — you've encountered fluoroantimonic acid, and the SbF5 in that mixture started its life as SbCl5. Outside the superacid context, SbCl5 is a working reagent in some petroleum-isomerization processes (it converts straight-chain paraffins to branched isomers for higher-octane gasoline), in selective alkyl-chloride synthesis from primary alcohols, and as a one-electron oxidant for studying organic radical-cation chemistry. Most chemists who handle it do so once or twice in a career — it's a powerful but unpleasant reagent, and the practical workarounds (pre-formed chloride sources, milder Lewis acids, switched-on flow chemistry) are usually preferable when they exist.
Common Uses
- SbF5 precursor for fluoroantimonic-acid superacid chemistry
- Lewis-acid catalyst for difficult Friedel-Crafts alkylations and acylations
- Petroleum-isomerization catalyst for alkane branching
- Chlorinating reagent for alcohol-to-alkyl-chloride conversion
- One-electron oxidant for organic radical-cation studies
Safety Information
Reacts violently with water — small spills release HCl gas explosively, and the resulting solution is corrosive enough to eat through nitrile gloves. Fumes are immediately irritating to airways and eyes. Acute oral and inhalation toxicity are both Category 3; chronic exposure damages the respiratory tract and may produce long-term pulmonary fibrosis. OSHA PEL is 0.5 mg/m³ as antimony. Never handle outside a fume hood; never store near water sources or aqueous reagents. GHS H301, H314, H331, H372, H410.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.